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/**
* This class allows to include a set of layers in a database-side transaction,
* provided the layer data providers support transactions and are compatible
* with each other.
*
* Only layers which are not in edit mode can be included in a transaction,
* and all layers need to be in read-only mode for a transaction to be committed
* or rolled back.
*
* Layers cannot only be included in one transaction at a time.
*
* When editing layers which are part of a transaction group, all changes are
* sent directly to the data provider (bypassing the undo/redo stack), and the
* changes can either be committed or rolled back on the database side via the
* QgsTransaction::commit and QgsTransaction::rollback methods.
*
* As long as the transaction is active, the state of all layer features reflects
* the current state in the transaction.
*
* Edits on features can get rejected if another conflicting transaction is active.
*/
class QgsTransaction : QObject /Abstract/
{
%TypeHeaderCode
#include <qgstransaction.h>
%End
public:
/** Creates a transaction for the specified connection string and provider */
static QgsTransaction* create( const QString& connString, const QString& providerKey ) /Factory/;
/** Creates a transaction which includes the specified layers. Connection string
* and data provider are taken from the first layer */
static QgsTransaction* create( const QStringList& layerIds ) /Factory/;
virtual ~QgsTransaction();
/** Add layer to the transaction. The layer must not be in edit mode.*/
bool addLayer( const QString& layerId );
/** Add layer to the transaction. The layer must not be in edit mode.*/
bool addLayer( QgsVectorLayer* layer );
/** Begin transaction
* The statement timeout, in seconds, specifies how long an sql statement
* is allowed to block QGIS before it is aborted. Statements can block,
* depending on the provider, if multiple transactions are active and a
* statement would produce a conflicting state. In these cases, the
* statements block until the conflicting transaction is committed or
* rolled back.
* Some providers might not honour the statement timeout. */
bool begin( QString& errorMsg /Out/, int statementTimeout = 20 );
/** Commit transaction. All layers need to be in read-only mode. */
bool commit( QString& errorMsg /Out/ );
/** Roll back transaction. All layers need to be in read-only mode. */
bool rollback( QString& errorMsg /Out/ );
/** Executes sql */
virtual bool executeSql( const QString& sql, QString& error /Out/ ) = 0;
/**
* Checks if a the provider of a give layer supports transactions.
*/
static bool supportsTransaction( const QgsVectorLayer* layer );
signals:
/**
* Emitted after a rollback
*/
void afterRollback();
};
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