entity-framework , EF: configuring many to many relationship (code first)

EF: configuring many to many relationship (code first)


Tag: entity-framework

In my scenario I have Jobs, Companies and Departments.

Single Job may have only one Company; Company may have multiple Jobs (One-To-Many)

Single Job may have multiple Departments; Department may have multiple Jobs (Many-To-Many).

I want to set relations using Foreign Keys only. For that I have property of Foreign Key and lazy navigation property.

These are my classes:

public class JobEntity
    public int Id

    public Companies CompanyId

    public virtual CompanyEntity Company

    public IList<Departments> Departments

    public virtual IList<DepartmentEntity> DepartmentsNavigation

public class DepartmentEntity
    public Departments Id

    public string Name

    public virtual IList<JobEntity> Jobs

public class CompanyEntity
    public Companies Id

    public string Name

    public virtual List<JobEntity> Jobs

Also, I have many-to-many mapping inside my context:

 protected override void OnModelCreating(DbModelBuilder modelBuilder)

                    .HasMany<DepartmentEntity>(s => s.DepartmentsNavigation)
                    .WithMany(c => c.JobsNavigation)
                    .Map(cs =>


When I set CompanyId into Job, everything work as expected: when I getting Job from DB, I have an associated Company lazy loaded.

However, when I setting into Job list of related foreign keys ('Departments') - when I loading Job from DB this list is null and departments navigation property ('DepartmentsNavigation') having count of 0 (I was expected to have collection of department ids that I set + lazy loaded collection of departments).

What I doing wrong?


For many-to-many, you can't use a foreign key association.

There's a reference to this here:

One-to-one relation in EFv4 always uses Foreign Key association and many-to-many relation always uses Independent association.

and here:

Note: In many-to-many (*:*) you cannot add foreign keys to the entities. In a *:* relationship, the association information is managed with an independent object.

and here:

However, if you have a pure many-to-many relationship that is connected by a join table that contains only foreign keys, the EF will use an independent association to manage such many-to-many relationship.

Your foreign keys are already in the JobsDepartments table, so EF won't let you add additional foreign keys for that relationship in the JobEntity and DepartmentEntity entities.


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