Expression builder : add layer_property(...,'distance_units')

To complete the existing function layer_property(...), this change add a new argument 'distance_units' for return a string with the layer distance units (see QgsUnitTypes::DistanceUnit) This function can be used for display units for labels, in layouts or for access to more layer properties in the expression builder for algorithms.
qgis · Apr 6, 2020 · df0f975 · df0f975
1 parent bc1c58b
commit df0f975
Show file tree

Hide file tree

Showing 3 changed files with 5 additions and 1 deletion.
diff --git a/resources/function_help/json/layer_property b/resources/function_help/json/layer_property
@@ -4,7 +4,7 @@
   "description": "Returns a matching layer property or metadata value.",
   "arguments": [
 	{"arg":"layer", "description":"a string, representing either a layer name or layer ID"},
-        {"arg":"property", "description":"a string corresponding to the property to return. Valid options are:<br /><ul><li>name: layer name</li><li>id: layer ID</li><li>title: metadata title string</li><li>abstract: metadata abstract string</li><li>keywords: metadata keywords</li><li>data_url: metadata URL</li><li>attribution: metadata attribution string</li><li>attribution_url: metadata attribution URL</li><li>source: layer source</li><li>min_scale: minimum display scale for layer</li><li>max_scale: maximum display scale for layer</li><li>is_editable: if layer is in edit mode</li><li>crs: layer CRS</li><li>crs_definition: layer CRS full definition</li><li>crs_description: layer CRS description</li><li>extent: layer extent (as a geometry object)</li><li>type: layer type, e.g., Vector or Raster</li><li>storage_type: storage format (vector layers only)</li><li>geometry_type: geometry type, e.g., Point (vector layers only)</li><li>feature_count: approximate feature count for layer (vector layers only)</li><li>path: File path to the layer data source. Only available for file based layers.</li></ul>"}
+        {"arg":"property", "description":"a string corresponding to the property to return. Valid options are:<br /><ul><li>name: layer name</li><li>id: layer ID</li><li>title: metadata title string</li><li>abstract: metadata abstract string</li><li>keywords: metadata keywords</li><li>data_url: metadata URL</li><li>attribution: metadata attribution string</li><li>attribution_url: metadata attribution URL</li><li>source: layer source</li><li>min_scale: minimum display scale for layer</li><li>max_scale: maximum display scale for layer</li><li>is_editable: if layer is in edit mode</li><li>crs: layer CRS</li><li>crs_definition: layer CRS full definition</li><li>crs_description: layer CRS description</li><li>extent: layer extent (as a geometry object)</li><li>distance_units: layer distance units</li><li>type: layer type, e.g., Vector or Raster</li><li>storage_type: storage format (vector layers only)</li><li>geometry_type: geometry type, e.g., Point (vector layers only)</li><li>feature_count: approximate feature count for layer (vector layers only)</li><li>path: File path to the layer data source. Only available for file based layers.</li></ul>"}
   ],
   "examples": [
 	{ "expression":"layer_property('streets','title')", "returns":"'Basemap Streets'"},

diff --git a/src/core/expression/qgsexpressionfunction.cpp b/src/core/expression/qgsexpressionfunction.cpp
@@ -57,6 +57,7 @@
 #include "qgsapplication.h"
 #include "qgis.h"
 #include "qgsexpressioncontextutils.h"
+#include "qgsunittypes.h"
 
 typedef QList<QgsExpressionFunction *> ExpressionFunctionList;
 
@@ -4785,6 +4786,8 @@ static QVariant fcnGetLayerProperty( const QVariantList &values, const QgsExpres
     QVariant result = QVariant::fromValue( extentGeom );
     return result;
   }
+  else if ( QString::compare( layerProperty, QStringLiteral( "distance_units" ), Qt::CaseInsensitive ) == 0 )
+    return QgsUnitTypes::encodeUnit( layer->crs().mapUnits() );
   else if ( QString::compare( layerProperty, QStringLiteral( "type" ), Qt::CaseInsensitive ) == 0 )
   {
     switch ( layer->type() )

diff --git a/tests/src/core/testqgsexpression.cpp b/tests/src/core/testqgsexpression.cpp
@@ -1440,6 +1440,7 @@ class TestQgsExpression: public QObject
       QTest::newRow( "layer_property crs_description" ) << QStringLiteral( "layer_property('%1','crs_description')" ).arg( mPointsLayer->name() ) << false << QVariant( "WGS 84" );
       QTest::newRow( "layer_property crs_definition" ) << QStringLiteral( "layer_property('%1','crs_definition')" ).arg( mPointsLayer->name() ) << false << QVariant( "+proj=longlat +datum=WGS84 +no_defs" );
       QTest::newRow( "layer_property extent" ) << QStringLiteral( "geom_to_wkt(layer_property('%1','extent'))" ).arg( mPointsLayer->name() ) << false << QVariant( "Polygon ((-118.88888889 22.80020704, -83.33333333 22.80020704, -83.33333333 46.87198068, -118.88888889 46.87198068, -118.88888889 22.80020704))" );
+      QTest::newRow( "layer_property distance_units" ) << QStringLiteral( "layer_property('%1','distance_units')" ).arg( mPointsLayer->name() ) << false << QVariant( "degrees" );
       QTest::newRow( "layer_property type" ) << QStringLiteral( "layer_property('%1','type')" ).arg( mPointsLayer->name() ) << false << QVariant( "Vector" );
       QTest::newRow( "layer_property storage_type" ) << QStringLiteral( "layer_property('%1','storage_type')" ).arg( mPointsLayer->name() ) << false << QVariant( "ESRI Shapefile" );
       QTest::newRow( "layer_property geometry_type" ) << QStringLiteral( "layer_property('%1','geometry_type')" ).arg( mPointsLayer->name() ) << false << QVariant( "Point" );