Why core data is not an ORM

Question

I have read that Core Data is not an ORM? Can anybody please list out the point that why it is not an ORM?

My Point:

1. While using Core Data we work mainly on objects same as in ORM.
2. All the access and manipulation is done on objects.
3. We can change the backend and it support multiple backend like sqlite, plist, in-memory.

Answer 1

Short answer: CoreData is more than ORM implementation.

Long answer:

ORM wikipedia definition is:

Object-relational mapping (ORM, O/RM, and O/R mapping) in computer software is a programming technique for converting data between incompatible type systems in relational databases and object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language.

Put it simply, it's just an abstraction, or virtualization of a relational persistence layer that eases the effort to access and write to/in it. (Note: object-relational mapping)

While CoreData definition states:

Core Data is a framework that you use to manage the model layer objects in your application. It provides generalized and automated solutions to common tasks associated with object life cycle and object graph management, including persistence.

Coredata definition does not mention to stick with ORM definition, eventhough it seems fully compliant.

The difference I found is: since CoreData framework separates its abstraction layer (Managed Objects and Managed object contexts) from its persistence layer (Persistence Store) through its Persistence Store Coordinator, it can abstract objects from a relational-database, as sqlite, aswell as from any other not relational persistence layer.

To support this statement, here NSHipster brief description:

Contrary to popular belief, Core Data is not an Object-Relational Mapper, but rather an object graph and persistence framework, capable of [...]. Using Core Data as an ORM necessarily limits the capabilities of Core Data and muddies its conceptual purity.