实体框架SaveChanges（）不反映在实体上

Question

I have a Winforms project and a database running on SQL Server which has 2 tables, Student and Standard .

First I created an ADO.NET Entity Data Model from the database with the wizard help thing. Then I have a DataGridView control which has a bindingsource as DataSource.

NOTE: DataBindingProjection is a class that I created to be able to populate DataGridView with properties from both Student and Standard entities

I have this code:

var query = context.Students
                  .Include(s => s.Standard)
                  .Select(s => new DataBindingProjection
                  {
                      StudentID = s.StudentID,
                      StudentName = s.StudentName,
                      DateOfBirth = s.DateOfBirth,
                      Height = s.Height,
                      Weight = s.Weight,
                      StandardName = s.Standard.StandardName,
                      Standard_StandardId = s.Standard.StandardId
                  }).ToList();

            myList = new BindingList<DataBindingProjection>(query.ToList());
            dataBindingProjectionBindingSource.DataSource = myList;
            dataBindingProjectionDataGridView.DataSource = dataBindingProjectionBindingSource;

the grid is populated however, when I call context.SaveChanges() , it doesn't update the database.

Answer 1

Using Select method on DbSet to project data to non-entity class will destroy the link to the original data. In your case, you should bind to Student class directly.

To bind to properties in Standard class, you can extends Student by adding property to it because it is a partial class.

partial class Student {
    public StandardName { 
       get { return this.Standard.StandardName; }
       set { this.Standard.StandardName = value; }
    }
}

Assuming that Standard property will never be null.