Foreign key relationships in Entity Framework
- by Anders Svensson
I'm trying to add an object created from Entity Data Model classes. I have a table called Users, which has turned into a User EDM class. And I also have a table Pages, which has become a Page EDM class. These tables have a foreign key relationship, so that each page is associated with many users. Now I want to be able to add a page, but I can't get how to do it. I get a nullreference exception on Users below. I'm still rather confused by all this, so I'm sure it's a simple error, but I just can't see how to do it.
Also, by the way, the compiler requires that I set PageID in the object initializer, even though this field is set to be an automatic id in the table. Am I doing it right just setting it to 0, expecting it to be updated automatically in the table when saved, or how should I do that?
Any help appreciated!
The method in question:
private Page GetPage(User currentUser)
{
string url = _request.ServerVariables["url"].ToLower();
var userPages = from p in _context.PageSet
where p.Users.UserID == currentUser.UserID
select p;
var existingPage = userPages.FirstOrDefault(e => e.Url == url); //Could be combined with above, but hard to read?
if (existingPage != null)
return existingPage;
Page page = new Page()
{
Count = 0,
Url = _request.ServerVariables["url"].ToLower(),
PageID = 0, //Only initial value, changed later?
};
_context.AddToPageSet(page);
page.Users.UserID = currentUser.UserID; //Here's the problem...
return page;
}
