Anon Anon - 1 year ago 223
C# Question

DataGridView is editable but does not send changes back to database using Entity Framework

I've bound my

to my
so that whatever value is selected in the
, the corresponding valued for SID and Mark will appear in the
. The
is editable when I do this but the data is not saved in the database when it is input. Is there a way to update it? If there's another method, I have to first warn that I only need SID and Mark in the
, if I try to bind the whole "Student_Course" table to the
I get other columns I don't need.

private void cboeCID_SelectedIndexChanged_1(object sender, EventArgs e)
var CID = Convert.ToInt32(cboeCID.Text);
using (var db = new Entities2())
var course = from c in db.Student_Course
where c.CID == CID
select new Class1
SID = c.SID,
Mark = c.Mark
editDataGridView.DataSource = course.ToList();

class Class1
public int SID { get; set; }
public int Mark { get; set; }


Answer Source

There are some important issues in above code:

  1. You shaped the result of query to a custom Class1 which is not your entity type.

  2. You used a DbContext in using statement which means db is disposed after the using statement and will not track changes.

  3. You called SaveChanges on another instance of your DbContext which is not aware of changes, so nothing happens.

To solve above issues consider these tips:

  1. Create db as a field of Form and instantiate it in Load event of Form and use it for both loading and saving data.
  2. You can load data entity this way:

    db = new Entities2();
    db.Student_Course.Where(x => c.CID== CID).ToList();
    editDataGridView.DataSource = db.Student_Course.Local; 
  3. You can save data this way:

  4. If you need to use a view model different than your entity for edit, when saving changes you should first load original entities from database using another instance of your context, then for each entity set the value of changed field and then call SaveChanges method.

For more information take a look at these resources:

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