Linq deferred execution in asp.net - asp.net

Question

My dbml contains a master table "M" and a detail table "D1".
My aspx page consists of a TextBox to show M data and a grid to populate with D1 data. I want the grid to populate when a button is clicked to save loading time (D1 contains a lot of rows).
Question 1: Is the following code the correct way to do it?
protected void Page_Load(object sender, EventArgs e)
{
MyDataContext context = new MyDataContext();
M m = context.Ms.Single(n => n.id == id); // id is somehow provided
TextBox1.Text = m.field1;
}
protected void Button1_Click(object sender, EventArgs e)
{
MyDataContext context = new MyDataContext();
M m = context.Ms.Single(n => n.id == id); // id is somehow provided
Grid1.DataSource = m.D1s;
Grid1.DataBind();
}
Question 2: Since I can access m.D1s in Page_Load does this mean the detail data is already fetched from the database anyway or does deferred execution apply?

Answer 1

Unless you explicitly load the children, they will be deferred loaded. If in question, try attaching a profiler to your requests and debug into the program to see when the queries are issued.
If you want to eager load the children in LINQ to SQL, use the LoadOptions with the LoadWith operation.
protected void Button1_Click(object sender, EventArgs e)
{
MyDataContext context = new MyDataContext();
var lo = new DataLoadOptions();
lo.LoadWith<M>(m => m.D1s);
context.LoadOptions = lo;
M m = context.Ms.Single(n => n.id == id); // id is somehow provided
Grid1.DataSource = m.D1s;
Grid1.DataBind();
}
In this case, if you don't need the m since it was already set in the page load, just load the appropriate D1s without reloading M in the button click handler:
protected void Button1_Click(object sender, EventArgs e)
{
using (MyDataContext context = new MyDataContext())
{
IQueryable<D> D = context.D1s.Where(d => d.Mid == id);
// id is somehow provided
Grid1.DataSource = D;
Grid1.DataBind();
}
}