Entity Framework Tutorial Basics（26）：Add Entity Graph

追憶似水流年發表於2016-07-07
Framework

Add Entity Graph using DbContext:

Adding entity graph with all new entities is a simple task. We can use DbSet.Add() method to attach a whole entity graph to the context and set all the entity's states to Added as we have seen in theprevious section.

The following example adds a student entity graph in disconnected mode, using the DbSet.Add() method which marks the added state to all the entities:

//Create student in disconnected mode
Student newStudent = new Student() { StudentName = "New Single Student" };
            
//Assign new standard to student entity
newStudent.Standard = new Standard() { StandardName = "New Standard" };
            
//add new course with new teacher into student.courses
newStudent.Courses.Add(new Course() { CourseName = "New Course for single student", Teacher = new Teacher() { TeacherName = "New Teacher" } });

using (var context = new SchoolDBEntities())
{
    context.Students.Add(newStudent);
    context.SaveChanges();

    Console.WriteLine("New Student Entity has been added with new StudentId= " + newStudent.StudentID.ToString());
    Console.WriteLine("New Standard Entity has been added with new StandardId= " + newStudent.StandardId.ToString());
    Console.WriteLine("New Course Entity has been added with new CourseId= " + newStudent.Courses.ElementAt(0).CourseId.ToString());
    Console.WriteLine("New Teacher Entity has been added with new TeacherId= " + newStudent.Courses.ElementAt(0).TeacherId.ToString());
}

 

Output:

New Student Entity has been added with new StudentId= 14 
New Standard Entity has been added with new StandardId= 6
New Course Entity has been added with new CourseId= 7
New Teacher Entity has been added with new TeacherId= 9

This executes the following DDL statements to the database:

exec sp_executesql N'INSERT [dbo].[Standard]([StandardName], [Description])
VALUES (@0, NULL)
SELECT [StandardId]
FROM [dbo].[Standard]
WHERE @@ROWCOUNT > 0 AND [StandardId] = scope_identity()',N'@0 varchar(50)',@0='New Standard'
go

exec sp_executesql N'INSERT [dbo].[Student]([StudentName], [StandardId])
VALUES (@0, @1)
SELECT [StudentID]
FROM [dbo].[Student]
WHERE @@ROWCOUNT > 0 AND [StudentID] = scope_identity()',N'@0 varchar(50),@1 int',@0='New Single Student',@1=61
go

exec sp_executesql N'INSERT [dbo].[Teacher]([TeacherName], [StandardId])
VALUES (@0, NULL)
SELECT [TeacherId]
FROM [dbo].[Teacher]
WHERE @@ROWCOUNT > 0 AND [TeacherId] = scope_identity()',N'@0 varchar(50)',@0='New Teacher'
go

exec sp_executesql N'INSERT [dbo].[Course]([CourseName], [Location], [TeacherId])
VALUES (@0, NULL, @1)
SELECT [CourseId]
FROM [dbo].[Course]
WHERE @@ROWCOUNT > 0 AND [CourseId] = scope_identity()',N'@0 varchar(50),@1 int',@0='New Course for single student',@1=93
go

exec sp_executesql N'INSERT [dbo].[StudentCourse]([StudentId], [CourseId])
VALUES (@0, @1)
',N'@0 int,@1 int',@0=43,@1=72
go

 

Thus, there is no difference when you add a single entity or entity graph in disconnected or connected scenario. Make sure that all the entities are new.

Learn how to update entity graph in disconnected scenario in the next section.

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