EF LINQ包含多个嵌套实体

Question

好的,我有三层实体,具有以下层次结构:课程 - >模块 - >章节

这是最初的EF LINQ声明:

Course course = db.Courses
                .Include(i => i.Modules.Select(s => s.Chapters))
                .Single(x => x.Id == id); 

现在,我想要包含另一个名为Lab的实体,该实体与课程相关联.

如何包含实验室实体？

我尝试了以下但它不起作用:

Course course = db.Courses
                .Include(i => i.Modules.Select(s => s.Chapters) && i.Lab)
                .Single(x => x.Id == id); 

关于包含第二实体的任何想法？

任何建议或信息都将受到高度赞赏.谢谢!

Answer 1

你试过添加另一个Include:

Course course = db.Courses
                .Include(i => i.Modules.Select(s => s.Chapters))
                .Include(i => i.Lab)
                .Single(x => x.Id == id);

您的解决方案失败,因为Include不采用布尔运算符

Include(i => i.Modules.Select(s => s.Chapters) &&          i.Lab)
                           ^^^                  ^             ^ 
                          list           bool operator    other list

更新 要了解更多信息,请下载LinqPad并查看示例.我认为这是熟悉Linq和Lambda的最快捷方式.

作为一个开始-之间差异Select和Include是与一个选择,你决定什么要返回(又名投影).Include是一个Eager Loading函数,它告诉Entity Framework您希望它包含来自其他表的数据.

Include语法也可以是字符串.像这样:

           db.Courses
            .Include("Module.Chapter")
            .Include("Lab")
            .Single(x => x.Id == id);

但是LinqPad的样本更好地解释了这一点.

Answer 2

Include是流畅的接口的一部分,因此您可以编写多个Include语句,每个语句跟随其他语句

 db.Courses.Include(i => i.Modules.Select(s => s.Chapters))
           .Include(i => i.Lab)
           .Single(x => x.Id == id); 

Answer 3

在Entity Framework Core(EF.core)中,您可以使用.ThenInclude包含下一级别.

var blogs = context.Blogs
    .Include(blog => blog.Posts)
        .ThenInclude(post => post.Author)
    .ToList();

更多信息:https://docs.microsoft.com/en-us/ef/core/querying/related-data

注意: 假设您需要ThenInclude()打开多个blog.Posts,只需重复Include(blog => blog.Posts)并执行另一个操作ThenInclude(post => post.Other).

var blogs = context.Blogs
    .Include(blog => blog.Posts)
        .ThenInclude(post => post.Author)
    .Include(blog => blog.Posts)
        .ThenInclude(post => post.Other)
 .ToList();

Answer 4

你也可以试试

db.Courses.Include("Modules.Chapters").Single(c => c.Id == id);

Answer 5

可以编写这样的扩展方法：

    /// <summary>
    /// Includes an array of navigation properties for the specified query 
    /// </summary>
    /// <typeparam name="T">The type of the entity</typeparam>
    /// <param name="query">The query to include navigation properties for that</param>
    /// <param name="navProperties">The array of navigation properties to include</param>
    /// <returns></returns>
    public static IQueryable<T> Include<T>(this IQueryable<T> query, params string[] navProperties)
        where T : class
    {
        foreach (var navProperty in navProperties)
            query = query.Include(navProperty);

        return query;
    }

即使在通用实现中也像这样使用它：

string[] includedNavigationProperties = new string[] { "NavProp1.SubNavProp", "NavProp2" };

var query = context.Set<T>()
.Include(includedNavigationProperties);