EF Core中的多對多關系映射

Question

我對EF核心中的多對多關系有疑問。 我有以下模型類：

public class Meal
{
    public int Id { get; set; }
    [Required]
    public int Insulin { get; set; }
    public MealType Type { get; set; }

    public ICollection<MealFood> MealFoods { get; set; }

    public Meal()
    {
        MealFoods = new Collection<MealFood>();
    }
}

public class Food
{
    public int Id { get; set; }
    [StringLength(255)]
    public string Name { get; set; }
    [Required]
    public int Carbohydrates { get; set; }
    public ICollection<MealFood> MealFoods { get; set; }

    public Food()
    {
        MealFoods = new Collection<MealFood>();
    }
}

public class MealFood
{
    public int MealId { get; set; }
    public Meal Meal { get; set; }
    public int FoodId { get; set; }
    public Food Food { get; set; }
}

我有以下API資源類：

public class MealResource
{
    public int Id { get; set; }
    public int Insulin { get; set; }
    public MealType Type { get; set; }

    public ICollection<FoodResource> Foods { get; set; }

    public MealResource()
    {
        Foods = new Collection<FoodResource>();
    }
}

我已經在我的DbContext中完成了映射：

protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<MealFood>().HasKey(mf => new { mf.MealId, mf.FoodId });
        modelBuilder.Entity<MealFood>().HasOne(mf => mf.Meal).WithMany(m => m.MealFoods).HasForeignKey(mf => mf.MealId);
        modelBuilder.Entity<MealFood>().HasOne(mf => mf.Food).WithMany(f => f.MealFoods).HasForeignKey(mf => mf.FoodId);
    }

我對此電話有疑問：

var meals = await context.Meals.Include(m => m.MealFoods).ToListAsync();

這幾乎返回了我需要的所有內容，但MealFoods的導航屬性除外

我之所以需要這些屬性，是因為我想進行以下映射：

CreateMap<Meal, MealResource>().ForMember(mr => mr.Foods, opt => opt.MapFrom(x => x.MealFoods.Select(y => y.Food).ToList()));

我已經發現了這一點： Automapper多對多映射

但是（也許我什么也沒得到）這是行不通的，因為MealFood中名為Food的屬性為null。

我希望我不要解釋得太復雜。

Answer 1

當您包含導航屬性時，EF Core會自動填充逆向導航屬性，例如，包括Meal.MealFoods將自動填充MealFood.Meal ，包括Food.MealFoods將自動填充MealFood.Food等。為了填充其他導航屬性，您需要使用另外的ThenInclude 。 例如

var meals = await context.Meals
    .Include(m => m.MealFoods)
        .ThenInclude(mf => mf.Food) // <--
    .ToListAsync();

要么

var foods = await context.Foods
    .Include(f => f.MealFoods)
        .ThenInclude(mf => mf.Meal) // <--
    .ToListAsync();