Postgis: cache information about enum fields

This is called several times and can slow down substantially
the opening of the attribute table.

Partially fixes #21303  (down from ~30 to ~6 seconds on a remote
connection)

The remaining ~4 seconds (compared to ~2 seconds in 2.18) are due
to the check for enums and provider-side  constraints, that were
not implemented in 2.18.

See: QgsEnumerationWidgetFactory::fieldScore and the call to
enumValues for details, fieldScore is called several times
because QgsAttributeTableModel::loadAttributes is also
called multiple times and it queries for widget configuration
all the times.

Author: elpaso

src/providers/postgres/qgspostgresprovider.cpp

@@ -1683,42 +1683,50 @@ QStringList QgsPostgresProvider::uniqueStringsMatching( int index, const QString
 
 void QgsPostgresProvider::enumValues( int index, QStringList &enumList ) const
 {
-  enumList.clear();
 
   if ( index < 0 || index >= mAttributeFields.count() )
     return;
 
+  if ( ! mShared->fieldSupportsEnumValuesIsSet( index ) )
+  {
+    mShared->setFieldSupportsEnumValues( index, true );
+  }
+  else if ( ! mShared->fieldSupportsEnumValues( index ) )
+  {
+    return;
+  }
+
   //find out type of index
-  QString fieldName = mAttributeFields.at( index ).name();
+  const QString fieldName = mAttributeFields.at( index ).name();
   QString typeName = mAttributeFields.at( index ).typeName();
 
   // Remove schema extension from typeName
   typeName.remove( QRegularExpression( "^([^.]+\\.)+" ) );
 
   //is type an enum?
-  QString typeSql = QStringLiteral( "SELECT typtype FROM pg_type WHERE typname=%1" ).arg( quotedValue( typeName ) );
+  const QString typeSql = QStringLiteral( "SELECT typtype FROM pg_type WHERE typname=%1" ).arg( quotedValue( typeName ) );
   QgsPostgresResult typeRes( connectionRO()->PQexec( typeSql ) );
   if ( typeRes.PQresultStatus() != PGRES_TUPLES_OK || typeRes.PQntuples() < 1 )
   {
+    mShared->setFieldSupportsEnumValues( index, false );
     return;
   }
 
-
-  QString typtype = typeRes.PQgetvalue( 0, 0 );
+  const QString typtype = typeRes.PQgetvalue( 0, 0 );
   if ( typtype.compare( QLatin1String( "e" ), Qt::CaseInsensitive ) == 0 )
   {
     //try to read enum_range of attribute
     if ( !parseEnumRange( enumList, fieldName ) )
     {
-      enumList.clear();
+      mShared->setFieldSupportsEnumValues( index, false );
     }
   }
   else
   {
     //is there a domain check constraint for the attribute?
     if ( !parseDomainCheckConstraint( enumList, fieldName ) )
     {
-      enumList.clear();
+      mShared->setFieldSupportsEnumValues( index, false );
     }
   }
 }
@@ -5166,3 +5174,22 @@ void QgsPostgresSharedData::clear()
   mFeaturesCounted = -1;
   mFidCounter = 0;
 }
+
+bool QgsPostgresSharedData::fieldSupportsEnumValuesIsSet( int index )
+{
+  QMutexLocker locker( &mMutex );
+  return mFieldSupportsEnumValues.contains( index );
+}
+
+bool QgsPostgresSharedData::fieldSupportsEnumValues( int index )
+{
+  QMutexLocker locker( &mMutex );
+  return mFieldSupportsEnumValues.contains( index ) && mFieldSupportsEnumValues[ index ];
+}
+
+void QgsPostgresSharedData::setFieldSupportsEnumValues( int index, bool isSupported )
+{
+  QMutexLocker locker( &mMutex );
+  mFieldSupportsEnumValues[ index ] = isSupported;
+}
+

src/providers/postgres/qgspostgresprovider.h

@@ -522,6 +522,10 @@ class QgsPostgresSharedData
     QVariantList lookupKey( QgsFeatureId featureId );
     void clear();
 
+    bool fieldSupportsEnumValuesIsSet( int index );
+    bool fieldSupportsEnumValues( int index );
+    void setFieldSupportsEnumValues( int index, bool isSupported );
+
   protected:
     QMutex mMutex; //!< Access to all data members is guarded by the mutex
 
@@ -530,6 +534,7 @@ class QgsPostgresSharedData
     QgsFeatureId mFidCounter = 0;                    // next feature id if map is used
     QMap<QVariantList, QgsFeatureId> mKeyToFid;      // map key values to feature id
     QMap<QgsFeatureId, QVariantList> mFidToKey;      // map feature id back to key values
+    QMap<int, bool> mFieldSupportsEnumValues;        // map field index to bool flag supports enum values
 };
 
 // clazy:excludeall=qstring-allocations