使用Entity Framework插入主实体时依赖实体未入库问题

首先，实体类定义如下：

public class Restaurant : Entity
{
    public string Name { get; set; }
    public int OwnerId { get; set; }
    public virtual Owner Owner { get; set; }
    public virtual Menu Menu { get; set; }

    public Restaurant()
    {
        Menu = new Menu();
    }
}
public class Menu : Entity
{
    public int RestaurantId { get; set; }
    public virtual ICollection<Campaign> Campaigns { get; set; }
    public virtual ICollection<Category> Categories { get; set; }
    public virtual Restaurant Resturant { get; set; }

    public Menu()
    {
        Campaigns = new HashSet<Campaign>();
        Categories = new HashSet<Category>();
    }
}

它们之间为一对一关系，配置如下：

modelBuilder.Entity<Restaurant>(r =>
{
    r.HasOne(r => r.Owner)
    .WithMany()
    .HasForeignKey(r =>r.OwnerId);

    r.HasOne(r => r.Menu)
    .WithOne(m => m.Resturant)
    .HasForeignKey<Menu>(m => m.RestaurantId);
});

modelBuilder.Entity<Menu>(m =>
{
    m.HasMany(m => m.Campaigns)
    .WithOne(c => c.Menu)
    .HasForeignKey(x => x.MenuId);

    m.HasMany(m => m.Categories)
    .WithOne(c => c.Menu)
    .HasForeignKey(c => c.MenuId);

    m.HasOne(m => m.Resturant)
    .WithOne(r => r.Menu);
    
});

处理CreateRestaurantCommand请求创建Restaurant时，代码逻辑如下：

public class CreateRestaurantCommandHandler : IRequestHandler<CreateRestaurantCommand, CreatedRestaurantResponseDto>
{
    private readonly IRestaurantRepository _restaurantRepository;
    private readonly RestaurantBusinessRules _restaurantBusinessRules;

    public CreateRestaurantCommandHandler(IRestaurantRepository restaurantRepository, RestaurantBusinessRules restaurantBusinessRules)
    {
        _restaurantRepository = restaurantRepository;
        _restaurantBusinessRules = restaurantBusinessRules;
    }

    public async Task<CreatedRestaurantResponseDto> Handle(CreateRestaurantCommand request, CancellationToken cancellationToken)
    {
        await _restaurantBusinessRules.DoesOwnerExistAndHaveRestaurantWithSameName(request.OwnerId, request.RestaurantName);

        Restaurant restaurant = new()
        {
            Name = request.RestaurantName,
            OwnerId = request.OwnerId,
        };
        Restaurant createdRestaurant = await _restaurantRepository.CreateAsync(restaurant);

        CreatedRestaurantResponseDto response = new()
        {
            Id = createdRestaurant.Id,
            Name = createdRestaurant.Name,
            OwnerId = createdRestaurant.OwnerId
        };
        return response;

    }
}

Restaurant创建正常，但构造函数中初始化的Menu未插入数据库。CreateAsync方法实现如下：

public async Task<TEntity> CreateAsync(TEntity entity)
{
    Context.Entry(entity).State = EntityState.Added;
    await Context.SaveChangesAsync();
    return entity;
}

尝试过空构造函数初始化Menu、修改DbContext配置，均未解决问题。

1. 替换手动状态设置为Add方法（推荐） #

手动设置EntityState.Added只会标记当前实体，EF Core不会自动处理关联的导航属性。改用Context.Set<TEntity>().Add(entity)，EF会自动遍历实体图，将关联的Menu也标记为Added：

public async Task<TEntity> CreateAsync(TEntity entity)
{
    Context.Set<TEntity>().Add(entity);
    await Context.SaveChangesAsync();
    return entity;
}

2. 修正导航属性拼写错误 #

Menu类中的Resturant拼写错误（应为Restaurant），会导致EF无法正确识别关联关系，修正后同步更新Fluent配置：

// Menu类修正
public virtual Restaurant Restaurant { get; set; }

// Fluent配置修正
modelBuilder.Entity<Restaurant>(r =>
{
    r.HasOne(r => r.Menu)
     .WithOne(m => m.Restaurant) // 同步修正
     .HasForeignKey<Menu>(m => m.RestaurantId);
});

modelBuilder.Entity<Menu>(m =>
{
    m.HasOne(m => m.Restaurant) // 同步修正
     .WithOne(r => r.Menu);
});

3. 手动标记Menu为Added（备选） #

如果必须保留手动设置状态的逻辑，需同时标记Menu并设置外键：

public async Task<TEntity> CreateAsync(TEntity entity)
{
    Context.Entry(entity).State = EntityState.Added;
    if (entity is Restaurant restaurant && restaurant.Menu != null)
    {
        Context.Entry(restaurant.Menu).State = EntityState.Added;
        restaurant.Menu.RestaurantId = restaurant.Id;
    }
    await Context.SaveChangesAsync();
    return entity;
}

内容的提问来源于stack exchange，提问作者ashwor11