Many to one migrations fails on foreign key long

Question

I have 2 models:

public class Text
{
    public long Id { get; set; }
    public string Text { get; set; }
}

public class User
{
    public int Id { get; set; }
    public ICollection<Text> Texts { get; set; }
}

My model build on user is that

e.HasMany(o => o.Texts).WithOne().HasForeignKey(d => d.Id).IsRequired();

When I try to run:

dotnet ef migrations add

I get this error:

with foreign key properties {'Id' : long} cannot target the primary key {'Id' : int} because it is not compatible. Configure a principal key or a set of compatible foreign key properties for this relationship.

UPDATE:

It should be able for new models to have a collection of the table Texts like:

public class Customer
{
    public int Id { get; set; }
    public ICollection<Text> Texts { get; set; }
}

....

e.HasMany(o => o.Texts).WithOne().HasForeignKey(d => d.Id).IsRequired();

Answer 1

Had similar problem using EF Core but didn't want to include the (equivalent in my class) UserId on the dependent entity Text, just to make happy EF. Finally found that you can replace the primary key used in the relationship (UserId) using HasPrincipalKey()

    modelBuilder.Entity<User>()
        .HasMany(t => t.Texts)
        .WithOne()
        .HasPrincipalKey(u => u.Text);

Answer 2

In the EF context configuration, specifically in the HasForeignKey() you are supposed to specify Which property on the Text model should be the foreign key that points to the User model?

Since User model's primary key is an int, the foreign key pointing from Text to User should naturally also be an int.

I think the mistake you've made is that you are configuring the PK of Textto also be the FK for the relationship Text -> User. Try to change your Text model to :

public class Text
{
   public long Id { get; set; }
   public string Text{ get; set; }
   public int UserId { get; set; }
}

And your configuration to:

e.HasMany(o => o.Texts).WithOne().HasForeignKey(d => d.UserId).IsRequired();

Answer 3

Firstly, change your Model naming please,

public class Text
{
    public long Id { get; set; }
    public int UserId { get; set; }// add a foreign key that could point to User.Id
    public string Body { get; set; }//you cannot have a string property called "Text".
    public virtual User Owner { get; set; }
}
public class User
{
    public int Id { get; set; }
    public virtual ICollection<Text> Texts { get; set; } = new HashSet<Text>();
}

builder.Entity<Text>(table =>
        {
            table.HasKey(x => x.Id);

            table.HasOne(x => x.User)
            .WithMany(x => x.Texts)
            .HasForeignKey(x => x.UserId)
            .HasPrincipalKey(x => x.Id)//<<== here is core code to let foreign key userId point to User.Id.
            .OnDelete(DeleteBehavior.Cascade);
        });

the reason we have to figure out which key is referred is because of multiple primary keys. I saw it once in MSDN, but cannot find it back.

You can use shadow properties for foreign keys, it looks popular now.

public class Text
{
    public long Id { get; set; }
    public string Body { get; set; }
    public virtual User Owner { get; set; }
}
public class User
{
    public int Id { get; set; }
    public virtual ICollection<Text> Texts { get; set; } = new HashSet<Text>();
}

builder.Entity<Text>(table =>
        {
            table.HasKey(x => x.Id);

            // Add the shadow property to the model
            table.Property<int>("UserId");

            table.HasOne(x => x.User)
            .WithMany(x => x.Texts)
            .HasForeignKey("UserId")//<<== Use shadow property
            .HasPrincipalKey(x => x.Id)//<<==point to User.Id.
            .OnDelete(DeleteBehavior.Cascade);
        });