LINQ 包含 select 的子数组

Question

我有以下运行良好的 LINQ 查询：

public IList<Course> GetEmployeeCourses(int id) {
  var employeeCourses = Context.Employees
    .Where(e => e.Id == id)
    .SelectMany(e => e.employeeCourses.Select(ec => ec.Course))
    .ToList();

  return employeeCourses;
}

问题是，我现在还需要在返回 Course 数组时包含所选课程的子数组 (Urls)。

类似：

public IList<Course> GetEmployeeCourses(int id) {
  var employeeCourses = Context.Employees
    .Where(e => e.Id == id)
    .SelectMany(e => e.employeeCourses.Select(ec => ec.Course))
    .Include(c => c.Urls)
    .ToList();

  return employeeCourses;
}

这样返回 JSON：（尽管 Course 模型有超过 15 个属性）

[
  {
     "Name": "Course1",
     "Type": "Maths",
     "Location": "Block C",
     "Urls": [
          {
            "Link": "https://url1forcourse1.com"
          },
          {
            "Link": "https://url2forcourse1.com"
          }
      ]
  }
  {
     "Name": "Course2"
     "Type": "Computer Science",
     "Location": "Block A",
     "Urls": [
          {
            "Link": "https://url1forcourse2.com"
          },
          {
            "Link": "https://url2forcourse2.com"
          }
      ]
  },
  {
     "Name": "Course3"
     "Type": "The Art of Dish Washing",
     "Location": "Block E",
     "Urls": [
          {
            "Link": "https://url1forcourse3.com"
          },
          {
            "Link": "https://url2forcourse3.com"
          }
      ]
  }
]

如何以最有效的方式实现这一目标？目前我似乎根本无法获取名为“Urls”的子数组，它始终为空。

另外，我正在使用 Fluent API 和这个 EmployeeCourse 配置：

ToTable("EmployeeCourses");

HasKey(q => new { q.CourseId, q.Employee.Id})

HasRequired(x => x.Employee)
   .WithMany(x => x.EmployeeCourses)
   .HasForeignKey(x => x.CourseId);

HasRequired(x => x.Course)
   .WithMany(x => x.EmployeeCourses)
   .HasForeignKey(x => x.EmployeeId);

Answer 1

来自Eagerly loading multiple levels：

预加载是查询一种类型的实体的过程 还加载相关实体作为查询的一部分。急切加载是 使用 Include 方法实现。

你可以这样尝试，因此它可以让你加载所有EmployeeCourses和相关的Courses

public IList<Course> GetEmployeeCourses(int id) {
  var employeeCourses = Context.Employees
    .Where(e => e.Id == id)
    .Include(e => e.employeeCourses.Select(ec => ec.Course))
    .SelectMany(e => e.employeeCourses.Select(ec => ec.Course))
    .ToList();

  return employeeCourses;
}

Answer 2

您可能喜欢使用链式SelectMany 作为：

public IList<Course> GetEmployeeCourses(int id)
{
  var employeeCourses = Context.Employees
                        .Where(e => e.Id == id)
                        .SelectMany(e => e.employeeCourses
                        .SelectMany(ec => ec.Course))
                        .Include(c => c.Urls)
                        .ToList();



    return employeeCourses;
}