Disabling identity (auto-incrementing) on integer primary key using code first

use attribute :

public class MessageSubject
    {
        [DatabaseGenerated(DatabaseGeneratedOption.None)]
        public int Id { get; set; }
        public string Title { get; set; }
        public string Comment { get; set; }
        public bool BuildIn { get; set; }
    }

Use these data annotation options:

• [System.ComponentModel.DataAnnotations.KeyAttribute()]
• [System.ComponentModel.DataAnnotations.DatabaseGenerated(System.ComponentModel.DataAnnotations.DatabaseGeneratedOption.None)]

You can use FluentMapping:

modelBuilder.Entity<*entityname*>().Property(m => m.*fieldname*)
             .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

If you want to use fluent api with EntityFramework Core 2.0 you write:

modelBuilder.Entity<*myEntity*>()
  .Property(e => e.*myFieldname*)
  .ValueGeneratedNever();