/* This file is part of the KDE project
   Copyright (C) 2003-2017 Jarosław Staniek <staniek@kde.org>

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public
   License as published by the Free Software Foundation; either
   version 2 of the License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public License
   along with this program; see the file COPYING.  If not, write to
   the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
*/

#ifndef KDB_CONNECTION_H
#define KDB_CONNECTION_H

#include "KDbCursor.h"
#include "KDbDriver.h"
#include "KDbPreparedStatement.h"
#include "KDbTableSchema.h"
#include "KDbTransaction.h"
#include "KDbTristate.h"

class KDbConnectionData;
class KDbConnectionOptions;
class KDbConnectionPrivate;
class KDbConnectionProxy;
class KDbDriver;
class KDbProperties;
class KDbRecordData;
class KDbRecordEditBuffer;
class KDbServerVersionInfo;
class KDbSqlResult;
class KDbTableSchemaChangeListener;
class KDbTableSchemaChangeListenerPrivate;
class KDbTransactionGuard;
class KDbVersionInfo;

/*! @short Provides database connection, allowing queries and data modification.

 This class represents a database connection established within a data source.
 It supports data queries and modification by creating client-side database cursors.
 Database transactions are supported.
*/
class KDB_EXPORT KDbConnection : public KDbResultable
{
    Q_DECLARE_TR_FUNCTIONS(KDbConnection)
public:

    /*! Opened connection is automatically disconnected and removed
     from driver's connections list.
     Note for driver developers: you should call destroy()
     from you KDbConnection's subclass destructor. */
    ~KDbConnection() override;

    /*! @return parameters that were used to create this connection. */
    KDbConnectionData data() const;

    /*! @return the driver used for this connection. */
    KDbDriver* driver() const;

    /*!
    @brief Connects to driver with given parameters.
    @return true if successful.

     Note: many database drivers may require connData.databaseName() to be specified
     because explicit database name is needed to perform connection (e.g. SQLite, PostgreSQL).
     MySQL does not require database name; KDbConnection::useDatabase() can be called later.
    */
    bool connect();

    /*! @return true, if connection is properly established. */
    bool isConnected() const;

    /*! @return true, both if connection is properly established
     and any database within this connection is properly used
     with useDatabase(). */
    bool isDatabaseUsed() const;

    /*! @return generic options for a single connection.
        The options are accessible using key/value pairs. This enables extensibility
        depending on driver's type and version. */
    KDbConnectionOptions *options();

    /*! Reimplemented, also clears sql string.
     @sa recentSqlString() */
    void clearResult();

    /*! @brief Disconnects from driver with given parameters.

     The database (if used) is closed, and any active transactions
     (if supported) are rolled back, so commit these before disconnecting,
     if you'd like to save your changes. */
    bool disconnect();

    /*! @return list of database names for opened connection.
     If @a also_system_db is true, the system database names are also returned. */
    QStringList databaseNames(bool also_system_db = false);

    /*! @return true if database @a dbName exists.
     If @a ignoreErrors is true, error flag of connection
      won't be modified for any errors (it will quietly return),
      else (ignoreErrors == false) we can check why the database does
      not exist using error(), errorNum() and/or errorMsg(). */
    bool databaseExists(const QString &dbName, bool ignoreErrors = true);

    /*! @brief Creates new database with name @a dbName, using this connection.

     If database with @a dbName already exists, or other error occurred,
     false is returned.
     For file-based drivers, @a dbName should be equal to the database
     filename (the same as specified for KDbConnectionData).

     See docs/kdb_issues.txt document, chapter "Table schema, query schema, etc. storage"
     for database schema documentation (detailed description of kexi__* 'system' tables).

     @see useDatabase() */
    bool createDatabase(const QString &dbName);

    /*!
    @brief Opens an existing database specified by @a dbName.

     If @a kexiCompatible is true (the default) initial checks will be performed
     to recognize database Kexi-specific format. Set @a kexiCompatible to false
     if you're using native database (one that have no Kexi System tables).
     For file-based drivers, @a dbName can be skipped, so the same as specified for
     KDbConnectionData is used.
     @return true on success, false on failure.
     If user has cancelled this action and @a cancelled is not 0, *cancelled is set to true. */
    bool useDatabase(const QString &dbName = QString(), bool kexiCompatible = true, bool *cancelled = nullptr,
                     KDbMessageHandler* msgHandler = nullptr);

    /*!
    @brief Closes currently used database for this connection.

     Any active transactions (if supported) are rolled back,
     so commit these before closing, if you'd like to save your changes. */
    bool closeDatabase();

    /*! @brief Get the name of the current database

    @return name of currently used database for this connection or empty string
      if there is no used database */
    QString currentDatabase() const;

    /*! @brief Drops database with name @a dbName.

     if dbName is not specified, currently used database name is used
     (it is closed before dropping).
    */
    bool dropDatabase(const QString &dbName = QString());

    /*! @return names of all the @a objectType (see @a ObjectType in KDbGlobal.h)
    schemas stored in currently used database. KDb::AnyObjectType can be passed
    as @a objectType to get names of objects of any type.
    The list ordered is based on object identifiers.
    Only names that are identifiers (checked using KDb::isIdentifier()) are returned.
    If @a ok is not 0 then variable pointed by it will be set to the result.
    On error, the function returns empty list.
    @see kdbSystemTableNames() tableNames(int,bool*) */
    QStringList objectNames(int objectType = KDb::AnyObjectType, bool* ok = nullptr);

    /*! @return names of all table schemas stored in currently
     used database. If @a alsoSystemTables is true,
     internal KDb system table names (kexi__*) are also returned.
     The list ordered is based on object identifiers.
     Only names that are identifiers (checked using KDb::isIdentifier()) are returned.
     If @a ok is not 0 then variable pointed by it will be set to the result.
     On error, the function returns empty list.
     @see kdbSystemTableNames() objectNames(int,bool*) */
    QStringList tableNames(bool alsoSystemTables = false, bool* ok = nullptr);

    /*! @return true if table with name @a tableName exists in the database.
     @return @c false if it does not exist or @c cancelled if error occurred.
     The lookup is case insensitive.
     This method can be much faster than tableNames(). */
    tristate containsTable(const QString &tableName);

    /*! @return list of internal KDb system table names
     (kexi__*). This does not mean that these tables can be found
     in currently opened database. Just static list of table
     names is returned.

     The list contents may depend on KDb library version;
     opened database can contain fewer 'system' tables than in current
     KDb implementation, if the current one is newer than the one used
     to build the database.
     @todo this will depend on KDb lib version */
    static QStringList kdbSystemTableNames();

    /*! @return server version information for this connection.
     If database is not connected (i.e. isConnected() is false) null KDbServerVersionInfo is returned. */
    KDbServerVersionInfo serverVersion() const;

    /*! @return version information for this connection.
     If database is not used (i.e. isDatabaseUsed() is false) null KDbVersionInfo is returned.
     It can be compared to drivers' and KDb library version to maintain
     backward/upward compatiblility. */
    KDbVersionInfo databaseVersion() const;

    /*! @return KDbProperties object allowing to read and write global database properties
     for this connection. */
    KDbProperties databaseProperties() const;

    /*! @return ids of all table schema names stored in currently
     used database. These ids can be later used as argument for tableSchema().
     This is a shortcut for objectIds(KDb::TableObjectType).
     Internal KDb system tables (kexi__*) are not available here
     because these have no identifiers assigned (more formally: id=-1).
     If @a ok is not 0 then variable pointed by it will be set to the result.

     @note The fact that given id is on the returned list does not mean
     that tableSchema( id ) returns anything. The table definition can be broken,
     so you have to double check this.

     Only IDs of objects with names that are identifiers (checked using KDb::isIdentifier())
     are returned.
     @see queryIds()
     */
    QList<int> tableIds(bool* ok = nullptr);

    /*! @return ids of all database query schemas stored in currently
     used database. These ids can be later used as argument for querySchema().
     This is a shortcut for objectIds(KDb::QueryObjectType).
     If @a ok is not 0 then variable pointed by it will be set to the result.

     @note The fact that given id is on the returned list does not mean
     that querySchema( id ) returns anything. The query definition can be broken,
     so you have to double check this.

     Only IDs of objects with names that are identifiers (checked using KDb::isIdentifier())
     are returned.
     @see tableIds()
     */
    QList<int> queryIds(bool* ok = nullptr);

    /*! @return names of all schemas of object with @a objectType type
     that are stored in currently used database.
     If @a ok is not 0 then variable pointed by it will be set to the result.

     @note The fact that given id is on the returned list does not mean
     that the definition of the object is valid,
     so you have to double check this.

     Only IDs of objects with names that are identifiers (checked using KDb::isIdentifier())
     are returned.
     @see tableIds() queryIds() */
    QList<int> objectIds(int objectType, bool* ok = nullptr);

    /**
     * @brief Starts a new database transaction
     *
     * @return KDbTransaction object. If transaction has been started successfully returned object
     * points to it, otherwise null transaction is returned.
     *
     * For drivers that allow single transaction per connection
     * (KDbDriver::features() && SingleTransactions) this method can be called once and that
     * transaction will be default one (setDefaultTransaction() will be called).
     * For drivers that allow multiple transactions per connection no default transaction is
     * set automatically in beginTransaction(). setDefaultTransaction() can be called by hand.
     *
     * @see setDefaultTransaction(), defaultTransaction().
     */
    KDbTransaction beginTransaction();

    /**
     * @brief Commits specified transaction for this connection
     *
     * If @a transaction is not active and default transaction (obtained from defaultTransaction())
     * exists, the default one will be committed. If neither the default one is not present returns
     * @c true if IgnoreInactive is set in @a options or @c false if IgnoreInactive is not set in
     * @a options.
     *
     * @return @c false on any error.
     *
     * On successful commit, @a transaction object will point to a null transaction.
     * After commiting a default transaction, there is no default transaction anymore.
     */
    bool commitTransaction(KDbTransaction transaction = KDbTransaction(),
                           KDbTransaction::CommitOptions options = KDbTransaction::CommitOptions());

    /**
     * @brief Rolls back specified transaction for this connection
     *
     * If @a transaction is not active and default transaction (obtained from defaultTransaction())
     * exists, the default one will be rolled back. If neither default one is present @c true is
     * returned if IgnoreInactive is set for @a options or @c false if IgnoreInactive is not set in
     * @a options.
     *
     * @return @c false on any error.
     *
     * On successful rollback, @a transaction object will point to a null transaction.
     * After rollong back a default transaction, there is no default transaction anymore.
     */
    bool rollbackTransaction(KDbTransaction trans = KDbTransaction(),
                             KDbTransaction::CommitOptions options = KDbTransaction::CommitOptions());

    /**
     * @brief Returns handle of default transaction for this connection
     *
     * Null transaction is returned if there is no such a transaction declared.
     * If transactions are supported any operation on database (e.g. inserts) that are started
     * without specifying a transaction context, are be performed in the context of this transaction.
     * Returned null transaction doesn't mean that there are no transactions started at all.
     * Default transaction can be defined automatically for certain drivers, see beginTransaction().
     *
     * @see KDbDriver::transactionsSupported()
     */
    KDbTransaction defaultTransaction() const;

    /**
     * @brief Sets default transaction
     *
     * Default transaction is used as a context for data modifications for this connection when no
     * specific transaction is provided.
     */
    void setDefaultTransaction(const KDbTransaction& trans);

    /**
     * @brief Returns set of handles of currently active transactions
     *
     * @note In multithreading environment some of these transactions can be already inactive after
     * calling this method. Use KDbTransaction::isActive() to check that. Inactive transaction
     * handle is useless and can be safely ignored.
     */
    QList<KDbTransaction> transactions();

    /*! @return true if "auto commit" option is on.

     When auto commit is on (the default on for any new KDbConnection object), every SQL statement
     that manipulates data in the database implicitly starts a new transaction. This transaction is
     automatically committed after successful statement execution or rolled back on error.

     For drivers that do not support transactions (see KDbDriver::features())
     this method shouldn't be called because it does nothing ans always returns false.

     No internal KDb object should changes this option, although auto commit's
     behavior depends on database engine's specifics. Engines that support only single
     transaction per connection (see KDbDriver::SingleTransactions),
     use this single connection for autocommiting, so if there is already transaction
     started by the KDb user program (with beginTransaction()), this transaction
     is committed before any statement that manipulates data. In this situation
     default transaction is also affected (see defaultTransaction()).

     Only for drivers that support nested transactions (KDbDriver::NestedTransactions),
     autocommiting works independently from previously started transaction,

     For other drivers set this option off if you need use transaction
     for grouping more statements together.

     NOTE: nested transactions are not yet implemented in KDb API.
    */
    bool autoCommit() const;

    /*! Changes auto commit option. This does not affect currently started transactions.
     This option can be changed even when connection is not established.
     @see autoCommit() */
    bool setAutoCommit(bool on);

    /*! Connection-specific string escaping. Default implementation uses driver's escaping.
     Use KDbEscapedString::isValid() to check if escaping has been performed successfully.
     Invalid strings are set to null in addition, that is KDbEscapedString::isNull() is true,
     not just isEmpty().
    */
    virtual KDbEscapedString escapeString(const QString& str) const;

    /*! Prepares SELECT query described by a raw statement @a sql.
     @return opened cursor created for results of this query
     or @c nullptr if there was any error. Ownership of the returned object is passed
     to the caller.
     KDbCursor can have optionally applied @a options (one of more selected from KDbCursor::Options).
     Preparation means that returned cursor is created but not opened.
     Open this when you would like to do it with KDbCursor::open().

     Note for driver developers: you should initialize cursor engine-specific
     resources and return KDbCursor subclass' object
     (passing @a sql and @a options to its constructor).
    */
    virtual KDbCursor* prepareQuery(const KDbEscapedString& sql,
                                    KDbCursor::Options options = KDbCursor::Option::None) /*Q_REQUIRED_RESULT*/ = 0;

    /*! @overload
     Prepares query described by @a query schema. @a params are values of parameters that
     will be inserted into places marked with [] before execution of the query.

     Note for driver developers: you should initialize cursor engine-specific
     resources and return KDbCursor subclass' object
     (passing @a query and @a options to it's constructor).
     Kexi SQL and driver-specific escaping is performed on table names.
    */
    KDbCursor* prepareQuery(KDbQuerySchema* query, const QList<QVariant>& params,
                            KDbCursor::Options options = KDbCursor::Option::None) Q_REQUIRED_RESULT;

    /*! @overload
     Prepares query described by @a query schema without parameters.
    */
    virtual KDbCursor* prepareQuery(KDbQuerySchema* query,
                                    KDbCursor::Options options = KDbCursor::Option::None) /*Q_REQUIRED_RESULT*/ = 0;

    /*! @overload
     Statement is build from data provided by @a table schema, it is like "select * from table_name".*/
    KDbCursor* prepareQuery(KDbTableSchema* table,
                            KDbCursor::Options options = KDbCursor::Option::None) Q_REQUIRED_RESULT;

    /*! Executes SELECT query described by a raw SQL statement @a sql.
     @return opened cursor created for results of this query
     or 0 if there was any error on the cursor creation or opening.
     Ownership of the returned object is passed to the caller.
     KDbCursor can have optionally applied @a options.
     Identifiers in @a sql that are the same as keywords
     in KDbSQL dialect or the backend's SQL have to be escaped.
     */
    KDbCursor* executeQuery(const KDbEscapedString& sql,
                            KDbCursor::Options options = KDbCursor::Option::None) Q_REQUIRED_RESULT;

    /*! @overload executeQuery(const KDbEscapedString&, int)
     @a params are values of parameters that
     will be inserted into places marked with [] before execution of the query.

     Statement is build from data provided by @a query schema.
     Kexi SQL and driver-specific escaping is performed on table names. */
    KDbCursor* executeQuery(KDbQuerySchema* query, const QList<QVariant>& params,
                            KDbCursor::Options options = KDbCursor::Option::None) Q_REQUIRED_RESULT;

    /*! @overload */
    KDbCursor* executeQuery(KDbQuerySchema* query,
                            KDbCursor::Options options = KDbCursor::Option::None) Q_REQUIRED_RESULT;

    /*! @overload
     Executes query described by @a query schema without parameters.
     Statement is build from data provided by @a table schema,
     it is like "select * from table_name".*/
    KDbCursor* executeQuery(KDbTableSchema* table,
                            KDbCursor::Options options = KDbCursor::Option::None) Q_REQUIRED_RESULT;

    /*! Deletes cursor @a cursor previously created by functions like executeQuery()
     for this connection.
     There is an attempt to close the cursor with KDbCursor::close() if it was opened.
     Anyway, at last cursor is deleted.
     @return true if cursor is properly closed before deletion. */
    bool deleteCursor(KDbCursor *cursor);

    /*! @return schema of a table pointed by @a tableId, retrieved from currently
     used database. The schema is cached inside connection,
     so retrieval is performed only once, on demand. */
    KDbTableSchema* tableSchema(int tableId);

    /*! @return schema of a table pointed by @a tableName, retrieved from currently
     used database. KDb system table schema can be also retrieved.
     @see tableSchema( int tableId ) */
    KDbTableSchema* tableSchema(const QString& tableName);

    /*! @return schema of a query pointed by @a queryId, retrieved from currently
     used database. The schema is cached inside connection,
     so retrieval is performed only once, on demand. */
    KDbQuerySchema* querySchema(int queryId);

    /*! @return schema of a query pointed by @a queryName, retrieved from currently
     used database.  @see querySchema( int queryId ) */
    KDbQuerySchema* querySchema(const QString& queryName);

    /*! Sets @a queryName query obsolete by moving it out of the query sets, so it will not be
     accessible by querySchema( const QString& queryName ). The existing query object is not
     destroyed, to avoid problems when it's referenced. In this case,
     a new query schema will be retrieved directly from the backend.

     For now it's used in KexiQueryDesignerGuiEditor::storeLayout().
     This solves the problem when user has changed a query schema but already form still uses
     previously instantiated query schema.
     @return true if there is such query. Otherwise the method does nothing. */
    bool setQuerySchemaObsolete(const QString& queryName);

    //! Options for querying records
    //! @since 3.1
    enum class QueryRecordOption {
        AddLimitTo1 = 1, //!< Adds a "LIMIT 1" clause to the query for optimization purposes
                         //!< (it should not include one already)
        Default = AddLimitTo1
    };
    Q_DECLARE_FLAGS(QueryRecordOptions, QueryRecordOption)

    /*! Executes query for a raw statement @a sql and stores first record's data inside @a data.
     This is a convenient method when we need only first record from query result,
     or when we know that query result has only one record.
     If @a options includes AddLimitTo1 value, "LIMIT 1" clause is added to the query (this is the default).
     Caller should make sure it is not there in the @a sql already.
     @return @c true if query was successfully executed and first record has been found,
     @c false on data retrieving failure, and @c cancelled if there's no single record available. */
    tristate querySingleRecord(const KDbEscapedString& sql, KDbRecordData* data,
                               QueryRecordOptions options = QueryRecordOption::Default);

    /*! @overload
     Uses a KDbQuerySchema object. */
    tristate querySingleRecord(KDbQuerySchema* query, KDbRecordData* data,
                               QueryRecordOptions options = QueryRecordOption::Default);

    /*! @overload
     Accepts @a params as parameters that will be inserted into places marked with "[]" before
     query execution. */
    tristate querySingleRecord(KDbQuerySchema *query, KDbRecordData *data,
                               const QList<QVariant> &params,
                               QueryRecordOptions options = QueryRecordOption::Default);

    /*! Executes query for a raw statement @a sql and stores first record's field's
     (number @a column) string value inside @a value.
     For efficiency it's recommended that a query defined by @a sql
     should have just one field (SELECT one_field FROM ....).
     If @a options includes AddLimitTo1 value, "LIMIT 1" clause is added to the query (this is the default).
     Caller should make sure it is not there in the @a sql already.
     @return @c true if query was successfully executed and first record has been found,
     @c false on data retrieving failure, and @c cancelled if there's no single record available.
     @see queryStringList() */
    tristate querySingleString(const KDbEscapedString& sql, QString* value, int column = 0,
                               QueryRecordOptions options = QueryRecordOption::Default);

    /*! @overload
     Uses a KDbQuerySchema object. */
    tristate querySingleString(KDbQuerySchema* query, QString* value, int column = 0,
                               QueryRecordOptions options = QueryRecordOption::Default);

    /*! @overload
     Accepts @a params as parameters that will be inserted into places marked with [] before
     query execution. */
    tristate querySingleString(KDbQuerySchema* query, QString* value,
                               const QList<QVariant>& params, int column = 0,
                               QueryRecordOptions options = QueryRecordOption::Default);

    /*! Convenience function: executes query for a raw SQL statement @a sql and stores first
     record's field's (number @a column) value inside @a number. @see querySingleString().
     If @a options includes AddLimitTo1 value, "LIMIT 1" clause is added to the query (this is the default).
     Caller should make sure it is not there in the @a sql already.
     @return true if query was successfully executed and first record has been found,
     false on data retrieving failure, and cancelled if there's no single record available. */
    tristate querySingleNumber(const KDbEscapedString& sql, int* number, int column = 0,
                               QueryRecordOptions options = QueryRecordOption::Default);

    /*! @overload
     Uses a KDbQuerySchema object. */
     tristate querySingleNumber(KDbQuerySchema* query, int* number, int column = 0,
                                QueryRecordOptions options = QueryRecordOption::Default);

    /*! @overload
     Accepts @a params as parameters that will be inserted into places marked with "[]" before
     query execution. */
    tristate querySingleNumber(KDbQuerySchema* query, int* number,
                               const QList<QVariant>& params, int column = 0,
                               QueryRecordOptions options = QueryRecordOption::Default);

    /*! Executes query for a raw SQL statement @a sql and stores Nth field's string value
     of every record inside @a list, where N is equal to @a column. The list is initially cleared.
     For efficiency it's recommended that a query defined by @a sql
     should have just one field (SELECT one_field FROM ....).
     @return true if all values were fetched successfuly,
     false on data retrieving failure. Returning empty list can be still a valid result.
     On errors, the list is not cleared, it may contain a few retrieved values. */
    bool queryStringList(const KDbEscapedString& sql, QStringList* list, int column = 0);

    /*! @overload
     Uses a QuerySchema object. */
    bool queryStringList(KDbQuerySchema* query, QStringList* list, int column = 0);

    /*! @overload
     Accepts @a params as parameters that will be inserted into places marked with "[]" before
     query execution. */
    bool queryStringList(KDbQuerySchema* query, QStringList* list,
                         const QList<QVariant>& params, int column = 0);

    /*! @return @c true if there is at least one record has been returned by executing query
     for a raw SQL statement @a sql or @c false if no such record exists.
     If @a options includes AddLimitTo1 value, the query is optimized into "SELECT 1 FROM (sql) LIMIT 1"
     (this is the default). Caller should make sure "SELECT 1" and "LIMIT 1" is not there in the
     @a sql already.
     This method does not fetch any records. On error returns @c cancelled. */
    tristate resultExists(const KDbEscapedString &sql,
                          QueryRecordOptions options = QueryRecordOption::Default);

    /*! @return true if there is at least one record in @a table. */
    tristate isEmpty(KDbTableSchema* table);

    /**
     * @brief Return recently used SQL string
     *
     * If there was a successful query execution it is equal to result().sql(),
     * otherwise it is equal to result().errorSql().
     */
    virtual KDbEscapedString recentSqlString() const;

    //PROTOTYPE:
#define A , const QVariant&
#define H_INS_REC(args) QSharedPointer<KDbSqlResult> insertRecord(KDbTableSchema* tableSchema args)
#define H_INS_REC_ALL \
    H_INS_REC(A); \
    H_INS_REC(A A); \
    H_INS_REC(A A A); \
    H_INS_REC(A A A A); \
    H_INS_REC(A A A A A); \
    H_INS_REC(A A A A A A); \
    H_INS_REC(A A A A A A A); \
    H_INS_REC(A A A A A A A A)
    H_INS_REC_ALL;

#undef H_INS_REC
#define H_INS_REC(args) QSharedPointer<KDbSqlResult> insertRecord(KDbFieldList* fields args)

    H_INS_REC_ALL;
#undef H_INS_REC_ALL
#undef H_INS_REC
#undef A

    QSharedPointer<KDbSqlResult> insertRecord(KDbTableSchema *tableSchema,
                                              const QList<QVariant> &values);

    QSharedPointer<KDbSqlResult> insertRecord(KDbFieldList *fields, const QList<QVariant> &values);

    //! Options for creating table
    //! @since 3.1
    enum class CreateTableOption {
        Default = 0,
        DropDestination = 1 //!< Drop destination table if exists
    };
    Q_DECLARE_FLAGS(CreateTableOptions, CreateTableOption)

    /**
     * @brief Creates a new table
     *
     * Creates a new table defined by @a tableSchema. @c true is returned on success. In this case
     * @a tableSchema object is added to KDbConnection's structures and becomes owned the
     * KDbConnection object, so should not be destroyed by hand.
     *
     * If @a options include the DropDestination value and table schema with the same name as @a
     * tableSchema exists, it is dropped and the original identifier of the dropped schem is
     * assigned to the @a tableSchema object.
     *
     * If @a options do not include the DropDestination value and table schema with the same name
     * as @a tableSchema exists, @c false is returned.
     *
     * Table and column definitions are added to "Kexi system" tables.
     *
     * Prior to dropping the method checks if the table for the schema is in use, and if the new
     * schema defines at least one column.
     *
     * Note that on error:
     * - @a tableSchema is not inserted into KDbConnection's structures, so caller is still owner
     *   of the object,
     * - existing table schema object is not destroyed (e.g. it is still available for
     *   KDbConnection::tableSchema(const QString&), even if the table was physically dropped.
     *
     * @return true on success.
     */
    bool createTable(KDbTableSchema *tableSchema,
                     CreateTableOptions options = CreateTableOption::Default);

    /*! Creates a copy of table schema defined by @a tableSchema with data.
     Name, caption and description will be copied from @a newData.
     @return a table schema object. It is inserted into the KDbConnection structures
     and is owned by the KDbConnection object. The created table schema object should not
     be destroyed by hand afterwards.
     0 is returned on failure. Table with destination name must not exist.
     @see createTable() */
    KDbTableSchema *copyTable(const KDbTableSchema &tableSchema, const KDbObject &newData);

    /*! It is a convenience function, does exactly the same as
     KDbTableSchema *copyTable(const KDbTableSchema&, const KDbObject&). */
    KDbTableSchema *copyTable(const QString& tableName, const KDbObject &newData);

    /*! Drops a table defined by @a tableSchema (both table object as well as physically).
     If true is returned, schema information @a tableSchema is destoyed
     (because it's owned), so don't keep this anymore!
     No error is raised if the table does not exist physically
     - its schema is removed even in this case.

     Removes the table and column definitions in kexi__* "system schema" tables.
     First checks that the table is not a system table.

     @todo Check that a database is currently in use? (c.f. createTable)
     @todo Update any structure (e.g. query) that depends on this table */
    tristate dropTable(KDbTableSchema* tableSchema);

    /*! @overload
     * It is a convenience function.
     */
    tristate dropTable(const QString& tableName);

    /*! Alters @a tableSchema using @a newTableSchema in memory and on the db backend.
     @return true on success, cancelled if altering was cancelled. */
//! @todo (js): implement real altering
//! @todo (js): update any structure (e.g. query) that depend on this table!
    tristate alterTable(KDbTableSchema* tableSchema, KDbTableSchema* newTableSchema);

    //! Options for altering table name
    //! @since 3.1
    enum class AlterTableNameOption {
        Default = 0,
        DropDestination = 1 //!< Drop destination table if exists
    };
    Q_DECLARE_FLAGS(AlterTableNameOptions, AlterTableNameOption)

    /**
     * @brief Alters name of table
     *
     * Alters name of table described by @a tableSchema to @a newName.
     * If @a options include the DropDestination value and table having name @a newName already
     * exists, it is physically dropped, removed from connection's list of tables  and replaced
     * by @a tableSchema. In this case identifier of @a tableSchema is set to the dropped table's
     * identifier. This can be useful if @a tableSchema was created with a temporary name and
     * identifier. It is for example used in KDbAlterTableHandler.
     *
     * If @a options do not include the DropDestination value (the default) and table having name
     * @a newName already exists, @c false is returned and @c ERR_OBJECT_EXISTS error is set in
     * the connection object.
     *
     * Table name in the schema of @a tableSchema is updated on successful altering.
     * @return true on success.
     */
    bool alterTableName(KDbTableSchema* tableSchema, const QString& newName,
                        AlterTableNameOptions options = AlterTableNameOption::Default);

    /*! Drops a query defined by @a querySchema.
     If true is returned, schema information @a querySchema is destoyed
     (because it's owned), so don't keep this anymore!
    */
    bool dropQuery(KDbQuerySchema* querySchema);

    /*! It is a convenience function, does exactly the same as
     bool dropQuery( KDbQuerySchema* querySchema ) */
    bool dropQuery(const QString& queryName);

    /*! Removes information about object with @a objId
     from internal "kexi__object" and "kexi__objectdata" tables.
     @return true on success. */
    bool removeObject(int objId);

    /*! @return first field from @a fieldlist that has system name,
     @c nullptr if there are no such field.
     For checking, KDbDriver::isSystemFieldName() is used, so this check can
     be driver-dependent. */
    KDbField* findSystemFieldName(const KDbFieldList& fieldlist);

    /*! @return name of any (e.g. first found) database for this connection.
     This method does not close or open this connection. The method can be used
     (it is also internally used, e.g. for database dropping) when we need
     a database name before we can connect and execute any SQL statement
     (e.g. DROP DATABASE).

     The method can return nul lstring, but in this situation no automatic (implicit)
     connections could be made, what is useful by e.g. dropDatabase().

     Note for driver developers: return here a name of database which you are sure
     is existing.
     Default implementation returns:
     - value that previously had been set using setAvailableDatabaseName() for
       this connection, if it is not empty
     - else (2nd priority): value of KDbDriverBehavior::ALWAYS_AVAILABLE_DATABASE_NAME
     if it is not empty.

     See description of KDbDriverBehavior::ALWAYS_AVAILABLE_DATABASE_NAME member.
     You may want to reimplement this method only when you need to depend on
     this connection specifics
     (e.g. you need to check something remotely).
    */
    virtual QString anyAvailableDatabaseName();

    /*! Sets @a dbName as name of a database that can be accessible.
     This is option that e.g. application that make use of KDb library can set
     to tune connection's behavior when it needs to temporary connect to any database
     in the server to do some work.
     You can pass empty dbName - then anyAvailableDatabaseName() will try return
     KDbDriverBehavior::ALWAYS_AVAILABLE_DATABASE_NAME (the default) value
     instead of the one previously set with setAvailableDatabaseName().

     @see anyAvailableDatabaseName()
    */
    void setAvailableDatabaseName(const QString& dbName);

    /*! Because some engines need to have opened any database before
     executing administrative SQL statements like "create database" or "drop database",
     this method is used to use appropriate, existing database for this connection.
     For file-based db drivers this always return true and does not set @a name
     to any value. For other db drivers: this sets @a name to db name computed
     using anyAvailableDatabaseName(), and if the name computed is empty, false
     is returned; if it is not empty, useDatabase() is called.
     False is returned also when useDatabase() fails.
     You can call this method from your application's level if you really want to perform
     tasks that require any used database. In such a case don't forget
     to closeDatabase() if returned @a name is not empty.

     Note: This method has nothing to do with creating or using temporary databases
     in such meaning that these database are not persistent
    */
    bool useTemporaryDatabaseIfNeeded(QString* name);

    /**
     * Prepares execution of a new native (raw, backend-specific) SQL query.
     *
     * The query is described by a raw statement @a sql which should be is valid and properly
     * escaped. Access to results can be obtained using
     * the returned KDbSqlResult object. The object is guarded with a shared pointer to facilitate
     * transfer of ownership and memory management. A null pointer is returned if preparation of
     * the query fails. Use KDbConnection::result() immediately after calling prepareSql() to
     * obtain detailed result information about the preparation.
     *
     * The returned object should be deleted before the database connection is closed.
     * Connection object does not deletes the KDbSqlResult objects. It is also possible and
     * recommended that caller deletes the KDbSqlResult object as soon as the result is not needed.
     *
     * The returned object can be ignored if the query is not supposed to return records (e.g.
     * manipulates data through INSERT, UPDATE, DELETE, ...) or the caller is not interested in the
     * records. Thanks to the use of the shared pointer the object will be immediately deleted and
     * execution will be finalized prior to that. However to execute queries that return no
     * results, executeSql() is a better choice because of performance and easier reporting to
     * results.
     *
     * @note Only use this method if a non-portable raw query is required.
     *       In other cases use prepareQuery() or executeQuery() and the KDbCursor object.
     */
    QSharedPointer<KDbSqlResult> prepareSql(const KDbEscapedString& sql) Q_REQUIRED_RESULT;

    /**
     * Executes a new native (raw, backend-specific) SQL query
     *
     * The query is described by a raw statement @a sql which should be is valid and properly
     * escaped. This method is a convenience version of prepareSql() that immediately starts and
     * finalizes execution of a raw query in one step and provides a result. Use it for queries
     * that do not return records, i.e. for queries that manipulate data (INSERT, UPDATE, DELETE,
     * ...) or if the caller is not interested in the returned records.
     *
     * @note Only use this method if a non-portable raw query is required.
     *       In other cases use prepareQuery() or executeQuery() and the KDbCursor object.
     */
    bool executeSql(const KDbEscapedString& sql);

    /*! Stores object (id, name, caption, description)
    described by @a object on the backend. It is expected that entry on the
    backend already exists, so it's updated. Changes to identifier attribute are not allowed.
    @return true on success. */
    bool storeObjectData(KDbObject* object);

    /*! Stores new entry for object (id, name, caption, description)
    described by @a object on the backend. If object.id() was less than 0,
    new, unique object identifier is obtained and assigned to @a object (see KDbObject::id()).
    @return true on success. */
    bool storeNewObjectData(KDbObject* object);

    /*! Finds object data for object of type @a type and identifier @a id.
     Added for convenience.
     If @a type is KDb::AnyObjectType, object type is ignored during the find.
     @see setupObjectData(const KDbRecordData*, KDbObject*).
     @return true on success, false on failure and cancelled when such object couldn't be found.
     @since 3.1
    */
    tristate loadObjectData(int type, int id, KDbObject* object);

    /*! Finds object data for object of type @a type and name @a name.
     If the object is found, resulted schema is stored in @a object and true is returned,
     otherwise false is returned. */
    tristate loadObjectData(int type, const QString& name, KDbObject* object);

    /*! Loads (potentially large) data block (e.g. xml form's representation), referenced by objectID
     and puts it to @a dataString. The can be block indexed with optional @a dataID.
     @return true on success, false on failure and cancelled when there is no such data block
     @see storeDataBlock(). */
    tristate loadDataBlock(int objectID, QString* dataString, const QString& dataID = QString());

    /*! Stores (potentially large) data block @a dataString (e.g. xml form's representation),
     referenced by objectID. Block will be stored in "kexi__objectdata" table and
     an optional @a dataID identifier.
     If there is already such record in the table, it's simply overwritten.
     @return true on success
     @see loadDataBlock() removeDataBlock() copyDataBlock(). */
    bool storeDataBlock(int objectID, const QString &dataString,
                        const QString& dataID = QString());

    /*! Copies (potentially large) data, e.g. form's XML representation,
     referenced by @a sourceObjectID pointed by optional @a dataID.
     @return true on success. Does not fail if blocks do not exist.
     Prior to copying, existing data blocks are removed even if there are no new blocks to copy.
     Copied data blocks will have @a destObjectID object identifier assigned.
     Note that if @a dataID is not specified, all data blocks found for the @a sourceObjectID
     will be copied.
     @see loadDataBlock() storeDataBlock() removeDataBlock(). */
    bool copyDataBlock(int sourceObjectID, int destObjectID, const QString& dataID = QString());

    /*! Removes (potentially large) string data (e.g. xml form's representation),
     referenced by @a objectID, and pointed by optional @a dataID.
     @return true on success. Does not fail if the block does not exist.
     Note that if @a dataID is not specified, all data blocks for the @a objectID will be removed.
     @see loadDataBlock() storeDataBlock() copyDataBlock(). */
    bool removeDataBlock(int objectID, const QString& dataID = QString());

    /*! Prepare an SQL statement and return a @a KDbPreparedStatement instance. */
    KDbPreparedStatement prepareStatement(KDbPreparedStatement::Type type,
        KDbFieldList* fields, const QStringList& whereFieldNames = QStringList());

    bool isInternalTableSchema(const QString& tableName);

    /**
     * @brief Returns number of records returned by given SQL statement
     *
     * @return number of records that can be retrieved after executing @a sql statement within
     * a connection @a conn. The statement should be of type SELECT. For SQL data sources it does not
     * fetch any records, only "COUNT(*)" SQL aggregation is used at the backed.
     * -1 is returned if any error occurred or if @a conn is @c nullptr.
     *
     * @since 3.1
     */
    //! @todo perhaps use quint64 here?
    int recordCount(const KDbEscapedString& sql);

    /**
     * @brief Returns number of records that contains given table
     *
     * @return number of records that can be retrieved from @a tableSchema.
     * To obtain the result the table must be created or retrieved using a KDbConnection object,
     * i.e. tableSchema.connection() must not return @c nullptr. For SQL data sources only "COUNT(*)"
     * SQL aggregation is used at the backed.
     * -1 is returned if error occurred or if tableSchema.connection() is @c nullptr.
     *
     * @since 3.1
     */
    //! @todo perhaps use quint64 here?
    //! @todo does not work with non-SQL data sources
    int recordCount(const KDbTableSchema& tableSchema);

    /**
     * @overload
     *
     * Operates on a query schema. @a params are optional values of parameters that will be inserted
     * into [] placeholders before execution of query that counts the records.
     * To obtain the result the query must be created or retrieved using a KDbConnection object,
     * i.e. querySchema->connection() must not return @c nullptr. For SQL data sources only "COUNT(*)"
     * SQL aggregation is used at the backed.
     * -1 is returned if error occurred or if querySchema->connection() is @c nullptr.
     *
     * @since 3.1
     */
    //! @todo perhaps use quint64 here?
    int recordCount(KDbQuerySchema* querySchema,
                               const QList<QVariant>& params = QList<QVariant>());

    /**
     * @overload
     *
     * Operates on a table or query schema. @a params is a list of optional parameters that
     * will be inserted into [] placeholders before execution of query that counts the records.
     *
     * If @a tableOrQuery is @c nullptr or provides neither table nor query, -1 is returned.
     *
     * @since 3.1
     */
    //! @todo perhaps use quint64 here?
    int recordCount(KDbTableOrQuerySchema* tableOrQuery,
                               const QList<QVariant>& params = QList<QVariant>());

    //! Identifier escaping function in the associated KDbDriver.
    /*! Calls the identifier escaping function in this connection to
     escape table and column names.  This should be used when explicitly
     constructing SQL strings (e.g. "FROM " + escapeIdentifier(tablename)).
     It should not be used for other functions (e.g. don't do
     useDatabase(escapeIdentifier(database))), because the identifier will
     be escaped when the called function generates, for example, "USE " +
     escapeIdentifier(database).

     For efficiency, KDb "system" tables (prefixed with kexi__)
     and columns therein are not escaped - we assume these are valid identifiers for all drivers.

     Use KDbEscapedString::isValid() to check if escaping has been performed successfully.
     Invalid strings are set to null in addition, that is KDbEscapedString::isNull() is true,
     not just isEmpty().
    */
    virtual QString escapeIdentifier(const QString& id) const;

protected:
    /*! Used by KDbDriver */
    KDbConnection(KDbDriver *driver, const KDbConnectionData& connData,
                  const KDbConnectionOptions &options);

    /*! Method to be called form KDbConnection's subclass destructor.
     @see ~KDbConnection() */
    void destroy();

    /*! For implementation: connects to database.
      @return true on success. */
    virtual bool drv_connect() = 0;

    /*! For implementation: disconnects database
      @return true on success. */
    virtual bool drv_disconnect() = 0;

    /*! For implementation: Sets @a version to real server's version.
     Depending on backend type this method is called after
     (if KDbDriverBehavior::USING_DATABASE_REQUIRED_TO_CONNECT is true)
     or before database is used
     (if KDbDriverBehavior::USING_DATABASE_REQUIRED_TO_CONNECT is false),
     i.e. for PostgreSQL it is called after.
     In any case it is called after successful drv_connect().
     @return true on success. */
    virtual bool drv_getServerVersion(KDbServerVersionInfo* version) = 0;

    /*! LOW LEVEL METHOD. For implementation: returns true if table
     with name @a tableName exists in the database.
     @return @c false if it does not exist or @c cancelled if error occurred.
     The lookup is case insensitive. */
    virtual tristate drv_containsTable(const QString &tableName) = 0;

    /**
     * Creates table using @a tableSchema information.
     *
     * @return true on success.
     *
     * Default implementation builds a statement using createTableStatement() and calls
     * executeSql(). Note for driver developers: reimplement this only to perform creation in other
     * way.
     */
    virtual bool drv_createTable(const KDbTableSchema& tableSchema);

    /*! Alters table's described @a tableSchema name to @a newName.
     This is the default implementation, using "ALTER TABLE <oldname> RENAME TO <newname>",
     what's supported by SQLite >= 3.2, PostgreSQL, MySQL.
     Backends lacking ALTER TABLE, for example SQLite, reimplement this with by an inefficient
     data copying to a new table. In any case, renaming is performed at the backend.
     It's good idea to keep the operation within a transaction.
     @return true on success. */
    virtual bool drv_alterTableName(KDbTableSchema* tableSchema, const QString& newName);

    /*! Copies table data from @a tableSchema to @a destinationTableSchema
     Default implementation executes "INSERT INTO .. SELECT * FROM .."
     @return true on success. */
    virtual bool drv_copyTableData(const KDbTableSchema &tableSchema,
                                   const KDbTableSchema &destinationTableSchema);

    /*! Physically drops table named with @a name.
     Default impelmentation executes "DROP TABLE.." command,
     so you rarely want to change this. */
    virtual bool drv_dropTable(const QString& tableName);

    /*! @internal drops table @a tableSchema physically, but destroys
     @a tableSchema object only if @a alsoRemoveSchema is true.
     Used (alsoRemoveSchema==false) on table altering:
     if recreating table can fail we're giving up and keeping
     the original table schema (even if it is no longer points to any real data). */
    tristate dropTableInternal(KDbTableSchema* tableSchema, bool alsoRemoveSchema);

    /*! Setups data for object that owns @a object (e.g. table, query)
      opened on 'kexi__objects' table, pointing to a record
      corresponding to given object. */
    bool setupObjectData(const KDbRecordData& data, KDbObject* object);

    /*! @return a new field table schema for a table retrieved from @a data.
     Ownership of the returned object is passed to the caller.
     Used internally by tableSchema(). */
    KDbField* setupField(const KDbRecordData& data) Q_REQUIRED_RESULT;

    /**
     * Prepares query for a raw SQL statement @a sql with possibility of returning records.
     *
     * It is useful mostly for SELECT queries. While INSERT queries do not return records, the
     * KDbSqlResult object offers KDbSqlResult::lastInsertRecordId(). The @sql should be is valid
     * and properly escaped. Only use this method if you really need. For low-level access to the
     * results (without cursors). The result may be not stored (not buffered) yet. Use
     * KDbSqlResult::fetchRecord() to fetch each record. @return Null pointer if there is no proper
     * result or error. Ownership of the returned object is passed to the caller.
     *
     * @see prepareSql
     */
    virtual KDbSqlResult* drv_prepareSql(const KDbEscapedString &sql) /*Q_REQUIRED_RESULT*/ = 0;

    /**
     * Executes query for a raw SQL statement @a sql without returning resulting records.
     *
     * It is useful mostly for INSERT queries but it is possible to execute SELECT queries when
     * returned records can be ignored. The @sql should be is valid and properly escaped.
     *
     * @note Only use this method if you really need.
     * @see executeSql
     */
    virtual bool drv_executeSql(const KDbEscapedString& sql) = 0;

    /*! For reimplementation: loads list of databases' names available for this connection
     and adds these names to @a list. If your server is not able to offer such a list,
     consider reimplementing drv_databaseExists() instead.
     The method should return true only if there was no error on getting database names
     list from the server.
     Default implementation puts empty list into @a list and returns true.
     @see databaseNames */
    virtual bool drv_getDatabasesList(QStringList* list);

    /*! For optional reimplementation: asks server if database @a dbName exists.
     This method is used internally in databaseExists(). The default  implementation
     calls databaseNames and checks if that list contains @a dbName. If you need to
     ask the server specifically if a database exists, eg. if you can't retrieve a list
     of all available database names, please reimplement this method and do all
     needed checks.

     See databaseExists() description for details about ignoreErrors argument.
     You should use it properly in your implementation.

     Note: This method should also work if there is already database used (with useDatabase());
     in this situation no changes should be made in current database selection. */
    virtual bool drv_databaseExists(const QString &dbName, bool ignoreErrors = true);

    /*! For implementation: creates new database using connection */
    virtual bool drv_createDatabase(const QString &dbName = QString()) = 0;

    /*! For implementation: opens existing database using connection
     @return true on success, false on failure; sets @a cancelled to true if this action
     has been cancelled. */
    virtual bool drv_useDatabase(const QString &dbName = QString(), bool *cancelled = nullptr,
                                 KDbMessageHandler* msgHandler = nullptr) = 0;

    /*! For implementation: closes previously opened database
      using connection. */
    virtual bool drv_closeDatabase() = 0;

    /*! @return true if internal driver's structure is still in opened/connected
     state and database is used.
     Note for driver developers: Put here every test that you can do using your
     internal engine's database API,
     eg (a bit schematic):  my_connection_struct->isConnected()==true.
     Do not check things like KDbConnection::isDatabaseUsed() here or other things
     that "KDb already knows" at its level.
     If you cannot test anything, just leave default implementation (that returns true).

     Result of this method is used as an additional chance to check for isDatabaseUsed().
     Do not call this method from your driver's code, it should be used at KDb level only.
    */
    virtual bool drv_isDatabaseUsed() const {
        return true;
    }

    /*! For implementation: drops database from the server
      using connection. After drop, database shouldn't be accessible
      anymore. */
    virtual bool drv_dropDatabase(const QString &dbName = QString()) = 0;

    /*!
     Creates table named by @a tableName. Schema object must be on
     schema tables' list before calling this method (otherwise false if returned).
     Just uses drv_createTable( const KDbTableSchema& tableSchema ).
     Used internally, e.g. in createDatabase().
     @return true on success
    */
    virtual bool drv_createTable(const QString& tableName);

    /*! Note for driver developers: begins new transaction
     and returns handle to it. Default implementation just
     executes "BEGIN" sql statement and returns just empty data (KDbTransactionData object).
     Ownership of the returned object is passed to the caller.

     Drivers that do not support transactions (see KDbDriver::features())
     do never call this method.
     Reimplement this method if you need to do something more
     (e.g. if you driver will support multiple transactions per connection).
     Make subclass of KDbTransactionData (declared in KDbTransaction.h)
     and return object of this subclass.
     @c nullptr should be returned on error.
     Do not check anything in connection (isConnected(), etc.) - all is already done.

     @todo Add support for nested transactions,
           e.g. KDbTransactionData* beginTransaction(KDbTransactionData *parent)
    */
    virtual KDbTransactionData* drv_beginTransaction() Q_REQUIRED_RESULT;

    /*! Note for driver developers: begins new transaction
     and returns handle to it. Default implementation just
     executes "COMMIT" sql statement and returns true on success.

     @see drv_beginTransaction()
    */
    virtual bool drv_commitTransaction(KDbTransactionData* trans);

    /*! Note for driver developers: begins new transaction
     and returns handle to it. Default implementation just
     executes "ROLLBACK" sql statement and returns true on success.

     @see drv_beginTransaction()
    */
    virtual bool drv_rollbackTransaction(KDbTransactionData* trans);


    /*! Preprocessing (if any) required by drivers before execution of an
        Insert statement.
        Reimplement this method in your driver if there are any special processing steps to be
        executed before an Insert statement.
      @see drv_afterInsert()
    */
    virtual bool drv_beforeInsert(const QString& tableName, KDbFieldList* fields) {
        Q_UNUSED(tableName);
        Q_UNUSED(fields);
        return true;
    }

    /*! Postprocessing (if any) required by drivers before execution of an
        Insert statement.
        Reimplement this method in your driver if there are any special processing steps to be
        executed after an Insert statement.
      @see drv_beforeInsert()
    */
    virtual bool drv_afterInsert(const QString& tableName, KDbFieldList* fields) {
        Q_UNUSED(tableName);
        Q_UNUSED(fields);
        return true;
    }

    /*! Preprocessing required by drivers before execution of an
        Update statement.
        Reimplement this method in your driver if there are any special processing steps to be
        executed before an Update statement.
    @see drv_afterUpdate()
    */
    virtual bool drv_beforeUpdate(const QString& tableName, KDbFieldList* fields) {
        Q_UNUSED(tableName);
        Q_UNUSED(fields);
        return true;
    }

    /*! Postprocessing required by drivers before execution of an
        Insert statement.
        Reimplement this method in your driver if there are any special processing steps to be
        executed after an Update statement.
      @see drv_beforeUpdate()
    */
    virtual bool drv_afterUpdate(const QString& tableName, KDbFieldList* fields) {
        Q_UNUSED(tableName);
        Q_UNUSED(fields);
        return true;
    }

    /*! Changes autocommiting option for established connection.
      @return true on success.

      Note for driver developers: reimplement this only if your engine
      allows to set special auto commit option (like "SET AUTOCOMMIT=.." in MySQL).
      If not, auto commit behavior will be simulated if at least single
      transactions per connection are supported by the engine.
      Do not set any internal flags for autocommiting -- it is already done inside
      setAutoCommit().

      Default implementation does nothing with connection, just returns true.

      @see drv_beginTransaction(), autoCommit(), setAutoCommit()
     */
    virtual bool drv_setAutoCommit(bool on);

    /*! Prepare an SQL statement and return a @a KDbPreparedStatementInterface-derived object.
     Ownership of the returned object is passed to the caller. */
    virtual KDbPreparedStatementInterface* prepareStatementInternal() /*Q_REQUIRED_RESULT*/ = 0;

    /*! Internal, for handling autocommited transactions:
     begins transaction if one is supported.
     @return true if new transaction started
     successfully or no transactions are supported at all by the driver
     or if autocommit option is turned off.
     A handle to a newly created transaction (or @c nullptr on error) is passed
     to @a tg parameter.

     Special case when used database driver has only single transaction support
     (KDbDriver::SingleTransactions):
     and there is already transaction started, it is committed before
     starting a new one, but only if this transaction has been started inside KDbConnection object.
     (i.e. by beginAutoCommitTransaction()). Otherwise, a new transaction will not be started,
     but true will be returned immediately.
    */
    bool beginAutoCommitTransaction(KDbTransactionGuard* tg);

    /*! Internal, for handling autocommited transactions:
     Commits transaction prevoiusly started with beginAutoCommitTransaction().
     @return true on success or when no transactions are supported
     at all by the driver.

     Special case when used database driver has only single transaction support
     (KDbDriver::SingleTransactions): if @a trans has been started outside KDbConnection object
     (i.e. not by beginAutoCommitTransaction()), the transaction will not be committed.
    */
    bool commitAutoCommitTransaction(const KDbTransaction& trans);

    /*! Internal, for handling autocommited transactions:
     Rolls back transaction prevoiusly started with beginAutoCommitTransaction().
     @return true on success or when no transactions are supported
     at all by the driver.

     Special case when used database driver has only single transaction support
     (KDbDriver::SingleTransactions): @a trans will not be rolled back
     if it has been started outside this KDbConnection object.
    */
    bool rollbackAutoCommitTransaction(const KDbTransaction& trans);

    /*! Helper: checks if connection is established;
      if not: error message is set up and false returned */
    bool checkConnected();

    /*! Helper: checks both if connection is established and database any is used;
      if not: error message is set up and false returned */
    bool checkIsDatabaseUsed();

    /*! Update a record. */
    bool updateRecord(KDbQuerySchema* query, KDbRecordData* data, KDbRecordEditBuffer* buf, bool useRecordId = false);
    /*! Insert a new record. */
    bool insertRecord(KDbQuerySchema* query, KDbRecordData* data, KDbRecordEditBuffer* buf, bool getRecordId = false);
    /*! Delete an existing record. */
    bool deleteRecord(KDbQuerySchema* query, KDbRecordData* data, bool useRecordId = false);
    /*! Delete all existing records. */
    bool deleteAllRecords(KDbQuerySchema* query);

    /*! Called by KDbTableSchema -- signals destruction to KDbConnection object
     To avoid having deleted table object on its list. */
    void removeMe(KDbTableSchema *ts);

    // -- internal methods follow

    /*! @internal
     @return true if the cursor @a cursor contains column @a column,
     else, sets appropriate error with a message and returns false. */
    bool checkIfColumnExists(KDbCursor *cursor, int column);

    /*! @internal used by insertRecord() methods. */
    QSharedPointer<KDbSqlResult> insertRecordInternal(const QString &tableSchemaName,
                                                      KDbFieldList *fields,
                                                      const KDbEscapedString &sql);

    /*! @internal used by querySingleRecord() methods. */
    tristate querySingleRecordInternal(KDbRecordData* data, const KDbEscapedString* sql,
                                       KDbQuerySchema* query, const QList<QVariant>* params,
                                       QueryRecordOptions options);

    /*! @internal used by querySingleString() methods. */
    tristate querySingleStringInternal(const KDbEscapedString* sql, QString* value,
                                       KDbQuerySchema* query, const QList<QVariant>* params,
                                       int column, QueryRecordOptions options);

    /*! @internal used by queryNumberString() methods. */
    tristate querySingleNumberInternal(const KDbEscapedString* sql, int* number,
                                       KDbQuerySchema* query, const QList<QVariant>* params,
                                       int column, QueryRecordOptions options);

    /*! @internal used by queryStringList() methods. */
    bool queryStringListInternal(const KDbEscapedString *sql, QStringList* list,
                                 KDbQuerySchema* query, const QList<QVariant>* params,
                                 int column, bool (*filterFunction)(const QString&));

    /*! @internal used by *Internal() methods.
     Executes query based on a raw SQL statement @a sql or @a query with optional @a params.
     Ownership of the returned object is passed to the caller.*/
    KDbCursor* executeQueryInternal(const KDbEscapedString& sql, KDbQuerySchema* query,
                                    const QList<QVariant>* params) Q_REQUIRED_RESULT;

    /*! Loads extended schema information for table @a tableSchema,
     if present (see ExtendedTableSchemaInformation in Kexi Wiki).
     @return true on success */
    bool loadExtendedTableSchemaData(KDbTableSchema* tableSchema);

    /*! Stores extended schema information for table @a tableSchema,
     (see ExtendedTableSchemaInformation in Kexi Wiki).
     The action is performed within the current transaction,
     so it's up to you to commit.
     Used, e.g. by createTable(), within its transaction.
     @return true on success */
    bool storeExtendedTableSchemaData(KDbTableSchema* tableSchema);

    /*! @internal
     Stores main field's schema information for field @a field.
     Used in table altering code when information in kexi__fields has to be updated.
     @return true on success and false on failure. */
    bool storeMainFieldSchema(KDbField *field);

    //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    /*! This is a part of alter table interface implementing lower-level operations
     used to perform table schema altering. Used by KDbAlterTableHandler.

     Changes value of field property.
     @return true on success, false on failure, cancelled if the action has been cancelled.

     Note for driver developers: implement this if the driver has to supprot the altering. */
    virtual tristate drv_changeFieldProperty(KDbTableSchema* table, KDbField* field,
            const QString& propertyName, const QVariant& value) {
        Q_UNUSED(table); Q_UNUSED(field); Q_UNUSED(propertyName); Q_UNUSED(value);
        return cancelled;
    }

    //! Used by KDbCursor class
    void addCursor(KDbCursor* cursor);

    //! Used by KDbCursor class
    void takeCursor(KDbCursor* cursor);

private:
    //! Internal, used by storeObjectData(KDbObject*) and storeNewObjectData(KDbObject* object).
    bool storeObjectDataInternal(KDbObject* object, bool newObject);

    //! @internal
    //! @return identifier escaped by driver (if @a escapingType is KDb::DriverEscaping)
    //! or by the KDb's built-in escape routine.
    QString escapeIdentifier(const QString& id, KDb::IdentifierEscapingType escapingType) const;

    KDbConnectionPrivate* d; //!< @internal d-pointer class.

    Q_DISABLE_COPY(KDbConnection)
    friend class KDbConnectionPrivate;
    friend class KDbAlterTableHandler;
    friend class KDbConnectionProxy;
    friend class KDbCursor;
    friend class KDbDriver;
    friend class KDbProperties; //!< for setError()
    friend class KDbQuerySchema;
    friend class KDbQuerySchemaPrivate;
    friend class KDbTableSchemaChangeListenerPrivate;
    friend class KDbTableSchema; //!< for removeMe()
};

Q_DECLARE_OPERATORS_FOR_FLAGS(KDbConnection::QueryRecordOptions)
Q_DECLARE_OPERATORS_FOR_FLAGS(KDbConnection::AlterTableNameOptions)
Q_DECLARE_OPERATORS_FOR_FLAGS(KDbConnection::CreateTableOptions)

#endif
