Better exception

In cases when some of target schemas does not exist in database or belongs
to another user

Author: alex-kulakov

Orm/Xtensive.Orm.PostgreSql/Sql.Drivers.PostgreSql/v8_0/Extractor.cs

@@ -441,7 +441,12 @@ protected virtual void ExtractSchemaContents(ExtractionContext context)
           && SqlDml.In(relationsTable["relkind"], SqlDml.Row('r', 'v', 'S'));
 
         if (targetSchemes!=null && targetSchemes.Count > 0) {
-          var schemesIndexes = catalog.Schemas.Where(sch => targetSchemes.ContainsKey(sch.Name)).Select(sch => context.ReversedSchemaMap[sch]);
+          var schemesIndexes = catalog.Schemas.Where(sch => targetSchemes.ContainsKey(sch.Name))
+            .Select(sch =>
+              context.ReversedSchemaMap.TryGetValue(sch, out var oid)
+                ? oid
+                : throw new InvalidOperationException(string.Format(Resources.Strings.ExSchemaXDoesNotExistOrBelongsToAnotherUser, sch.Name))
+             );
           select.Where &= SqlDml.In(relationsTable["relnamespace"], CreateOidRow(schemesIndexes));
         }
         select.Columns.Add(relationsTable["oid"], "reloid");