Methods to Attach Disconnected Entities in EF 6

Here you will learn about different methods in Entity Framework 6.x that attach disconnected entity graphs to a context.

Saving an entity in the disconnected scenario is different than in the connected scenario. There are two things we need to do when we get a disconnected entity graph or even a single disconnected entity. First, we need to attach entities with the new context instance and make the context aware about these entities. Second, set an appropriate EntityState to each entity manually because the instance doesn't know anything about the operations performed on the disconnected entities, so it cannot apply the appropriate EntityState automatically.

The following figure illustrates this process.

Entity Framework provides the following methods that attach disconnected entities to a context and also set the EntityState to each entity in an entity graph.

• DbContext.Entry()
• DbSet.Add()
• DbSet.Attach()

DbContext.Entry()

The Entry() method of DbContext class returns an instance of DbEntityEntry for the specified entity. The DbEntityEntry object provides various information about the specified entity and also the ability to perform an action on the entity. Most importantly, we can change the EntityState of the specified entity using State property, as shown below.

context.Entry(entity).state = EntityState.Added/Modified/Deleted

The Entry method attaches an entire entity graph to a context with the specified state to a parent entity and also sets a different EntityState to other entities. Consider the following example.

var student = new Student() { //Root entity (empty key)
        StudentName = "Bill",
        StandardId = 1,
        Standard = new Standard()   //Child entity (with key value)
                    {
                        StandardId = 1,
                        StandardName = "Grade 1"
                    },
        Courses = new List<Course>() {
            new Course(){  CourseName = "Machine Language" }, //Child entity (empty key)
            new Course(){  CourseId = 2 } //Child entity (with key value)
        }
    };

using (var context = new SchoolDBEntities())
{
    context.Entry(student).State = EntityState.Added; 

    foreach (var entity in context.ChangeTracker.Entries()){
        Console.WriteLine("{0}: {1}", entity.Entity.GetType().Name, entity.State);
    } 
}

Student: Added
Standard: Added
Course: Added
Course: Added

In the above example, the Studnet entity graph includes the Standard and Course entities. context.Entry(student).State = EntityState.Added; sets the Added state to the parent entity as well as to all other child entities irrespective of whether a child entity contains an empty key value or not. Thus, it is recommended to use the Entry() method carefully.

The following table lists the behaviour of the Entry() method.

DbSet.Add()

The DbSet.Add() method attaches the entire entity graph to a context and automatically applies the Added state to all entities.

//disconnected entity graph
Student disconnectedStudent = new Student() { StudentName = "New Student" };
disconnectedStudent.StudentAddress = new StudentAddress() { Address1 = "Address", City = "City1" };

using (var context = new SchoolDBEntities())
{
    context.Students.Add(disconnectedStudent);
                
    // get DbEntityEntry instance to check the EntityState of specified entity
    var studentEntry = context.Entry(disconnectedStudent);
    var addressEntry = context.Entry(disconnectedStudent.StudentAddress);

    Console.WriteLine("Student: {0}", studentEntry.State);
    Console.WriteLine("StudentAddress: {0}", addressEntry.State);
}

Student: Added
StudentAddress: Added

The DbSet.Add() method attaches the entire entity graph to a context with the Added state to each entity. Calling context.Savechanges() will execute the INSERT command for all the entities, which will insert new records in the appropriate database table.

DbSet.Attach()

The DbSet.Attach() method attaches an entire entity graph to the new context with the Unchanged entity state.

//disconnected entity graph
Student disconnectedStudent = new Student() { StudentName = "New Student" };
disconnectedStudent.StudentAddress = new StudentAddress() { Address1 = "Address", City = "City1" };

using (var context = new SchoolDBEntities())
{
    context.Students.Attach(disconnectedStudent);
                
    // get DbEntityEntry instance to check the EntityState of specified entity
    var studentEntry = context.Entry(disconnectedStudent);
    var addressEntry = context.Entry(disconnectedStudent.StudentAddress);

    Console.WriteLine("Student: {0}",studentEntry.State);
    Console.WriteLine("StudentAddress: {0}",addressEntry.State);
}

Student: Unchanged
StudentAddress: Unchanged