Code First: Independent associations vs. Foreign key associations?

by

If you want to take full advantage of ORM you will definitely use Entity reference:

public class Order
{
    public int ID { get; set; }
    public Customer Customer { get; set; } // <-- Customer object
    ...
}

Once you generate an entity model from a database with FKs it will always generate entity references. If you don’t want to use them you must manually modify the EDMX file and add properties representing FKs. At least this was the case in Entity Framework v1 where only Independent associations were allowed.

Entity framework v4 offers a new type of association called Foreign key association. The most obvious difference between the independent and the foreign key association is in Order class:

public class Order
{
    public int ID { get; set; }
    public int CustomerId { get; set; }  // <-- Customer ID
    public Customer Customer { get; set; } // <-- Customer object
    ...
}

As you can see you have both FK property and entity reference. There are more differences between two types of associations:

Independent association

  • It is represented as separate object in ObjectStateManager. It has its own EntityState!
  • When building association you always need entitites from both ends of association
  • This association is mapped in the same way as entity.

Foreign key association

  • It is not represented as separate object in ObjectStateManager. Due to that you must follow some special rules.
  • When building association you don’t need both ends of association. It is enough to have child entity and PK of parent entity but PK value must be unique. So when using foreign keys association you must also assign temporary unique IDs to newly generated entities used in relations.
  • This association is not mapped but instead it defines referential constraints.

If you want to use foreign key association you must tick Include foreign key columns in the model in Entity Data Model Wizard.

Edit:

I found that the difference between these two types of associations is not very well known so I wrote a short article covering this with more details and my own opinion about this.

More Related Contents:

  1. Code-first vs Model/Database-first [closed]
  2. Entity Framework 4 / POCO – Where to start? [closed]
  3. Entity Framework loading child collection with sort order
  4. Why is my Entity Framework Code First proxy collection null and why can’t I set it?
  5. Reset Entity-Framework Migrations
  6. No Entity Framework provider found for the ADO.NET provider with invariant name ‘System.Data.SqlClient’
  7. How do I delete multiple rows in Entity Framework (without foreach)
  8. Entity Framework 6 Code first Default value
  9. How to mock the limitations of EntityFramework’s implementation of IQueryable
  10. Batch update/delete EF5
  11. how to update an entity in Entity Framework 4 .NET
  12. Should I enable or disable dynamic proxies with entity framework 4.1 and MVC3?
  13. Asp.Net Web API Error: The ‘ObjectContent`1’ type failed to serialize the response body for content type ‘application/xml; charset=utf-8’
  14. Generate POCO classes in different project to the project with Entity Framework model
  15. Entity Framework: Ignore Columns
  16. mapping private property entity framework code first [duplicate]
  17. MVC3 and Code First Migrations – “model backing the ‘blah’ context has changed since the database was created”
  18. How to create index in Entity Framework 6.2 with fluent configuration
  19. Mocking or faking DbEntityEntry or creating a new DbEntityEntry
  20. Map two different entities to the same table?
  21. EF Code First foreign key without navigation property
  22. Nullable property to entity field, Entity Framework through Code First
  23. LINQ to Entities for subtracting 2 dates
  24. Entity Framework Code First Using Guid as Identity with another Identity Column
  25. AutomaticMigrationsEnabled false or true?
  26. ADO.NET Entity Framework tutorials [closed]
  27. Entity Framework Code First Many to Many Setup For Existing Tables
  28. Compose queries across Entity Data Models
  29. Changing Inherited Types in Entity Framework
  30. Why does the entity framework need an ICollection for lazy loading?

Leave a Comment