title: Prevent Entity Framework from adding duplicated keys in migration with table per type inheritance
body: <p>I have a simple model using table per type inheritance for some entities. The problem is that when I generate the migration using Add-Migration, It creates a duplicated index on the child class' primary key.</p>
  
  <p>Class definitions:</p>
  
  <pre><code>class Product
  {
      [Key]
      public int ProductId { get; set; }
      public int Value { get; set; }
  }
  class Service : Product
  {
      public int OtherValue { get; set; }
  }
  </code></pre>
  
  <p>And in my context, I specify the table names for both classes</p>
  
  <pre><code>class ProductContext : DbContext
  {
      virtual public DbSet&lt;Product&gt; ProductSet { get; set; }
      virtual public DbSet&lt;Service&gt; ServiceSet { get; set; }
      protected override void OnModelCreating(DbModelBuilder modelBuilder)
      {
          modelBuilder.Entity&lt;Product&gt;().ToTable("Product");
          modelBuilder.Entity&lt;Service&gt;().ToTable("Service");
      }
  }
  </code></pre>
  
  <p>Running Add-Migration results in the following:</p>
  
  <pre><code>public override void Up()
  {
      CreateTable(
          "dbo.Product",
          c =&gt; new
              {
                  ProductId = c.Int(nullable: false, identity: true),
                  Value = c.Int(nullable: false),
              })
          .PrimaryKey(t =&gt; t.ProductId);
  
      CreateTable(
          "dbo.Service",
          c =&gt; new
              {
                  ProductId = c.Int(nullable: false),
                  OtherValue = c.Int(nullable: false),
              })
          .PrimaryKey(t =&gt; t.ProductId)
          .ForeignKey("dbo.Product", t =&gt; t.ProductId)
          .Index(t =&gt; t.ProductId);
  
  }
  </code></pre>
  
  <p>It creates an additional index on Service.ProductId when it's already the primary key. Is there some annotation I am missing in order to prevent the index from being added?</p>
  
  <p>Tested with both EF5 and EF6 with the same results.</p>