DataGridView AllowUserToAddRow property doesn't work

Question

I have a simple project with Entity Framework, I have a DataGridView in my Form and I set its AllowUserToAddRow property to true but still I can not add new rows into it.

And here is my code:

DBEntities context = new DBEntities();
private void Form1_Load(object sender, EventArgs e)
{
    var q = (from i in context.myTable
             select i).ToList();
    DataGridView.DataSource = q;
}

private void btnSave_Click(object sender, EventArgs e)
{
    context.SaveChanges();
    MessageBox.Show("saved successfully");
}

If I use a BindingSource control, it allow me to insert rows in DataGridView but with this approach after I call context.SaveChanges() nothing insert in my database file. So I thought maybe its relative to this problem that DataGridView with true AllowUserToAddRow property doesn't let me to insert row in DataGridView.

Answer 1

Your problem is that you call .ToList() and materialize your query - this appears to break the full databinding.

You should be able to simply have:

DBEntities context = new DBEntities();
private void Form1_Load(object sender, EventArgs e)
{
    var q = (from i in context.myTable
             select i);
    DataGridView.DataSource = q;
}

I tried this and it works fine for allowing new rows (you do need to have a primary key in your table but you should have that anyway).

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Do Note: this behaviour has been intentionally broken in Entity Framework 4.1 - Webforms data binding with EF Code-First Linq query error

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I say should in my answer because I'm actually a little surprised it is this easy. I recall it not working so nicely in earlier versions of Entity Framework and I haven't used 4.0 very much.

If the solution above doesn't work you may have to do this the hard way and add new objects yourself before saving:

First introduce a binding source and when you save do something like (with an imaginary entity of Customer in the example):

foreach (Customer customer in bs.List)
{         
    // In my db customerId was an identity column set as primary key
    if (customer.CustomerId == 0)
        context.Customers.AddObject(customer);
}
context.SaveChanges();