From 5e6e75662f2c5959bfe2fc6bbe1760cfbc1fc8bb Mon Sep 17 00:00:00 2001
From: David Signer <david@opengis.ch>
Date: Mon, 16 Dec 2019 17:26:26 +0100
Subject: [PATCH] available values in value relations

---
 .../qgsvaluerelationfieldformatter.sip.in      |  3 +++
 .../qgsvaluerelationfieldformatter.cpp         | 18 ++++++++++++++++++
 .../qgsvaluerelationfieldformatter.h           |  4 +++-
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/python/core/auto_generated/fieldformatter/qgsvaluerelationfieldformatter.sip.in b/python/core/auto_generated/fieldformatter/qgsvaluerelationfieldformatter.sip.in
index e4a5d9e8591..6085b54fe24 100644
--- a/python/core/auto_generated/fieldformatter/qgsvaluerelationfieldformatter.sip.in
+++ b/python/core/auto_generated/fieldformatter/qgsvaluerelationfieldformatter.sip.in
@@ -128,6 +128,9 @@ Returns the (possibly NULL) layer from the widget's ``config`` and ``project``
 .. versionadded:: 3.8
 %End
 
+
+    virtual QList<QVariant> availableValues( const QVariantMap &config, int countLimit ) const;
+
 };
 
 
diff --git a/src/core/fieldformatter/qgsvaluerelationfieldformatter.cpp b/src/core/fieldformatter/qgsvaluerelationfieldformatter.cpp
index eecf9b54de9..4faa20503d7 100644
--- a/src/core/fieldformatter/qgsvaluerelationfieldformatter.cpp
+++ b/src/core/fieldformatter/qgsvaluerelationfieldformatter.cpp
@@ -40,6 +40,11 @@ bool orderByValueLessThan( const QgsValueRelationFieldFormatter::ValueRelationIt
   return qgsVariantLessThan( p1.value, p2.value );
 }
 
+QgsValueRelationFieldFormatter::QgsValueRelationFieldFormatter()
+{
+  setFlags( flags() | QgsFieldFormatter::CanProvideAvailableValues );
+}
+
 QString QgsValueRelationFieldFormatter::id() const
 {
   return QStringLiteral( "ValueRelation" );
@@ -183,6 +188,19 @@ QList<QgsVectorLayerRef> QgsValueRelationFieldFormatter::layerDependencies( cons
   return result;
 }
 
+QList<QVariant> QgsValueRelationFieldFormatter::availableValues( const QVariantMap &config, int countLimit ) const
+{
+  QList<QVariant> values;
+
+  const QgsVectorLayer *referencedLayer = qobject_cast<QgsVectorLayer *>( QgsProject::instance()->mapLayer( config[QStringLiteral( "Layer" )].toString() ) );
+  if ( referencedLayer )
+  {
+    int fieldIndex = referencedLayer->fields().indexOf( config.value( QStringLiteral( "Key" ) ).toString() );
+    values = referencedLayer->uniqueValues( fieldIndex, countLimit ).toList();
+  }
+  return values;
+}
+
 QStringList QgsValueRelationFieldFormatter::valueToStringList( const QVariant &value )
 {
   QStringList checkList;
diff --git a/src/core/fieldformatter/qgsvaluerelationfieldformatter.h b/src/core/fieldformatter/qgsvaluerelationfieldformatter.h
index db799ded4cf..d3454d45c8f 100644
--- a/src/core/fieldformatter/qgsvaluerelationfieldformatter.h
+++ b/src/core/fieldformatter/qgsvaluerelationfieldformatter.h
@@ -56,7 +56,7 @@ class CORE_EXPORT QgsValueRelationFieldFormatter : public QgsFieldFormatter
     /**
      * Constructor for QgsValueRelationFieldFormatter.
      */
-    QgsValueRelationFieldFormatter() = default;
+    QgsValueRelationFieldFormatter();
 
     QString id() const override;
     QString representValue( QgsVectorLayer *layer, int fieldIndex, const QVariantMap &config, const QVariant &cache, const QVariant &value ) const override;
@@ -126,6 +126,8 @@ class CORE_EXPORT QgsValueRelationFieldFormatter : public QgsFieldFormatter
     static QgsVectorLayer *resolveLayer( const QVariantMap &config, const QgsProject *project );
 
     QList<QgsVectorLayerRef> layerDependencies( const QVariantMap &config ) const override SIP_SKIP;
+
+    QList<QVariant> availableValues( const QVariantMap &config, int countLimit ) const override;
 };
 
 Q_DECLARE_METATYPE( QgsValueRelationFieldFormatter::ValueRelationCache )