Add method to retrieve variables from a QgsExpressionContext as a QVariantMap

Author: nyalldawson

python/core/qgsexpressioncontext.sip

@@ -247,6 +247,13 @@ class QgsExpressionContext
      */
     QVariant variable( const QString& name ) const;
 
+    /**
+     * Returns a map of variable name to value representing all the expression variables
+     * contained by the context.
+     * @note added in QGIS 3.0
+     */
+    QVariantMap variablesToMap() const;
+
     /** Returns true if the specified variable name is intended to be highlighted to the
      * user. This is used by the expression builder to more prominently display the
      * variable.

src/core/qgsexpressioncontext.cpp

@@ -274,6 +274,17 @@ QVariant QgsExpressionContext::variable( const QString& name ) const
   return scope ? scope->variable( name ) : QVariant();
 }
 
+QVariantMap QgsExpressionContext::variablesToMap() const
+{
+  QStringList names = variableNames();
+  QVariantMap m;
+  Q_FOREACH ( const QString& name, names )
+  {
+    m.insert( name, variable( name ) );
+  }
+  return m;
+}
+
 bool QgsExpressionContext::isHighlightedVariable( const QString &name ) const
 {
   return mHighlightedVariables.contains( name );

src/core/qgsexpressioncontext.h

@@ -303,6 +303,13 @@ class CORE_EXPORT QgsExpressionContext
      */
     QVariant variable( const QString& name ) const;
 
+    /**
+     * Returns a map of variable name to value representing all the expression variables
+     * contained by the context.
+     * @note added in QGIS 3.0
+     */
+    QVariantMap variablesToMap() const;
+
     /** Returns true if the specified variable name is intended to be highlighted to the
      * user. This is used by the expression builder to more prominently display the
      * variable.

tests/src/core/testqgsexpressioncontext.cpp

@@ -51,6 +51,8 @@ class TestQgsExpressionContext : public QObject
 
     void cache();
 
+    void valuesAsMap();
+
   private:
 
     class GetTestValueFunction : public QgsScopedExpressionFunction
@@ -688,5 +690,35 @@ void TestQgsExpressionContext::cache()
   QVERIFY( !c.cachedValue( "test" ).isValid() );
 }
 
+void TestQgsExpressionContext::valuesAsMap()
+{
+  QgsExpressionContext context;
+
+  //test retrieving from empty context
+  QVERIFY( context.variablesToMap().isEmpty() );
+
+  //add a scope to the context
+  QgsExpressionContextScope* s1 = new QgsExpressionContextScope();
+  s1->setVariable( "v1", "t1" );
+  s1->setVariable( "v2", "t2" );
+  context << s1;
+
+  QVariantMap m = context.variablesToMap();
+  QCOMPARE( m.size(), 2 );
+  QCOMPARE( m.value( "v1" ).toString(), QString( "t1" ) );
+  QCOMPARE( m.value( "v2" ).toString(), QString( "t2" ) );
+
+  QgsExpressionContextScope* s2 = new QgsExpressionContextScope();
+  s2->setVariable( "v2", "t2a" );
+  s2->setVariable( "v3", "t3" );
+  context << s2;
+
+  m = context.variablesToMap();
+  QCOMPARE( m.size(), 3 );
+  QCOMPARE( m.value( "v1" ).toString(), QString( "t1" ) );
+  QCOMPARE( m.value( "v2" ).toString(), QString( "t2a" ) );
+  QCOMPARE( m.value( "v3" ).toString(), QString( "t3" ) );
+}
+
 QGSTEST_MAIN( TestQgsExpressionContext )
 #include "testqgsexpressioncontext.moc"