UNIQUE fields detector for sqlite based providers

This is a temporary solution for OGR because we expect
to use the native GDAL implementation in GDAL 3.2.

For now a new method QgsSqliteUtils::uniqueFields
used by spatialite and OGR/GPKG is used to detect
UNIQUE constraints on single fields.

python/core/auto_generated/qgssqliteutils.sip.in

@@ -52,6 +52,21 @@ Returns a string list of SQLite (and spatialite) system tables
 
 .. versionadded:: 3.8
 %End
+
+    static QSet<QString> uniqueFields( sqlite3 *connection, const QString &tableName, QString &errorMessage );
+%Docstring
+Returns a list of field names for ``connection`` and ``tableName`` having a UNIQUE constraint,
+fields that are part of a UNIQUE constraint that spans over multiple fields
+are not returned.
+
+.. note::
+
+   the implementation is the same of GDAL but the test coverage is much
+   better in GDAL.
+
+.. versionadded:: 3.14
+%End
+
 };
 
 /************************************************************************

src/core/providers/ogr/qgsogrprovider.cpp

@@ -1105,13 +1105,15 @@ void QgsOgrProvider::loadFields()
 
   // This is a temporary solution until GDAL Unique support is available
   QSet<QString> uniqueFieldNames;
+
+
   if ( mGDALDriverName == QLatin1String( "GPKG" ) )
   {
     sqlite3_database_unique_ptr dsPtr;
-    if ( dsPtr.open( mFilePath ) == SQLITE_OK )
+    if ( dsPtr.open_v2( mFilePath, SQLITE_OPEN_READONLY, nullptr ) == SQLITE_OK )
     {
       QString errMsg;
-      uniqueFieldNames = dsPtr.uniqueFields( mOgrLayer->name(), errMsg );
+      uniqueFieldNames = QgsSqliteUtils::uniqueFields( dsPtr.get(), mOgrLayer->name(), errMsg );
       if ( ! errMsg.isEmpty() )
       {
         QgsMessageLog::logMessage( tr( "GPKG error searching for unique constraints on fields for table %1" ).arg( QString( mOgrLayer->name() ) ), tr( "OGR" ) );

src/core/qgssqliteutils.cpp

@@ -120,23 +120,23 @@ int sqlite3_database_unique_ptr::exec( const QString &sql, QString &errorMessage
   return ret;
 }
 
-QSet<QString> sqlite3_database_unique_ptr::uniqueFields( const QString &tableName, QString &errorMessage )
+QSet<QString> QgsSqliteUtils::uniqueFields( sqlite3 *connection, const QString &tableName, QString &errorMessage )
 {
   QSet<QString> uniqueFieldsResults;
   char *zErrMsg = 0;
   std::vector<std::string> rows;
-  QString sql = sqlite3_mprintf( "select sql from sqlite_master where type='table' and name=%q", QgsSqliteUtils::quotedIdentifier( tableName ).toStdString().c_str() );
+  QString sql = sqlite3_mprintf( "select sql from sqlite_master where type='table' and name=%q", quotedIdentifier( tableName ).toStdString().c_str() );
   auto cb = [ ](
               void *data /* Data provided in the 4th argument of sqlite3_exec() */,
               int /* The number of columns in row */,
               char **argv /* An array of strings representing fields in the row */,
-              char **/* An array of strings representing column names */ ) -> int
+              char ** /* An array of strings representing column names */ ) -> int
   {
     static_cast<std::vector<std::string>*>( data )->push_back( argv[0] );
     return 0;
   };
 
-  int rc = sqlite3_exec( get(), sql.toUtf8(), cb, ( void * )&rows, &zErrMsg );
+  int rc = sqlite3_exec( connection, sql.toUtf8(), cb, ( void * )&rows, &zErrMsg );
   if ( rc != SQLITE_OK )
   {
     errorMessage = zErrMsg;
@@ -172,7 +172,7 @@ QSet<QString> sqlite3_database_unique_ptr::uniqueFields( const QString &tableNam
   // Search indexes:
   sql = sqlite3_mprintf( "SELECT sql FROM sqlite_master WHERE type='index' AND"
                          " tbl_name='%q' AND sql LIKE 'CREATE UNIQUE INDEX%%'" );
-  rc = sqlite3_exec( get(), sql.toUtf8(), cb, ( void * )&rows, &zErrMsg );
+  rc = sqlite3_exec( connection, sql.toUtf8(), cb, ( void * )&rows, &zErrMsg );
   if ( rc != SQLITE_OK )
   {
     errorMessage = zErrMsg;

src/core/qgssqliteutils.h

@@ -154,15 +154,6 @@ class CORE_EXPORT sqlite3_database_unique_ptr : public std::unique_ptr< sqlite3,
      */
     int exec( const QString &sql, QString &errorMessage SIP_OUT ) const;
 
-    /**
-     * Returns a list of field names for \a tableName having a UNIQUE constraint,
-     * fields that are part of a UNIQUE constraint that spans over multiple fields
-     * are not returned.
-     * \note the implementation is the same of GDAL but the test coverage is much
-     *       better in GDAL.
-     * \since QGIS 3.14
-     */
-    QSet<QString> uniqueFields( const QString &tableName, QString &errorMessage );
 };
 
 /**
@@ -210,6 +201,17 @@ class CORE_EXPORT QgsSqliteUtils
      * \since QGIS 3.8
      */
     static QStringList systemTables();
+
+    /**
+     * Returns a list of field names for \a connection and \a tableName having a UNIQUE constraint,
+     * fields that are part of a UNIQUE constraint that spans over multiple fields
+     * are not returned.
+     * \note the implementation is the same of GDAL but the test coverage is much
+     *       better in GDAL.
+     * \since QGIS 3.14
+     */
+    static QSet<QString> uniqueFields( sqlite3 *connection, const QString &tableName, QString &errorMessage );
+
 };
 
 #endif // QGSSQLITEUTILS_H

src/providers/spatialite/qgsspatialiteprovider.cpp

@@ -913,15 +913,11 @@ void QgsSpatiaLiteProvider::fetchConstraints()
     // Use the same logic implemented in GDAL for GPKG
     QSet<QString> uniqueFieldNames;
     {
-      sqlite3_database_unique_ptr dsPtr;
+      QString errMsg;
-      if ( dsPtr.open( mSqlitePath ) == SQLITE_OK )
+      uniqueFieldNames = QgsSqliteUtils::uniqueFields( mSqliteHandle, mTableName, errMsg );
+      if ( ! errMsg.isEmpty() )
       {
-        QString errMsg;
+        QgsMessageLog::logMessage( tr( "Error searching for unique constraints on fields for table %1" ).arg( mTableName ), tr( "spatialite" ) );
-        uniqueFieldNames = dsPtr.uniqueFields( mTableName, errMsg );
-        if ( ! errMsg.isEmpty() )
-        {
-          QgsMessageLog::logMessage( tr( "Error searching for unique constraints on fields for table %1" ).arg( mTableName ), tr( "spatialite" ) );
-        }
       }
     }