How to make foreign key inside models for particular column of composite primary key in Entity Framework

Question

class1
{
    [key]
    public string id1 {get; set;}

    [Key]
    public string key2 {get; set;}
}

class2
{
    [foreignKey("class1")]
    public string class1Id{ get; set; }
}

Now here inside class2 I want to use only id1 column of class1 as foreign key.

How to do that?

Answer 1

If you prefer data annotations, just apply the ForeignKey attribute on the navigation property and provide a comma separated list with the FK property name

 class1{
    [key]
    public string id1 {get; set;}

    [Key]
    public string key2 {get; set;}
    }

    class2{

    public string id1 { get; set;}

    public string key2 { get; set;}

      [ForeignKey("id1,key2")] // <= the composite FK
      public virtual class1 class1{ get; set; }

    }

using fluent API configuration is much easier to understand and less error prone:

modelBuilder.Entity< class2>()
    .HasRequired(e => e. class1) 
    .HasForeignKey(e => new { e.id1, e.key2 });