The entity type has multiple properties with the [Key] attribute.
public class NorthwindContext : DbContext
{
public NorthwindContext(DbContextOptions<NorthwindContext> options):base(options) { }
public NorthwindContext() { }
protected override void OnModelCreating(ModelBuilder builder)
{
builder.Entity<Relationship>().HasKey(table => new {
table.FriendId, table.UserId
});
}
public DbSet<Relationship> Relationships { get; set; }
public DbSet<User> Users { get; set; }
}