EntityFramework 学习 一 Disconnected Entities

如何把断开的实体添加到新的context上下文中

1.首先，我们需要把实体附加到新的context上下文实例中。

2.其次，手动的给实体设置适当的实体状态，因为新的context上下文不知道断开的实体上有什么操作。

DbSet.Add():

把实体添加到context上下文，并自动设置实体的属性为added状态

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

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

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

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

DbSet.Attach():

把实体添加到context中，并设置为Unchanged状态

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

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

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

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

通过DBContext.Entry()方法获取指定实体的状态，

DbContext.Entry(disconnectedEntity).state = EntityState.Added/Modified/Deleted/Unchanged

Parent Entity State	Entity State of child entities
Added	Added
Modified	Unchanged
Deleted	All child entities will be null