[FEATURE][expressions] Expanded support for date/time calcs

Adds support for date - date, time - time and datetime - datetime
type calculations which return an interval.

src/core/qgsexpression.cpp

@@ -4051,21 +4051,40 @@ QVariant QgsExpression::NodeBinaryOperator::eval( QgsExpression *parent, const Q
         }
         return QVariant( computeDateTimeFromInterval( dL, &iL ) );
       }
-      else if (( vL.type() == QVariant::Date && vR.type() == QVariant::Time ) ||
-               ( vR.type() == QVariant::Date && vL.type() == QVariant::Time ) )
+      else if ( mOp == boPlus && (( vL.type() == QVariant::Date && vR.type() == QVariant::Time ) ||
+                                  ( vR.type() == QVariant::Date && vL.type() == QVariant::Time ) ) )
       {
         QDate date = getDateValue( vL.type() == QVariant::Date ? vL : vR, parent );
         ENSURE_NO_EVAL_ERROR;
         QTime time = getTimeValue( vR.type() == QVariant::Time ? vR : vL, parent );
         ENSURE_NO_EVAL_ERROR;
-        if ( mOp == boMinus || mOp == boDiv || mOp == boMul || mOp == boMod )
-        {
-          parent->setEvalErrorString( tr( "Can't preform -, /, *, or % on Date and Time" ) );
-          return QVariant();
-        }
         QDateTime dt = QDateTime( date, time );
         return QVariant( dt );
       }
+      else if ( mOp == boMinus && vL.type() == QVariant::Date && vR.type() == QVariant::Date )
+      {
+        QDate date1 = getDateValue( vL, parent );
+        ENSURE_NO_EVAL_ERROR;
+        QDate date2 = getDateValue( vR, parent );
+        ENSURE_NO_EVAL_ERROR;
+        return date1 - date2;
+      }
+      else if ( mOp == boMinus && vL.type() == QVariant::Time && vR.type() == QVariant::Time )
+      {
+        QTime time1 = getTimeValue( vL, parent );
+        ENSURE_NO_EVAL_ERROR;
+        QTime time2 = getTimeValue( vR, parent );
+        ENSURE_NO_EVAL_ERROR;
+        return time1 - time2;
+      }
+      else if ( mOp == boMinus && vL.type() == QVariant::DateTime && vR.type() == QVariant::DateTime )
+      {
+        QDateTime datetime1 = getDateTimeValue( vL, parent );
+        ENSURE_NO_EVAL_ERROR;
+        QDateTime datetime2 = getDateTimeValue( vR, parent );
+        ENSURE_NO_EVAL_ERROR;
+        return datetime1 - datetime2;
+      }
       else
       {
         // general floating point arithmetic

src/core/qgsinterval.cpp

@@ -129,3 +129,15 @@ QDateTime operator+( const QDateTime& start, const QgsInterval& interval )
 {
   return start.addMSecs( static_cast<qint64>( interval.seconds() * 1000.0 ) );
 }
+
+QgsInterval operator-( const QDate& date1, const QDate& date2 )
+{
+  qint64 seconds = date2.daysTo( date1 ) * 24 * 60 * 60;
+  return QgsInterval( seconds );
+}
+
+QgsInterval operator-( const QTime& time1, const QTime& time2 )
+{
+  qint64 mSeconds = time2.msecsTo( time1 );
+  return QgsInterval( mSeconds / 1000.0 );
+}

src/core/qgsinterval.h

@@ -172,13 +172,29 @@ class CORE_EXPORT QgsInterval
 
 Q_DECLARE_METATYPE( QgsInterval )
 
-/** Returns the interval between two datetimes
- * @param dt1 start datetime
- * @param dt2 datetime to subtract, ie subtract dt2 from dt1
+/** Returns the interval between two datetimes.
+ * @param datetime1 start datetime
+ * @param datetime2 datetime to subtract, ie subtract datetime2 from datetime1
  * @note added in QGIS 2.16
  * @note not available in Python bindings
  */
-QgsInterval CORE_EXPORT operator-( const QDateTime& dt1, const QDateTime& dt2 );
+QgsInterval CORE_EXPORT operator-( const QDateTime& datetime1, const QDateTime& datetime2 );
+
+/** Returns the interval between two dates.
+ * @param date1 start date
+ * @param date2 date to subtract, ie subtract date2 from date1
+ * @note added in QGIS 2.16
+ * @note not available in Python bindings
+ */
+QgsInterval CORE_EXPORT operator-( const QDate& date1, const QDate& date2 );
+
+/** Returns the interval between two times.
+ * @param time1 start time
+ * @param time2 time to subtract, ie subtract time2 from time1
+ * @note added in QGIS 2.16
+ * @note not available in Python bindings
+ */
+QgsInterval CORE_EXPORT operator-( const QTime& time1, const QTime& time2 );
 
 /** Adds an interval to a datetime
  * @param start initial datetime

tests/src/core/testqgsexpression.cpp

@@ -834,6 +834,9 @@ class TestQgsExpression: public QObject
       QTest::newRow( "age datetime" ) << "hour(age(to_datetime('2004-03-22 08:30:22'),to_datetime('2004-03-12 07:30:22')))" << false << QVariant( 241.0 );
       QTest::newRow( "date + time" ) << "to_date('2013-03-04') + to_time('13:14:15')" << false << QVariant( QDateTime( QDate( 2013, 3, 4 ), QTime( 13, 14, 15 ) ) );
       QTest::newRow( "time + date" ) << "to_time('13:14:15') + to_date('2013-03-04')" << false << QVariant( QDateTime( QDate( 2013, 3, 4 ), QTime( 13, 14, 15 ) ) );
+      QTest::newRow( "date - date" ) << "to_date('2013-03-04') - to_date('2013-03-01')" << false << QVariant( QgsInterval( 3*24*60*60 ) );
+      QTest::newRow( "datetime - datetime" ) << "to_datetime('2013-03-04 08:30:00') - to_datetime('2013-03-01 05:15:00')" << false << QVariant( QgsInterval( 3*24*60*60 + 3 * 60*60 + 15*60 ) );
+      QTest::newRow( "time - time" ) << "to_time('08:30:00') - to_time('05:15:00')" << false << QVariant( QgsInterval( 3 * 60*60 + 15*60 ) );
 
       // Color functions
       QTest::newRow( "ramp color" ) << "ramp_color('Spectral',0.3)" << false << QVariant( "254,190,116,255" );