如何热切地将实体的子孙元素包括在实体框架代码中？ [英] How do I eagerly Include the child and grandchild elements of an entity in Entity Framework Code First?

问题描述

想象一下这三个实体（客户，书籍，作者）相关：

Imagine three entities (Customer, Book, Author) related like this:

客户有很多图书

一本书有一个作者

我使用这些数据打印如下报告：

I use that data to print a report like this:

Customer: Peter
  Book: To Kill a Mockingbird - Author: Harper Lee
  Book: A Tale of Two Cities - Author: Charles Dickens
Customer: Melanie
  Book: The Hobbit - Author: J. R. R. Tolkien

当我查询我得到的客户时，如预期，一堆以下性质的查询

When I query for Customers I get, as expected, a bunch of queries of the following nature

1. 查询以获取客户


2. 查询每个客户获取他的书籍


3. 每本书查询以获取作者

我可以通过包含这些书籍来减少查询数量：

I can reduce the number of queries by including the books like so:

var customers = db.Customers.Include（c => c.Books）;

var customers = db.Customers.Include(c => c.Books);

但是我不知道如何加载第三级（作者）。我该怎么做？

But I don't know how to load the third level (Author). How can I do that?

推荐答案

包含接受可以表示您需要的任何额外属性的完整路径的字符串：

There's an overload for Include that accepts a string which can denote the full path to any extra properties you need:

var customers = db.Customers.Include("Books.Author");

看起来很奇怪，因为作者不是书籍集合（而是属性）的属性在每本书上），但它的作品。给它一个旋转。

It looks strange because "Author" isn't a property on a collection of books (rather a property on each individual book) but it works. Give it a whirl.

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