Entity Framework Junction(ish) Table Mapping Code FIrst

Question

How does one map a junction table with values in EF v6.2?

Let's say you have entities named "Item1", "Item2" and another entity of them mapped:

public class Item1
{
    [Key]
    public long Id { get; set; }

    public virtual ICollection<MapItem> { get; set; }
}

public class Item2
{
    [Key]
    public int Id { get; set; }

    public virtual ICollection<MapItem> { get; set; }
}

public class MapItem
{
    public long Item1ID {get; set;} //PK, FK
    public int Item2ID {get; set;} //PK, FK

    public decimal Value {get; set;}
    public string Name {get; set;}

    public virtual Item1 {get; set;}
    public virtual Item2 {get; set;}
}

EDMX automatically generates this but how would I build this with code-first / FluentAPI to build an accessible collection of the MapItem entity?

I've tried updating the mapped entity to use [Key(Order = 1)] and [Key(Order = 2)] on the PK & FK values for MapItem .

This seems like a weird scenario considering it's not a true junction table of 2 entities, but also holds value as well.

Answer 1

Here I was able to get it resolved using FluentAPI.

Here I modified the entity class:

public class MapItem
{
    [Key(Order = 1)]
    public long Item1ID {get; set;} //PK, FK

    [Key(Order = 2)]
    public int Item2ID {get; set;} //PK, FK

    public decimal Value {get; set;}
    public string Name {get; set;}

    public virtual Item1 {get; set;}
    public virtual Item2 {get; set;}
}

Then in the relationship builder:

 modelBuilder.Entity<MapItem>().HasKey(q => new
 {
        q.Item1ID, q.Item2ID
 });
​
 modelBuilder.Entity<MapItem>().HasRequired(q => q.Item1).WithMany(q => q.MapItem).HasForeignKey(q => q.Item1ID);
 modelBuilder.Entity<MapItem>().HasRequired(q => q.Item2).WithMany(q => q.MapItem).HasForeignKey(q => q.Item2ID);

The crucial part was the "HasKey" method which correctly mapped the entities.