Getting the most out of Entity Framework in a ASP MVC web application

Question

How do I get the most out of my Entity Framework (v4.0 or better) in my ASP MVC3 web application? My main problem is due to the request-response nature of the web, it seems I have to manually track objects being displayed on a form to the DB in order to do CUD operations. Eg. as suggested in Editing and Updating Entity Framework entity in ASP .NET MVC this seems awfully manual. Is there a way to keep my context in my session some how such that EF is doing all the work for me?

Answer 1

Don't store ObjectContext in session. Use a new context for each request processing. Here you can read something about long living contexts. If you use long living context stored in session you will have a big problem to load fresh data. Also if your user opens your application in multiple browser tabs (= same session) you can get some very unexpected results.

If you want to update just scalar values (no changes in navigation properites) you can use:

Insert scenario:

[HttpPost]
public ActionResult Insert(MyEntity entity)
{
    using (var context = new MyContext())
    {
        context.MyEntities.AddObject(entity);
        context.SaveChanges(); 
    }

    ...
}

Update scenario with fully detached object:

[HttpPost]
public ActionResult Update(MyEntity entity)
{
    using (var context = new MyContext())
    {
        context.MyEntities.Attach(entity);
        context.ObjectStateManager.ChangeObjecState(entity, EntityState.Modified);
        context.SaveChanges(); 
    }

    ...
}

Update scenario with loading object first from DB:

[HttpPost]
public ActionResult Update(MyEntity entity)
{
    using (var context = new MyContext())
    {
        int id = entity.Id;
        context.MyEntities.Single(e => e.Id == id); // You must load the record first
        context.MyEntities.ApplyCurrentValues(entity);
        context.SaveChanges(); 
    }

    ...
}

Delete scenario:

[HttpPost]
public ActionResult Delete(int id)
{
    using (var context = new MyContext())
    {
        var entity = context.MyEntities.Single(e => e.Id == id);
        context.MyEntities.DeleteObject(entity);
        context.SaveChanges(); 
    }

    ...
}

It is possible to delete the entity without loading it first but if the entity has any relation it couses a lot of troubles.

If you want to modify relations as well it can involve using either UpdateMode / TryUpdateModel as discussed here or tracking changes manually as described here. Simple relation updates on Foreign key association (the description is the same even if you don't use code-first) can be still handled by previous examples.