MVC2 && EF4.0 Cascading Drop Down List

I am trying to create a cascading drop down in MVC2. This is a simple application so I am using Entity Framework 4.0 classes in my User Layer (instead of the usual POCOs).

I looked at Steve’s Walther’s solution(s) here: the problem is that it doesn’t work – you get an object null reference b/c the page isn’t done loading (I think). I tried putting it into JQuery, which I know waits to fire until the DOM is loaded, but I started getting too deep into the port.

I then looked at other people’s attempts like here and here – lots of code, little explanation and it doesn’t work without modifications.

I then went back to a project that I created does an Ajax call for the second drop down and tried to create my own solution.

Here is the initial controller:

1 public JsonResult GetDoctrinesForAnIssue(int issueId) 2 { 3 IDoctrineFactory doctrineFactory = new DoctrineFactory(); 4 List<Doctrine> doctrines = doctrineFactory.GetDoctrines(issueId); 5 return Json(doctrines.ToList()); 6 } 7  

The problem is that I am using an EF class directly in the JSON return. I am getting a missing object context because the entire graph is not loading and the context is disposed when it is going back to rehydrate – one of limitations of EF is that the instantiated class has to exist with the object context that created it so when that context goes away, you are stuck.

image

When I put the entire graph in to see, I got a circular reference error. Ugh

1 var doctrineQuery = (from doctrine in patentEntities.Doctrines 2 .Include("Issue") 3 .Include("Comment") 4 .Include("Comment.Claim") 5 .etc…. 6 select doctrine).ToList<Doctrine>(); 7 return doctrineQuery; 8  

I then thought about some of my other projects that I have worked on lately. I used POCOs extensively so this kind of problem didn’t surface – the downside is that I would then need to code up the POCOs, the Factories, and the mapping between the POCOs and EF classes – which is a bit overkill for this project. I then thought of a third way of using a dynamic object just for this drop down lists – outside of the factory, inside the controller:

1 public JsonResult GetDoctrinesForAnIssue(int issueId) 2 { 3 IDoctrineFactory doctrineFactory = new DoctrineFactory(); 4 var query = (from doctrine in doctrineFactory.GetDoctrines(issueId) 5 select new { doctrine.DoctrineId, doctrine.DoctrineName }).ToList(); 6 7 return Json(query); 8 } 9  

Add a little LINQ and boom goes the dynamite…

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