在实体上显式加载多个引用/集合 [英] Explicit loading of multiple references/collections on entity

问题描述

考虑以下实体模型：

public class Parent
{
    public virtual FirstChild FirstChild { get; set; }
    public virtual SecondChild SecondChild { get; set; }
}

在我的代码中，我加载了 / code>实体：

In my code, I have loaded Parent entity:

Parent parent = <loaded in some way>;

要显式加载其导航属性，我使用

To explicitly load its navigational properties, I use

db.Entry(parent).Reference(p => p.FirstChild).Load();
db.Entry(parent).Reference(p => p.SecondChild).Load();

但这会导致两个DB查询。

But this results in two DB queries.

问题：是否有更优雅的方式，这将允许在单个查询中显式加载多个导航属性？

如果我没有加载 parent ，我会热切加载：

If I didn't have parent loaded, I would do eager loading:

Parent parent = db.Parents
    .Include(p => p.FirstChild)
    .Include(p => p.SecondChild)
    .FirstOrDefault();

但是，正如我所提到的，我已经加载了没有相关实体（而且我无法修改

but, as I mentioned, I already have it loaded without related entities (and I can't modify the loading code).

推荐答案

唯一可能的方法是（afaik）重新加载父属性。假设变量 parent 附加到上下文中：

The only possible way (afaik) is to reload the parent property. Assuming the variable parent is attached to the context:

var tmp = db.Parents
    .Include(p => p.FirstChild)
    .Include(p => p.SecondChild)
    .FirstOrDefault(p => p.Equals(parent));

// tmp and parent are the same instance now!
var isTrue = ReferenceEquals(tmp, parent);

var child1 = parent.FirstChild;  // is already loaded
var child2 = parent.SecondChild; // is already loaded

这是有效的，因为上下文会检测到你正在寻找的实体被加载并且已经附加，因此不会创建一个新的，而是更新旧的（父在这种情况下）。

This works, because the context will detect that entity you are looking for is loaded and attached already and therefore not create a new one but rather update the old one (parent in this case).

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