EF core many to many configuration not working with Fluent API

Question

I am having trouble with understanding and implementing a many to many repationship using the FLuent API and EF Core.

I have looked at this question and set up my relati

Answer 1

You should add the Clients property to the Job class too:

public class Job : IEntityBase
{
   public int Id { get; set; }
   public ICollection<Client> Clients{ get; set; }
}

Then everything should be in order.

Answer 2

For EF Core 5.0 and up, you may (finally) use direct relationships for many-to-many:

modelBuilder
.Entity<Post>()
.HasMany(p => p.Tags)
.WithMany(p => p.Posts)
.UsingEntity(j => j.ToTable("PostTags"));

Source: Relationships - EF Core | Microsoft (many-to-many)

Answer 3

The Fluent API example you are trying to implement comes from EF 6. Many-to-Many relationship configuration is a little different in EF Core. For a start, you need to include an entity to represent the join/bridging table:

public class ClientsJobs
{
    public int ClientId { get; set; }
    public int JobId { get; set; }
    public Client Client { get; set; }
    public Job Job { get; set; }
}

Then you configure it like this in the OnModelCreating method:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<ClientsJobs>()
        .HasKey(x => new { x.ClientId, x.JobId });

    modelBuilder.Entity<ClientsJobs>()
        .HasOne(x => x.Client)
        .WithMany(y => y.Jobs)
        .HasForeignKey(y => y.JobId);

    modelBuilder.Entity<ClientsJobs>()
        .HasOne(x => x.Job)
        .WithMany(y => y.Clients)
        .HasForeignKey(y => y.ClientId);
}

See more about it here: http://www.learnentityframeworkcore.com/configuration/many-to-many-relationship-configuration

Note: you do need to include navigational properties for both ends of the relationship in the related classes, so you need to add a Clients property to your Job entity.