包括不与联接实体一起使用 [英] Include not working with join entities

问题描述

例如，我有以下实体（多对多，我也删除了不必要的道具）：

As example I have following entities (many-to-many, I also removed unnessecary props):

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

public class Recipe
{
    public int Id {get; set;}
    public string Name {get; set;}
    public int CategoryId {get; set;}
    public virtual Category Category {get; set;}
}

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

加入实体：

public class BuffetRecipe
{
    public int BuffetId {get; set;}
    public virtual Buffet Buffet {get; set;}
    public int RecipeId {get; set;}
    public virtual Recipe Recipe {get; set;}
}

我想获取属于特定自助餐的所有食谱，

I want to get all recipes that belong to a specific buffet and want include the recipe category.

public IList<Recipe> GetRecipes(int buffetId)
{
    return _dbContext.BuffetRecipes
    .Where(item => item.BuffetId == buffetId)
    .Include(item => item.Recipe)
    .ThenInclude(item => item.Category)
    .Select(item => item.Recipe)
    .ToList();
}

我得到的列表总是返回prop Category = null的食谱。
我没有找到使Include（）与Select（）一起使用的解决方案...

The list I get always returns Recipes with prop Category = null. I didn't find a solution to make the Include() work together with the Select()...

我在做什么错？？

更新：

我可以通过这种方式使它工作……但是我的感觉说这不是一个好方法方式是因为我有2个ToList（）调用...但是现在我的结果中包含类别：

I can make it work this way... but my feeling says this is not a good way because i have 2 ToList() calls... but now I have category included in my results:

public IList<Recipe> GetRecipes(int buffetId)
{
    return _dbContext.BuffetRecipes
    .Where(item => item.BuffetId == buffetId)
    .Include(item => item.Recipe)
    .ThenInclude(item => item.Category)
    .ToList()
    .Select(item => item.Recipe)
    .ToList();
}

推荐答案

包含仅在可以应用于查询的最终结果时才有效。

Include is only effective if it can be applied to the end result of the query.

您可以对其进行更改进入...

You could change it into ...

return _dbContext.BuffetRecipes
    .Where(item => item.BuffetId == buffetId)
    .Select(item => item.Recipe)
    .Include(rcp => rcp.Category)
    .ToList()

...但是，这样做的缺点是您复制食谱 s（与有 BuffetRecipes ）。最好使用食谱开始查询：

... but the drawback of this is that you duplicate your Recipes (as many as they have BuffetRecipes). It's better to start the query with Recipe:

return _dbContext.Recipes
    .Where(rcp => rcp.BuffetRecipes.Any(br => br.BuffetId == buffetId))
    .Include(rcp => rcp.Category)
    .ToList();

您看到我随意添加了导航属性 Recipe.BuffetRecipes 。这对您的模型来说应该没什么问题（相反，我会说）。

You see that I took the liberty to add a navigation property Recipe.BuffetRecipes. This shouldn't be any problem with your model (on the contrary, I'd say).

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