Add a method for getting a quoted string value for use as a literal

in expressions

Author: nyalldawson

python/core/qgsexpression.sip

@@ -340,11 +340,37 @@ class QgsExpression
      */
     static QList<QgsExpression::Function *> specialColumns();
 
-    //! return quoted column reference (in double quotes)
+    /** Returns a quoted column reference (in double quotes)
+     * @see quotedString()
+     * @see quotedValue()
+     */
     static QString quotedColumnRef( QString name );
-    //! return quoted string (in single quotes)
+
+    /** Returns a quoted version of a string (in single quotes)
+     * @see quotedValue()
+     * @see quotedColumnRef()
+     */
     static QString quotedString( QString text );
 
+    /** Returns a string representation of a literal value, including appropriate
+     * quotations where required.
+     * @param value value to convert to a string representation
+     * @note added in QGIS 2.14
+     * @see quotedString()
+     * @see quotedColumnRef()
+     */
+    static QString quotedValue( const QVariant& value );
+
+    /** Returns a string representation of a literal value, including appropriate
+     * quotations where required.
+     * @param value value to convert to a string representation
+     * @param type value type
+     * @note added in QGIS 2.14
+     * @see quotedString()
+     * @see quotedColumnRef()
+     */
+    static QString quotedValue( const QVariant& value, QVariant::Type type );
+
     //////
 
     enum NodeType

src/core/qgsexpression.cpp

@@ -2623,6 +2623,33 @@ QString QgsExpression::quotedString( QString text )
   return QString( "'%1'" ).arg( text );
 }
 
+QString QgsExpression::quotedValue( const QVariant &value )
+{
+  return quotedValue( value, value.type() );
+}
+
+QString QgsExpression::quotedValue( const QVariant& value, QVariant::Type type )
+{
+  if ( value.isNull() )
+    return "NULL";
+
+  switch ( type )
+  {
+    case QVariant::Int:
+    case QVariant::LongLong:
+    case QVariant::Double:
+      return value.toString();
+
+    case QVariant::Bool:
+      return value.toBool() ? "TRUE" : "FALSE";
+
+    default:
+    case QVariant::String:
+      return quotedString( value.toString() );
+  }
+
+}
+
 bool QgsExpression::isFunctionName( const QString &name )
 {
   return functionIndex( name ) != -1;

src/core/qgsexpression.h

@@ -543,11 +543,37 @@ class CORE_EXPORT QgsExpression
      */
     static QList<Function*> specialColumns();
 
-    //! return quoted column reference (in double quotes)
+    /** Returns a quoted column reference (in double quotes)
+     * @see quotedString()
+     * @see quotedValue()
+     */
     static QString quotedColumnRef( QString name );
-    //! return quoted string (in single quotes)
+
+    /** Returns a quoted version of a string (in single quotes)
+     * @see quotedValue()
+     * @see quotedColumnRef()
+     */
     static QString quotedString( QString text );
 
+    /** Returns a string representation of a literal value, including appropriate
+     * quotations where required.
+     * @param value value to convert to a string representation
+     * @note added in QGIS 2.14
+     * @see quotedString()
+     * @see quotedColumnRef()
+     */
+    static QString quotedValue( const QVariant& value );
+
+    /** Returns a string representation of a literal value, including appropriate
+     * quotations where required.
+     * @param value value to convert to a string representation
+     * @param type value type
+     * @note added in QGIS 2.14
+     * @see quotedString()
+     * @see quotedColumnRef()
+     */
+    static QString quotedValue( const QVariant& value, QVariant::Type type );
+
     //////
 
     class Visitor; // visitor interface is defined below

tests/src/core/testqgsexpression.cpp

@@ -1556,6 +1556,20 @@ class TestQgsExpression: public QObject
       QCOMPARE( QgsExpression::quotedString( "hello\\world" ), QString( "'hello\\\\world'" ) );
     }
 
+    void quoted_value()
+    {
+      QCOMPARE( QgsExpression::quotedValue( QVariant( "a string" ) ), QString( "'a string'" ) );
+      QCOMPARE( QgsExpression::quotedValue( QVariant( "a\nstring" ) ), QString( "'a\\nstring'" ) );
+      QCOMPARE( QgsExpression::quotedValue( QVariant( 5 ) ), QString( "5" ) );
+      QCOMPARE( QgsExpression::quotedValue( QVariant( 5 ), QVariant::String ), QString( "'5'" ) );
+      QCOMPARE( QgsExpression::quotedValue( QVariant( 5LL ) ), QString( "5" ) );
+      QCOMPARE( QgsExpression::quotedValue( QVariant( 5.5 ) ), QString( "5.5" ) );
+      QCOMPARE( QgsExpression::quotedValue( QVariant( true ) ), QString( "TRUE" ) );
+      QCOMPARE( QgsExpression::quotedValue( QVariant( true ), QVariant::String ), QString( "'true'" ) );
+      QCOMPARE( QgsExpression::quotedValue( QVariant() ), QString( "NULL" ) );
+      QCOMPARE( QgsExpression::quotedValue( QVariant(), QVariant::String ), QString( "NULL" ) );
+    }
+
     void reentrant()
     {
       // this simply should not crash