c# - 条件 IQueryable 选择 (MVC .NET EF)

Question

我试图在加载一些数据时选择多个子项，但我想在包含项周围放置条件语句。

目前，我有许多不同的选择以不同的方法处理 1 个特定的祖 parent 对象，但我想将它们放入一个选择中

ShapeResults(this IQueryable<SpecificObject>, bool includeParent, bool includeChildren)

方法和我所有的方法都指向带有条件/过滤器的方法。

我在做什么并且效果很好:

var query = context.Grandparent.Select(i => new GrandparentObject
{
    GrandparentProp1 = i.GrandparentProp1 ,
    Parents = i.Parents.Select(j => new ParentObject
    {
        ParentProp1 = j.ParentProp1,
        Children = j.Children.Select(k => new ChildObject
        {
            ChildProp1 = k.ChildProp1,
        }
    }
}

我本质上想做什么

var query = context.Grandparent.Select(i => new GrandparentObject
{
    GrandparentProp1 = i.GrandparentProp1,
--> if (IncludeParents)
    Parents = i.Parents.Select(j => new ParentObject
    {
        ParentProp1 = j.ParentProp1,
    --> if (IncludeParentsChildren)
        Children = j.Children.Select(k => new ChildObject
        {
            ChildProp1 = k.ChildProp1,
        }
    }
}

提前致谢!

Answer 1

如何使用 the conditional operator像这样？

var query = context.Grandparent.Select(i => new GrandparentObject
{
    GrandparentProp1 = i.GrandparentProp1,
    Parents = includeParents
        ? i.Parents.Select(j => new ParentObject
          {
              ParentProp1 = j.ParentProp1,
              Children = includeChildren
                  ? j.Children.Select(k => new ChildObject
                    {
                         ChildProp1 = k.ChildProp1
                    }
                  : Enumerable.Empty<Child>()
          }
        : Enumerable.Empty<Parent>()
};

你也可以使用 null代替 Enumerable.Empty<TResult>() ，这取决于您希望返回结果的语义是什么。

---

编辑: 刚刚意识到我完全想多了这需要多么复杂。像这样尝试:

var query = context.Grandparent.Select(i => new GrandparentObject
{
    GrandparentProp1 = i.GrandparentProp1 ,
    Parents = i.Parents
        .Where(_ => includeParents)
        .Select(j => new ParentObject
    {
        ParentProp1 = j.ParentProp1,
        Children = j.Children
            .Where(_ => includeChildren)
            .Select(k => new ChildObject
        {
            ChildProp1 = k.ChildProp1,
        }
    }
}