Entity Framework Core: How to solve Introducing FOREIGN KEY constraint may cause cycles or multiple cascade paths

Question

I\'m using Entity Framework Core with Code First approach but recieve following error when updating the database:

Introducing FOREIGN KEY constraint \

Answer 1

In your sample code in OnModelCreating you have declared modelBuilder.Entity().HasOne(e => e.User)... twice: at start of method and at end.

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity()       // THIS IS FIRST
        .HasOne(u => u.User).WithMany(u => u.AnEventUsers).IsRequired().OnDelete(DeleteBehavior.Restrict);


    modelBuilder.Entity()
        .HasKey(t => new { t.AnEventId, t.UserId });

    modelBuilder.Entity()
        .HasOne(pt => pt.AnEvent)
        .WithMany(p => p.AnEventUsers)
        .HasForeignKey(pt => pt.AnEventId);

    modelBuilder.Entity()       // THIS IS SECOND.
        .HasOne(eu => eu.User)               // THIS LINES
        .WithMany(e => e.AnEventUsers)       //   SHOULD BE
        .HasForeignKey(eu => eu.UserId);     //   REMOVED

}

Second call overrides first. Remove it.