c# - Entity Framework Core - Multiple one-to-many relationships between two entities

Question

I have two entities - Team and Game. A team can have many games (One-To-Many).

So that would look something like this:

 public class Team
    {
        public int Id { get; set; }
        public string Name { get; set; }

        public ICollection<Game> Games { get; set; }
    }

 public class Game
    {
        public int Id { get; set; }
        public DateTime Date { get; set; }

        public int TeamId { get; set; }
        public Team Team { get; set; }
    }

This works nice, but I want to make it a little more refined by splitting the games into two categories - Home and Away games. This will however introduce another relationship between the two entities and I'm not sure how to define it.

I imagine it will be something like this?

 public class Team
    {
        public int Id { get; set; }
        public string Name { get; set; }

        public ICollection<Game> HomeGames { get; set; }
        public ICollection<Game> AwayGames { get; set; }
    }

public class Game
    {
        public int Id { get; set; }
        public DateTime Date { get; set; }

        public int HomeTeamId { get; set; }
        public Team HomeTeam { get; set; }

        public int AwayTeamId{ get; set; }
        public Team AwayTeam { get; set; }
    }

Doing this confuses Entity Framework and it can't decide how to settle the relationships.

Any ideas?

Answer 1

You have to tell Entity Framework which properties in both entities are involved in one association. In fluent mapping API this is:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Team>().HasMany(t => t.HomeGames)
        .WithOne(g => g.HomeTeam)
        .HasForeignKey(g => g.HomeTeamId);
    modelBuilder.Entity<Team>().HasMany(t => t.AwayGames)
        .WithOne(g => g.AwayTeam)
        .HasForeignKey(g => g.AwayTeamId).OnDelete(DeleteBehavior.Restrict);
}

You have to use the fluent API because by default, EF will try to create two foreign keys with cascaded delete. SQL Server won't allow that because of its infamous "multiple cascade paths" restriction. One of the keys shouldn't be cascading, which can only be configured by the fluent API.