三張表與實體框架之間的關系

Question

我想在三個表之間建立關系。

我的數據庫如下所示： https://ibb.co/VggWGRb

這些是我的課程：

public class Equipment     // model for Equipment table
{
    public int EquipmentID { get; set; }
    public IEnumerable<string> Item { get; set; }
}

public class Car     // model for car table
{
    public int CarID { get; set; }
    public string Brand { get; set; }
    public string Model { get; set; }
    public int Price { get; set; }
    public string Category { get; set; }
    public string Description { get; set; }
    public int Production { get; set; }
    public int Mileage { get; set; }
    public byte[] ImageData { get; set; }
    public string ImageMimeType { get; set; }
}

public class CarEquipment        // model for carequipment table
{
    public int CarID { get; set; }
    public int EquipmentID { get; set; }

    public virtual Car Car { get; set; }
    public virtual ICollection<Equipment> Equipment { get; set; }
}

public class EfDbContext : DbContext
{
    public DbSet<Car> Cars { get; set; }
    public DbSet<Equipment> Equipments { get; set; }
    public DbSet<CarEquipment> CarEquipments { get; set; }
}

我找到了一些解決方案，有人使用context.Guild.Include("Player").ToList();

也許我應該做這樣的事情？

public class EFCarEquipmentRepository : ICarEquipmentRepository
{
    private EfDbContext context = new EfDbContext();

    public IEnumerable<CarEquipment> CarEquipment
    {
        get
        {
            return context.CarEquipments;
        }
    }
}

public interface ICarEquipmentRepository
{
    IEnumerable<CarEquipment> CarEquipment { get; set; }
}

應該如何正確書寫以及如何使用 controller 中的IEnumerable<string> equipment調用汽車 model？

Answer 1

根據問題圖像中顯示的 ER 圖，您可以在 EF 中定義關系，如下所示，

 public class Equipment     // model for Equipment table
{
    public int EquipmentID { get; set; }
    public IEnumerable<string> Item { get; set; }
    public virtual ICollection<CarEquipment> CarEquipments { get; set; }
}

public class Car     // model for car table
{
    public int CarID { get; set; }
    public string Brand { get; set; }
    public string Model { get; set; }
    public int Price { get; set; }
    public string Category { get; set; }
    public string Description { get; set; }
    public int Production { get; set; }
    public int Mileage { get; set; }
    public byte[] ImageData { get; set; }
    public string ImageMimeType { get; set; }
    public virtual ICollection<CarEquipment> CarEquipments { get; set; }
}

public class CarEquipment        // model for carequipmeHnt table
{
    public int CarID { get; set; }
    public int EquipmentID { get; set; }

    public virtual Car Car { get; set; }
    public virtual Equipment Equipment { get; set; }
}

public class EfDbContext : DbContext
{
    public DbSet<Car> Cars { get; set; }
    public DbSet<Equipment> Equipments { get; set; }
    public DbSet<CarEquipment> CarEquipments { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Car>().HasKey(x => x.CarID);
        modelBuilder.Entity<CarEquipment>().HasKey(x => new { x.CarID, x.EquipmentID });
        modelBuilder.Entity<Equipment>().HasKey(x => x.EquipmentID);
        modelBuilder.Entity<CarEquipment>().HasOne(x => x.Equipment).WithMany(x => x.CarEquipments);
        modelBuilder.Entity<CarEquipment>().HasOne(x => x.Car).WithMany(x => x.CarEquipments);
    }
}

現在你可以像這樣訪問 CarEquipment 和 Car，

public class EFCarEquipmentRepository : ICarEquipmentRepository
{
    private EfDbContext context = new EfDbContext();

    public IEnumerable<CarEquipment> CarEquipment
    {
        get
        {
            return context.CarEquipments.Include(x => x.Car);
        }
    }
}

如果你也想訪問設備，只需像這樣鏈接方法，

context.CarEquipments.Include(x => x.Car).Include(x => x.Equipment)

注意：我已經解釋了這一點，保持 EF Core 為參考。 這是可以學習如何在 EF Core 中定義關系的最佳來源之一： MS Doc