如何使用ADO.NET实体框架代码优先创建一对多关系？

Question

I am struggling with an issue and from what I've seen none of the propsed solutions work.

Basically I have two classes:

public class Role
{
    [Key]
    public int ID { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
}

public class ActionType
{
    public int ID { get; set;}
    public string Name { get; set; }
    public string Description { get; set; }
    public virtual ICollection<Role> AllowedRoles { get; set; }

    public ActionType()
    {
        this.AllowedRoles = new List<Role>();
    }  
}

I would like for EF to force an association table in the DB, where the FK is used to reference the one to many relation. Somehow code first creates a table for my Role where a column ActionType_ID is added. Not useful of course when more Role s are added to one ActionType . A DBUpdateExcpetion is being trown.

Any thoughts on how I should resolve this? The point being that classe Role doesn't refer to ActionType, since this is not useful.

Thank you!

Answer 1

What are you really trying to do? At the moment you can add more Role s to single ActionType but single Role cannot be added to multiple ActionType s. Do you want that as well?

In such case you are not doing one-to-many association but many-to-many. Only many-to-many relation uses junction (association) table. One-to-many relation indeed means that dependent entity (the one on many side) has FK to principal entity. The simplest approach is defining navigation property in Role as well:

public class Role
{
    public int ID { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public virtual ICollection<ActionType> ActionTypes { get; set; } 
}

public class ActionType
{
    public int ID { get; set;}
    public string Name { get; set; }
    public string Description { get; set; }
    public virtual ICollection<Role> AllowedRoles { get; set; } 
}

If you don't want to have navigation property in Role you must use fluent API to describe the relation.

public class Context : DbContext
{
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<ActionType>()
                    .HasMany(a => a.AllowedRoles)
                    .WithMany();
    }
}