Data binding linq query to datagridView in Entity

问题:

I am learning the Entity Framework (5.0 and VSExpress 2012) and I'm having real trouble binding my query to a dataGridView in WinForms. I have the below code and it displays my query okay when I start the application but I don't know what I need to do to update the dataGridView after changing the data in the underlying database. What's the best way of doing this? What am I doing wrong here?

private void Form1_Load(object sender, EventArgs e)
    {
        using( var ctx = new TimeKeepEntities())
        {

            var qLoggedIn = from r in ctx.tblTimeRecords
                        where (r.tblEmployee.Active && !r.ClockOut.HasValue) || System.Data.Objects.EntityFunctions.DiffDays(r.ClockOut, DateTime.Now)<30
                        select new { Name = r.tblEmployee.Last + ", " + r.tblEmployee.First, r.tblProject.ProjName, r.ClockIn, r.ClockOut };

            dataGridView1.DataSource = qLoggedIn.ToList();

        }
    }

回答1:

Pho please note that they are using winforms not asp.net. According to MSDN you can do the following:

BindingSource bindingSource1 = new BindingSource();
bindingSource1.DataSource = (from r in ctx.tblTimeRecords
                        where (r.tblEmployee.Active && !r.ClockOut.HasValue) || System.Data.Objects.EntityFunctions.DiffDays(r.ClockOut, DateTime.Now)<30
                        select new { Name = r.tblEmployee.Last + ", " + r.tblEmployee.First, r.tblProject.ProjName, r.ClockIn, r.ClockOut }).ToList();

dataGridView1.DataSource = bindingSource1;

see: msdn documentation

回答2:

You have to bind the data with dataGridView1.DataBind();:

...
dataGridView1.DataSource = qLoggedIn.ToList();
dataGridView1.DataBind();
...

回答3:

.Net uses a disconnected model. When you fetch information from the database, it is a snapshot at that point in time. If you change data in the underlying data store, those changes won't be reflected unless you explicitly re-query the database and rebind your UI.

When you save changes in your UI, EF can check to see if anyone else changed the row that you are modifying (for concurrency concerns) and let you know if there is a potential conflict.

回答4:

 IEnumerable<DataRow> query =( from p in orginalList.AsEnumerable()
                                    where p.Field<long>("Category") == 2
                                    select p).ToList();
                        DataTable boundTable = query.CopyToDataTable<DataRow>();

                        dataGridView1.AutoGenerateColumns = false;

                        dataGridView1.DataSource = boundTable;