Support for subclassing to define different primary key behavior, and in...

Source/MMRecord/MMRecordRepresentation.h

@@ -196,6 +196,20 @@
  */
 - (NSString *)primaryKeyPropertyName;
 
+/**
+ This method is responsible for determining the name of the primary key property given the entity
+ description for this instance of an MMRecordRepresentation.
+ @param entity The entity description for this representation.
+ @return The name of the primary key property for this entity.
+ @discussion This method is designed to be subclassed if the user wishes to provide a different way
+ of determining which property to use as the primary key for a given type of entity.
+ @warning This method is called once per entity or superentity until a primary key is found, or no
+ further superentity exists for a given entity. It is in this way that this class supports entity
+ inheritance, meaning that if no primary key property is designated on an entity then the class will
+ go through the chain of superentities to see if a primary key exists there.
+ */
+- (NSString *)primaryKeyPropertyNameForEntityDescription:(NSEntityDescription *)entity;
+
 /**
  This method returns the primary key attribute description for this entity. This method will return
  nil if the entity uses a relationship for its primary key.

Source/MMRecord/MMRecordRepresentation.m

@@ -75,7 +75,9 @@ - (instancetype)initWithEntity:(NSEntityDescription *)entity {
         _attributeRepresentations = [NSMutableArray array];
         _relationshipRepresentations = [NSMutableArray array];
         _recordClassDateFormatter = [NSClassFromString([entity managedObjectClassName]) dateFormatter];
-        _primaryKey = [self primaryAttributeKeyForEntityDescription: entity];
+        _primaryKey = [self representationPrimaryKeyForEntityDescription:entity];
+        //TODO: Improve error handling for invalid primary key that may be returned from a subclass
+        //      or be misconfigured in the model file.
 
         [self createRepresentationMapping];
     }
@@ -105,6 +107,25 @@ - (NSString *)primaryKeyPropertyName {
     return self.primaryKey;
 }
 
+- (NSString *)primaryKeyPropertyNameForEntityDescription:(NSEntityDescription *)entity {
+    NSDictionary *userInfo = [entity userInfo];
+    NSString *primaryKeyPropertyName = [userInfo valueForKey:MMRecordEntityPrimaryAttributeKey];
+
+    return primaryKeyPropertyName;
+}
+
+- (NSString *)representationPrimaryKeyForEntityDescription:(NSEntityDescription *)entity {
+    NSString *primaryKeyPropertyName;
+    NSEntityDescription *currentEntity = entity;
+
+    while (!primaryKeyPropertyName && currentEntity) {
+        primaryKeyPropertyName = [self primaryKeyPropertyNameForEntityDescription:entity];
+        currentEntity = currentEntity.superentity;
+    }
+
+    return primaryKeyPropertyName;
+}
+
 - (NSAttributeDescription *)primaryAttributeDescription {
     NSString *primaryKeyPropertyName = [self primaryKeyPropertyName];
     id primaryKeyRepresentation = self.representationDictionary[primaryKeyPropertyName];
@@ -116,19 +137,6 @@ - (NSAttributeDescription *)primaryAttributeDescription {
     return nil;
 }
 
-- (NSString *)primaryAttributeKeyForEntityDescription: (NSEntityDescription *)entity {
-    NSString *primaryKey;
-    NSEntityDescription *currentEntity = entity;
-
-    while (!primaryKey && currentEntity) {
-        NSDictionary *userInfo = [entity userInfo];
-        primaryKey = [userInfo valueForKey:MMRecordEntityPrimaryAttributeKey];
-        currentEntity = currentEntity.superentity;
-    }
-
-    return primaryKey;
-}
-
 - (id)primaryKeyValueFromDictionary:(NSDictionary *)dictionary {
     id primaryKeyRepresentation = self.representationDictionary[self.primaryKey];