Performance: DbDatabaseMappingExtensions.GetEntityTypeMapping was spe…

…nding a sizeable amount of time doing Linq to Objects in this method. A simple rewrite to use simple iterators helps boosting up the performance.

src/EntityFramework/ModelConfiguration/Edm/DbDatabaseMappingExtensions.cs

@@ -98,10 +98,20 @@ public static IEnumerable<StorageEntityTypeMapping> GetEntityTypeMappings(
             DebugCheck.NotNull(databaseMapping);
             DebugCheck.NotNull(entityType);
 
-            return (from esm in databaseMapping.EntityContainerMappings.Single().EntitySetMappings
-                    from etm in esm.EntityTypeMappings
-                    where etm.EntityType == entityType
-                    select etm);
+            // please don't convert this section of code to a Linq expression since
+            // it is performance sensitive, especially for larger models.
+            var mappings = new List<StorageEntityTypeMapping>();
+            foreach (var esm in databaseMapping.EntityContainerMappings.Single().EntitySetMappings)
+            {
+                foreach (var etm in esm.EntityTypeMappings)
+                {
+                    if (etm.EntityType == entityType)
+                    {
+                        mappings.Add(etm);
+                    }
+                }
+            }
+            return mappings;
         }
 
         public static StorageEntityTypeMapping GetEntityTypeMapping(
@@ -110,14 +120,23 @@ public static StorageEntityTypeMapping GetEntityTypeMapping(
             DebugCheck.NotNull(databaseMapping);
             DebugCheck.NotNull(entityType);
 
-            var mappings = (from esm in databaseMapping.EntityContainerMappings.Single().EntitySetMappings
-                            from etm in esm.EntityTypeMappings
-                            where etm.GetClrType() == entityType
-                            select etm);
+            // please don't convert this section of code to a Linq expression since
+            // it is performance sensitive, especially for larger models.
+            var mappings = new List<StorageEntityTypeMapping>();
+            foreach (var esm in databaseMapping.EntityContainerMappings.Single().EntitySetMappings)
+            {
+                foreach (var etm in esm.EntityTypeMappings)
+                {
+                    if (etm.GetClrType() == entityType)
+                    {
+                        mappings.Add(etm);
+                    }
+                }
+            }
 
-            if (mappings.Count() <= 1)
+            if (mappings.Count <= 1)
             {
-                return mappings.SingleOrDefault();
+                return mappings.FirstOrDefault();
             }
 
             // Return the property mapping