EF Core creates multiple foreign key columns

Question

I'm using EF Core with .NET Core 3.1

I have simple example of Client-Event relationship:

public class BaseEntity
{
    [Key]
    [Required]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }
    public DateTime CreatedOn { get; set; }
    public DateTime? ModifiedOn { get; set; }

}

public class Client : BaseEntity
{
    
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public string Phone { get; set; }

}

public class Event : BaseEntity
{

    public DateTime Start { get; set; }
    public DateTime End { get; set; }
    public Client Client { get; set; }
}

In my context, I'm using Fluent API to specify relationships:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
        
    modelBuilder.Entity<Event>()
        .HasOne<Client>()
        .WithMany()
        .IsRequired()
        .OnDelete(DeleteBehavior.Cascade);

}

When I create migration, the client table looks fine, but the event table looks like this:

migrationBuilder.CreateTable(
            name: "Events",
            columns: table => new
            {
                Id = table.Column<int>(nullable: false)
                    .Annotation("SqlServer:Identity", "1, 1"),
                CreatedOn = table.Column<DateTime>(nullable: false),
                ModifiedOn = table.Column<DateTime>(nullable: true),
                Start = table.Column<DateTime>(nullable: false),
                End = table.Column<DateTime>(nullable: false),
                ClientId = table.Column<int>(nullable: false),
                ClientId1 = table.Column<int>(nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_Events", x => x.Id);
                table.ForeignKey(
                    name: "FK_Events_Clients_ClientId",
                    column: x => x.ClientId,
                    principalTable: "Clients",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
                table.ForeignKey(
                    name: "FK_Events_Clients_ClientId1",
                    column: x => x.ClientId1,
                    principalTable: "Clients",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
            });

Finally I end up having two columns: ClientId and ClientId1. Why is Entity Framework creating two columns for my relationship?

I wasn't using Fluent API so far and it worked perfectly with just shadow property ClientId auto-generated, but I needed to configure cascade delete form this entities, and since there is no other way to do it, I specified the relationship as pictured above. Since then, there is additional foreign key column for it.

I tried specifying a foreign key column:

modelBuilder.Entity<Event>()
            .HasOne<Client>()
            .WithMany()
            .IsRequired()
            .HasForeignKey("ClientId")
            .OnDelete(DeleteBehavior.Cascade);

No effect so far. Is there any way to tell EF im using auto generated shadow properties?

Edit #1:

I also tried specyfing Foreign keys properties on my own like this:

public class Event : BaseEntity
{

    public DateTime Start { get; set; }
    public DateTime End { get; set; }
    public int ClientId { get; set; }
    public Client Client { get; set; }
}

and then

modelBuilder.Entity<Event>()
    .HasOne<Client>()
    .WithMany()
    .IsRequired()
    .HasForeignKey(e => e.ClientId)
    .OnDelete(DeleteBehavior.Cascade);

but there is still no effect.

Answer 1

You can try this:

{

    public DateTime Start { get; set; }
    public DateTime End { get; set; }
    public int? ClientId { get; set; }

    [ForeignKey("ClientId ")]
    public virtual Client Client { get; set; }
}

Answer 2

It turns out, relationships can be empty - leaving decision to the framework, but it doesn't really serve Your interest. I modified my code, so there is explicit pointing at the navigation property, and EF recognized the relationship and stopped creating shadow properties for the columns:

modelBuilder.Entity<Event>()
    .HasOne<Client>(e => e.Client)
    .WithMany()
    .IsRequired()
    .OnDelete(DeleteBehavior.Cascade);