EF Core单向自引用实体绑定 [英] EF Core one-way self referencing entity binding

问题描述

我已经使用EF Core建立了一个自我参照实体，如下所示:

I have set up a self referential entity using EF Core which looks like this:

实体

public class DetailType
{
    public int DetailTypeId { get; set; }
    public string Name { get; set; }

    public int? ParentTypeId { get; set; }
    public DetailType ParentType { get; set; }
    public IEnumerable<DetailType> ChildTypes { get; set; }
}

绑定

modelBuilder.Entity<DetailType>()
    .ToTable("detailtype")
    .HasOne(x => x.ParentType)
    .WithMany(x => x.ChildTypes)
    .HasForeignKey(x => x.ParentTypeId);

我正在通过API检索这些实体，当前结果如下所示:

I am retrieving these entities via an API and the current result looks something like this:

[
    {
        "detailTypeId": 20,
        "name": "Money",
        "parentTypeId": null,
        "parentType": null,
        "childTypes": null
    },
    {
        "detailTypeId": 22,
        "name": "Optional Extra",
        "parentTypeId": null,
        "parentType": null,
        "childTypes": [
            {
                "detailTypeId": 42,
                "name": "Extra Nights",
                "parentTypeId": 22,
                "childTypes": null
            }
        ]
    },
    {
        "detailTypeId": 42,
        "name": "Extra Nights",
        "parentTypeId": 22,
        "parentType": {
            "detailTypeId": 22,
            "name": "Optional Extra",
            "parentTypeId": null,
            "parentType": null,
            "childTypes": []
        },
        "childTypes": null
    }
]

我遇到的问题是数组中的第三项与第二项相反.有没有一种方法可以避免这种情况，所以我只有父母->子女关系，而不是父母->子女以及子女->父母.上面的示例是我的API实际上返回的内容的简化版本，因此我想尽可能减少不必要的膨胀，因为会发生很多关系.

The problem I have with this is that the third item in the array is just the reverse of the second. Is there a way to avoid this so that I only have the parent -> child relationship rather than both parent -> child as well as child -> parent. The example above is a heavily cut-down version of what my API is actually returning so I want to reduce the unnecessary bloat as much as possible because there'll be a lot of relationships going on.

理想情况下，我想要的是摆脱ParentType属性，但仍然拥有ChildTypes集合，但是我不确定如何在模型构建器中定义它.

Ideally what I want is to just get rid of the ParentType property but still have the ChildTypes collection but I'm not sure how to define that in the model builder.

我已删除不需要的流畅关系.我还尝试了以下方法:

I have removed the fluent relationship as it's not needed. I've also tried the following:

var roots = this.Items.Where(x => x.ParentTypeId == null);
foreach (var root in roots)
{
    root.ChildTypes = this.Items.Where(x => x.ParentTypeId == root.DetailTypeId);
}

return roots.ToList();

(顺便说一下， this.Items 是DbSet)

(this.Items is the DbSet by the way)

但是，这需要将 ChildTypes 更改为 IQueryable ，当我这样做时，会出现以下异常:

However this requires changing ChildTypes to an IQueryable and when I do that I get the following exception:

实体类型上导航属性'ChildTypes'的类型"DetailType"是"EntityQueryable"，未实现ICollection.集合导航属性必须实现目标类型的ICollection<>.

The type of navigation property 'ChildTypes' on the entity type 'DetailType' is 'EntityQueryable' which does not implement ICollection. Collection navigation properties must implement ICollection<> of the target type.

推荐答案

第一件事-您无需在模型构建器中指定此关系.它可以自行解决.

First things first - you don't need to specify this relation(s) in the model builder. It figures it out on its own.

然后关于您的问题-我想到的第一件事(我不知道您的整个数据集)是获取所有具有 ParentTypeId ==的 DetailType 对象空.

Then regarding your question - the first thing, that comes to my mind (I don't know your entire dataset) is to get all the DetailType objects, that have ParentTypeId == null.

这样，您将获得根，然后递归地构建子元素的 tree .

By this you will get the roots, and then, recursively build the tree of child elements.

这样做将清理您的结果，并且您将看到想要看到的结构.

Doing this will clean-up your result, and you will see the structure as you want to see it.

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