Public default constructor and comparison operator for QgsExpression

doc/api_break.dox

@@ -531,6 +531,7 @@ version instead.</li>
 <li>QgsExpression::Interval has been removed. Use QgsInterval instead.</li>
 <li>replaceExpressionText() no longer accepts a substitution map parameter. Use expression context variables instead.</li>
 <li>helptext() has been renamed to helpText()</li>
+<li>isValid() has been renamed to checkExpression()</li>
 </ul>
 
 \subsection qgis_api_break_3_0_QgsFeature QgsFeature

python/core/qgsexpression.sip

@@ -14,6 +14,14 @@ class QgsExpression
     QgsExpression( const QString& expr );
     ~QgsExpression();
 
+    /**
+     * Checks if this expression is valid.
+     * A valid expression could be parsed but does not necessarily evaluate properly.
+     *
+     * @note Added in QGIS 3.0
+     */
+    bool isValid() const;
+
     //! Returns true if an error occurred when parsing the input expression
     bool hasParserError() const;
     //! Returns parser error
@@ -73,9 +81,9 @@ class QgsExpression
      * @param context optional expression context
      * @param errorMessage will be filled with any error message from the validation
      * @returns true if string is a valid expression
-     * @note added in QGIS 2.12
+     * @note added in QGIS 3.0
      */
-    static bool isValid( const QString& text, const QgsExpressionContext* context, QString &errorMessage );
+    static bool checkExpression( const QString& text, const QgsExpressionContext* context, QString &errorMessage );
 
     //! Return the original, unmodified expression string.
     //! If there was none supplied because it was constructed by sole

src/core/qgsexpression.cpp

@@ -3494,14 +3494,22 @@ const QList<QgsExpression::Function*>& QgsExpression::Functions()
   return gmFunctions;
 }
 
-bool QgsExpression::isValid( const QString &text, const QgsExpressionContext *context, QString &errorMessage )
+bool QgsExpression::checkExpression( const QString &text, const QgsExpressionContext *context, QString &errorMessage )
 {
   QgsExpression exp( text );
   exp.prepare( context );
   errorMessage = exp.parserErrorString();
   return !exp.hasParserError();
 }
 
+void QgsExpression::setExpression( const QString& expression )
+{
+  detach();
+  d->mRootNode = ::parseExpression( expression, d->mParserErrorString );
+  d->mEvalErrorString = QString();
+  d->mExp = expression;
+}
+
 QString QgsExpression::expression() const
 {
   if ( !d->mExp.isNull() )
@@ -3611,6 +3619,18 @@ QgsExpression::~QgsExpression()
     delete d;
 }
 
+bool QgsExpression::operator==( const QgsExpression& other ) const
+{
+  if ( d == other.d || d->mExp == other.d->mExp )
+    return true;
+  return false;
+}
+
+bool QgsExpression::isValid() const
+{
+  return d->mRootNode;
+}
+
 bool QgsExpression::hasParserError() const { return !d->mParserErrorString.isNull(); }
 
 QString QgsExpression::parserErrorString() const { return d->mParserErrorString; }
@@ -3740,7 +3760,7 @@ void QgsExpression::setEvalErrorString( const QString& str )
 QString QgsExpression::dump() const
 {
   if ( !d->mRootNode )
-    return tr( "(no root)" );
+    return QString();
 
   return d->mRootNode->dump();
 }

src/core/qgsexpression.h

@@ -112,7 +112,7 @@ class CORE_EXPORT QgsExpression
     /**
      * Creates a new expression based on the provided string.
      * The string will immediately be parsed. For optimization
-     * {@link prepare()} should alwys be called before every
+     * {@link prepare()} should always be called before every
      * loop in which this expression is used.
      */
     QgsExpression( const QString& expr );
@@ -129,8 +129,30 @@ class CORE_EXPORT QgsExpression
      * it does not need to be re-parsed.
      */
     QgsExpression& operator=( const QgsExpression& other );
+
+    /**
+     * Create an empty expression
+     */
+    QgsExpression();
+
     ~QgsExpression();
 
+    /**
+     * Compares two expressions. The operator returns true
+     * if the expression string is equal.
+     *
+     * @note Added in QGIS 3.0
+     */
+    bool operator==( const QgsExpression& other ) const;
+
+    /**
+     * Checks if this expression is valid.
+     * A valid expression could be parsed but does not necessarily evaluate properly.
+     *
+     * @note Added in QGIS 3.0
+     */
+    bool isValid() const;
+
     //! Returns true if an error occurred when parsing the input expression
     bool hasParserError() const;
     //! Returns parser error
@@ -194,7 +216,14 @@ class CORE_EXPORT QgsExpression
      * @returns true if string is a valid expression
      * @note added in QGIS 2.12
      */
-    static bool isValid( const QString& text, const QgsExpressionContext* context, QString &errorMessage );
+    static bool checkExpression( const QString& text, const QgsExpressionContext* context, QString &errorMessage );
+
+    /**
+     * Set the expression string, will reset the whole internal structure.
+     *
+     * @note Added in QGIS 3.0
+     */
+    void setExpression( const QString& expression );
 
     //! Return the original, unmodified expression string.
     //! If there was none supplied because it was constructed by sole
@@ -1238,11 +1267,6 @@ class CORE_EXPORT QgsExpression
     static QString formatPreviewString( const QVariant& value );
 
   protected:
-    /**
-     * Used by QgsOgcUtils to create an empty
-     */
-    QgsExpression();
-
     void initGeomCalculator();
 
     static QMap<QString, QVariant> gmSpecialColumns;

src/gui/qgsexpressionlineedit.cpp

@@ -129,7 +129,7 @@ QString QgsExpressionLineEdit::expression() const
 bool QgsExpressionLineEdit::isValidExpression( QString *expressionError ) const
 {
   QString temp;
-  return QgsExpression::isValid( expression(), &mExpressionContext, expressionError ? *expressionError : temp );
+  return QgsExpression::checkExpression( expression(), &mExpressionContext, expressionError ? *expressionError : temp );
 }
 
 void QgsExpressionLineEdit::registerExpressionContextGenerator( const QgsExpressionContextGenerator* generator )

src/gui/qgsfieldexpressionwidget.cpp

@@ -113,7 +113,7 @@ QString QgsFieldExpressionWidget::asExpression() const
 bool QgsFieldExpressionWidget::isValidExpression( QString *expressionError ) const
 {
   QString temp;
-  return QgsExpression::isValid( currentText(), &mExpressionContext, expressionError ? *expressionError : temp );
+  return QgsExpression::checkExpression( currentText(), &mExpressionContext, expressionError ? *expressionError : temp );
 }
 
 bool QgsFieldExpressionWidget::isExpression() const

tests/src/python/test_qgsexpression.py

@@ -187,5 +187,13 @@ def testComment(self):
             result = exp.evaluate()
             self.assertEqual(exp_res, result)
 
+    def testValid(self):
+        e = QgsExpression()
+        self.assertFalse(e.isValid())
+        e.setExpression('asdf||#@¼')
+        self.assertFalse(e.isValid())
+        e.setExpression('1')
+        self.assertTrue(e.isValid())
+
 if __name__ == "__main__":
     unittest.main()