PartialIndexFilterBuilder : add dedicated error for entity refs comparison

Author: alex-kulakov

Orm/Xtensive.Orm/Orm/Building/Builders/PartialIndexFilterBuilder.cs

@@ -88,6 +88,8 @@ protected override Expression VisitBinary(BinaryExpression b)
         return BuildEntityCheck(field, b.NodeType);
       if (entityAccessMap.TryGetValue(right, out field) && IsNull(left))
         return BuildEntityCheck(field, b.NodeType);
+      if (entityAccessMap.TryGetValue(left, out var _) && entityAccessMap.TryGetValue(right, out var _))
+        throw UnableToTranslate(b, Strings.ComparisonOfTwoEntityFieldsIsNotSupported);
 
       return base.VisitBinary(b);
 

Orm/Xtensive.Orm/Strings.Designer.cs

@@ -3473,4 +3473,7 @@ Error: {1}</value>
   <data name="ExXExpressionsWithConstantValuesOfYTypeNotSupported" xml:space="preserve">
     <value>{0} expressions with constant values of {1} type are not supported.</value>
   </data>
+  <data name="ComparisonOfTwoEntityFieldsIsNotSupported" xml:space="preserve">
+    <value>Comparison of two entity fields is not supported.</value>
+  </data>
 </root>