Insertion into database using entity framework in n-tier architecture

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ASP.NET

Hi.....
I have 3 column in may table. Id primary key and identity key,status default value false,feedback.

I want insert value only in feedback using entity framework in n-tier arct.

First of all i made Bo class such as private int id; pubic int id{get,set}
Now I made DAL class where I made function using(ENAme context=new Ename)
Tablename tt=new Tablename
context.addtotalename(tt)
context.savechanges();

Now I made BAL class whaere I call DAL function.In mu aspx.cs page I did work on click on button

Bo aa=new BO();
aa.feedback=Textbox1.text;
bal ss=new bal();
ss.insert(aa)





My error is that cannot insert the null into 'feedback'.