Composite foreign key as primary key

Question

I am currently migrating EF Core 3.0 code-first entity to clean architecture approach.

In EF Core 3.0 this works fine:

namespace SmartCom.Models
{
    public class branch
    {
        [DatabaseGenerated(DatabaseGeneratedOption.None)]
        [MaxLength(128)]
        public virtual string CompanyId { get; set; }

        [MaxLength(128)]
        public string AddressId { get; set; }

        public DateTime CreatedDate { get; set; }

        public int RefNo { get; set; }

        [ForeignKey("AddressId")]
        public address Address { get; set; }
    }
}

At the DB context

protected override void OnModelCreating(ModelBuilder modelBuilder)
{

modelBuilder.Entity<branch>()
  .HasKey(c => new { c.CompanyId, c.BranchId });

With clean architecture, I separated entity business logic from persistence as follows:

1. Business logic model without persistence settings;

namespace SmartComCA.CoSec.Domain.Entities
{
    public class Branch
    {
        public virtual Company Company { get; set; }
        public Address Address { get; set; }
        public DateTime CreatedDate { get; set; }
        public int RefNo { get; set; }
    }
}

2. Persistence configuration in Infrastructure project:

namespace SmartComCA.CoSec.Infrastructure.Persistence.Configuration
{
    public class BranchConfiguration : IEntityTypeConfiguration<Branch>
    {
        public void Configure(EntityTypeBuilder<Branch> builder)
        {
            //builder.HasKey(t => new { t.Company, t.Address});

            builder.HasOne(t => t.Company).WithMany()
                .HasForeignKey("CompanyId");

            builder.HasOne(t => t.Address).WithMany()
                .HasForeignKey("AddressId");

            builder.ToTable("branch");
        }
    }
}

This compiles but fails during add-migration. How do I specify composite foreign key as primary key in clean architecture where persistence is abstracted from business logic?

Answer 1

You can replace the explicit properties with shadow properties . Which you already did indirectly with HasForeignKey fluent API, but following is the explicit definition matching the original definition which also correctly configures the max length for string data types:

builder.Property<string>("CompanyId")
    .IsRequired()
    .HasMaxLength(128);

builder.Property<string>("BranchId")
    .IsRequired()
    .HasMaxLength(128);

Then you can define the composite PK using the shadow property names:

builder.HasKey("CompanyId", "BranchId");

But please note that having shadow PK imposes some limitations/requirements for operations like update and delete, since they would require having the loaded related objects rather than just their keys.