C#•11mo ago

Entity Framework Core - how to setup this navigation correctly?

Hi all. Very new to Entity Framework Core. I have three classes right now that I want to be database tables. In my Leaderboard class, I have an ICollection called Scores which is meant to hold a list of all LeaderboardScores that link to that Leaderboard. Though, I am unsure how to get it to actually link so the LeaderboardScores that reference that Leaderboard populate that navigation list? My classes are below. I combined them into this one file for ease of sharing, they obviously aren't all in one file in Visual Studio: https://gdl.space/qoxeretoha.cs

15 Replies

Pobiega•11mo ago

convention is for the entity PKey to be called Id in its own class so PlayerId should just be Id inside the Player class, but remain as is when referenced as a foreign key (in LeaderboardScore) other than that, this seems mostly okay. are you getting any errors when generating migrations for this?

KindredOP•11mo ago

That makes sense. I'll change it to be like that

Pobiega•11mo ago

also, personal preference, but I really dislike using attributes to configure my models I much prefer using IEntityTypeConfiguration classes 🙂

KindredOP•11mo ago

I'm not getting errors, but this line doesn't seem like it is working correctly. It should be a many-to-one relationship. So a LeaderboardScore can be connected to one Leaderboard. But a Leaderboard can have many LeaderboardScores as part of it. But EFC doesn't seem to know to populate this line with LeaderboardScore's that use that Leaderboard

KindredOP•11mo ago

Ill look into that! Thankyou

Pobiega•11mo ago

hm...

    public Leaderboard? Leaderboard { get; set; }

    public Player? Player { get; set; }

    public Leaderboard? Leaderboard { get; set; }

    public Player? Player { get; set; }

why are these nullable? surely a score entry cant exist without both these

KindredOP•11mo ago

Yeah a score entry can't exist without them. They are only nullable because Visual Studio gives me a warning if they aren't

Pobiega•11mo ago

Ah, well instead of marking them as nullable to hide the warning, I suggest you fix your models in this case by making the fields required

public required Leaderboard Leaderboard { get; set; }

public required Player Player { get; set; }

public required Leaderboard Leaderboard { get; set; }

public required Player Player { get; set; }

the nullability modifier actually makes EF think they are nullable

namespace EFTestApp.Data.Entities;

public class Leaderboard
{
    public int Id { get; set; }

    public required string Name { get; set; }

    public LeaderboardAccess Access { get; set; } = LeaderboardAccess.PRIVATE;

    public ICollection<LeaderboardScore> Scores { get; set; } = new List<LeaderboardScore>();

    public enum LeaderboardAccess
    {
        PRIVATE,
        PUBLIC
    }
}

public class Player
{
    public int Id { get; set; }
    public required string Name { get; set; }

    public required string UniqueIdentifier { get; set; }

    public Leaderboard Leaderboard { get; set; }
}

public class LeaderboardScore
{
    public int LeaderboardId { get; set; }

    public int PlayerId { get; set; }

    public required Leaderboard Leaderboard { get; set; }

    public required Player Player { get; set; }

    public required int Score { get; set; }
}

namespace EFTestApp.Data.Entities;

public class Leaderboard
{
    public int Id { get; set; }

    public required string Name { get; set; }

    public LeaderboardAccess Access { get; set; } = LeaderboardAccess.PRIVATE;

    public ICollection<LeaderboardScore> Scores { get; set; } = new List<LeaderboardScore>();

    public enum LeaderboardAccess
    {
        PRIVATE,
        PUBLIC
    }
}

public class Player
{
    public int Id { get; set; }
    public required string Name { get; set; }

    public required string UniqueIdentifier { get; set; }

    public Leaderboard Leaderboard { get; set; }
}

public class LeaderboardScore
{
    public int LeaderboardId { get; set; }

    public int PlayerId { get; set; }

    public required Leaderboard Leaderboard { get; set; }

    public required Player Player { get; set; }

    public required int Score { get; set; }
}

KindredOP•11mo ago

Ahh thankyou, I didn't realize that was a keyword

Pobiega•11mo ago

using EFTestApp.Data.Entities;

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;

namespace EFTestApp.Data.Configurations;

public sealed class LeaderboardConfiguration :
    IEntityTypeConfiguration<Player>,
    IEntityTypeConfiguration<LeaderboardScore>,
    IEntityTypeConfiguration<Leaderboard>
{
    public void Configure(EntityTypeBuilder<Player> builder)
    {
        builder
            .Property(x => x.Name)
            .HasMaxLength(100)
            .IsRequired();
    }

    public void Configure(EntityTypeBuilder<LeaderboardScore> builder)
    {
        builder
            .HasKey(x => new { x.PlayerId, x.LeaderboardId });
    }

    public void Configure(EntityTypeBuilder<Leaderboard> builder)
    {
        builder
            .Property(x => x.Name)
            .HasMaxLength(100)
            .IsRequired();
    }
}

using EFTestApp.Data.Entities;

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;

namespace EFTestApp.Data.Configurations;

public sealed class LeaderboardConfiguration :
    IEntityTypeConfiguration<Player>,
    IEntityTypeConfiguration<LeaderboardScore>,
    IEntityTypeConfiguration<Leaderboard>
{
    public void Configure(EntityTypeBuilder<Player> builder)
    {
        builder
            .Property(x => x.Name)
            .HasMaxLength(100)
            .IsRequired();
    }

    public void Configure(EntityTypeBuilder<LeaderboardScore> builder)
    {
        builder
            .HasKey(x => new { x.PlayerId, x.LeaderboardId });
    }

    public void Configure(EntityTypeBuilder<Leaderboard> builder)
    {
        builder
            .Property(x => x.Name)
            .HasMaxLength(100)
            .IsRequired();
    }
}

with these models and these configurations, it seems to work fine the migration generates as expected and looks fine

KindredOP•11mo ago

Thankyou! I'll try this out

Pobiega•11mo ago

hm I found an inconsistancy thou I'd expect a Player to have a Scores property of some sort they are currently linked to a single leaderboard can a player not be part of several leaderboards?

KindredOP•11mo ago

Yeah, so right now a player is unique to a leaderboard. That is purposeful right now

Pobiega•11mo ago

var leaderboard = new Leaderboard() { Name = "Testboard 1", };

var p1 = new Player()
{
    Name = "Steve", UniqueIdentifier = Guid.NewGuid().ToString(), Leaderboard = leaderboard
};
p1.Scores.Add(new LeaderboardScore(leaderboard, p1, 20));

var p2 = new Player()
{
    Name = "John", UniqueIdentifier = Guid.NewGuid().ToString(), Leaderboard = leaderboard
};
p2.Scores.Add(new LeaderboardScore(leaderboard, p2, 50));

_db.Add(leaderboard);
_db.Add(p1);
_db.Add(p2);
await _db.SaveChangesAsync();

var leaderboard = new Leaderboard() { Name = "Testboard 1", };

var p1 = new Player()
{
    Name = "Steve", UniqueIdentifier = Guid.NewGuid().ToString(), Leaderboard = leaderboard
};
p1.Scores.Add(new LeaderboardScore(leaderboard, p1, 20));

var p2 = new Player()
{
    Name = "John", UniqueIdentifier = Guid.NewGuid().ToString(), Leaderboard = leaderboard
};
p2.Scores.Add(new LeaderboardScore(leaderboard, p2, 50));

_db.Add(leaderboard);
_db.Add(p1);
_db.Add(p2);
await _db.SaveChangesAsync();

looks good to me when

Gaming

Programming

Entity Framework Core - how to setup this navigation correctly?