包含扩展方法的类库参考

Question

I am reading a tutorial http://www.asp.net/mvc/overview/getting-started/getting-started-with-ef-using-mvc/reading-related-data-with-the-entity-framework-in-an-asp-net-mvc-application

There I found some code like

viewModel.Instructors = db.Instructors
    .Include(i => i.OfficeAssignment)

I like to understand the .Include method. Where is the reference? (I am expecting something like class library reference)

Answer 1

To better understand how it's working, let's take these sample Entity classes:

 public class Student
{
    public Student() { }

    public int StudentId { get; set; }
    public string StudentName { get; set; }
    public virtual StudentAddress StudentAddress { get; set; }
    public virtual ICollection<Teacher> Teachers { get; set; }
}

public class StudentAddress 
{
    [Key, ForeignKey("Student")]
    public int StudentId { get; set; }

    public string Address1 { get; set; }
    public string Address2 { get; set; }
    public string City { get; set; }
    public int Zipcode { get; set; }
    public string State { get; set; }
    public string Country { get; set; }

    public virtual ICollection<StudentAddressDetail> StudentAddressDetails { get; set; }

    public virtual Student Student { get; set; }
}

Eager Loading

The Eager Loading function is useful when you want to load the main Entity (or Entity collection) together with its related entities right from the start, possibly using a single query command. In order to use that you need to use the Include() method in the following way:

using (var ctx = new SchoolDBEntities())
{
    // Loads the students AND all related StudentAddress using Eager Loading
    IList<Student> sList = ctx.Students.Include(s => s.StudentAddress).ToList<Student>();
    Student s = sList[0];
}

IMPORTANT : If you can't find the Include() method, check that you added the System.Data.Entity namespace.

You can also use Eager Loading to load nested, multi-level properties. For example, we could load the StudentAddressDetails collection property of each StudentAddress item (cfr. the StudentAddress class definition above) in the following way:

using (var ctx = new SchoolDBEntities())
{
    // Loads the students AND all related StudentAddress AND all related StudentAddressDetails using Eager Loading
    IList<Student> sList = ctx.Students.Include(s => s.StudentAddress.StudentAddressDetails).ToList<Student>();
    Student s = sList[0];
}

This has been well explained here . The answer above is an extract from this post:

Answer 2

Add a using System.Data.Entity; in your file.