From ebc9e029f0fdb4081be563ed7ddaf242a7b551a3 Mon Sep 17 00:00:00 2001
From: Matthias Kuhn <matthias@opengis.ch>
Date: Sun, 29 Nov 2015 17:45:30 +0100
Subject: [PATCH] Relations are only valid if the id is set

---
 src/core/qgsrelation.cpp | 28 ++++++++++++++++++++++++++++
 src/core/qgsrelation.h   |  4 ++++
 2 files changed, 32 insertions(+)

diff --git a/src/core/qgsrelation.cpp b/src/core/qgsrelation.cpp
index b936b98f2cf..2c7c0f56fa2 100644
--- a/src/core/qgsrelation.cpp
+++ b/src/core/qgsrelation.cpp
@@ -111,6 +111,8 @@ void QgsRelation::writeXML( QDomNode &node, QDomDocument &doc ) const
 void QgsRelation::setRelationId( const QString& id )
 {
   mRelationId = id;
+
+  updateRelationStatus();
 }
 
 void QgsRelation::setRelationName( const QString& name )
@@ -260,6 +262,29 @@ QList<QgsRelation::FieldPair> QgsRelation::fieldPairs() const
   return mFieldPairs;
 }
 
+QgsAttributeList QgsRelation::referencedFields() const
+{
+  QgsAttributeList attrs;
+
+  Q_FOREACH ( const FieldPair& pair, mFieldPairs )
+  {
+    attrs << mReferencedLayer->fieldNameIndex( pair.second );
+  }
+  return attrs;
+}
+
+QgsAttributeList QgsRelation::referencingFields() const
+{
+  QgsAttributeList attrs;
+
+  Q_FOREACH ( const FieldPair& pair, mFieldPairs )
+  {
+    attrs << mReferencingLayer->fieldNameIndex( pair.first );
+  }
+  return attrs;
+
+}
+
 bool QgsRelation::isValid() const
 {
   return mValid;
@@ -274,6 +299,9 @@ void QgsRelation::updateRelationStatus()
 
   mValid = true;
 
+  if ( mRelationId.isEmpty() )
+    mValid = false;
+
   if ( !mReferencedLayer || !mReferencingLayer )
   {
     mValid = false;
diff --git a/src/core/qgsrelation.h b/src/core/qgsrelation.h
index 4bd6eb95a16..1feb513fa07 100644
--- a/src/core/qgsrelation.h
+++ b/src/core/qgsrelation.h
@@ -227,6 +227,10 @@ class CORE_EXPORT QgsRelation
      */
     QList< FieldPair > fieldPairs() const;
 
+    QgsAttributeList referencedFields() const;
+
+    QgsAttributeList referencingFields() const;
+
     /**
      * Returns the validity of this relation. Don't use the information if it's not valid.
      *