Problem passing in Func as parameter to Where clause

Question

I have this simple 2 lines of following code. It compiles fine but never return results in the datagridview. If I change func to p=> p.PTNT_FIRST_NAME.StartsWith(this.textBox1.Text), it works just fine. What's the problem here?

Func<PATIENT, bool> func = (PATIENT p) => p.PTNT_FIRST_NAME.StartsWith(this.textBox1.Text);
this.dataGridView1.DataSource = dataContext.PATIENTs.Where<PATIENT>(func).Select(q => q);

Answer 1

Change Func<PATIENT, bool> to Expression<Func<PATIENT, bool>>.

Answer 2

Try this:

Expression<Func<PATIENT, bool>> func = (PATIENT p) => p.PTNT_FIRST_NAME.StartsWith(this.textBox1.Text);

Answer 3

It works. But what's the cause of the problem? Why it compiles fine and Where does accept Func as parameter.