I'm new to the Entities Framework, and am just starting to play around with it in my free time. One of the major questions I have is regarding how to handle ObjectContexts.
Which is generally preferred/recommended of these:
This
public class DataAccess{
MyDbContext m_Context;
public DataAccess(){
m_Context = new MyDbContext();
}
public IEnumerable<SomeItem> GetSomeItems(){
return m_Context.SomeItems;
}
public void DeleteSomeItem(SomeItem item){
m_Context.DeleteObject(item);
m_Context.SaveChanges();
}
}
Or this?
public class DataAccess{
public DataAccess(){ }
public IEnumerable<SomeItem> GetSomeItems(){
MyDbContext context = new DbContext();
return context.SomeItems;
}
public void DeleteSomeItem(SomeItem item){
MyDbContext context = new DbContext();
context.DeleteObject(item);
context.SaveChanges();
}
}
Best Answer
The ObjectContext is meant to be the "Unit of Work".
Essentially what this means is that for each "Operation" (eg: each web-page request) there should be a new ObjectContext instance. Within that operation, the same ObjectContext should be re-used.
This makes sense when you think about it, as transactions and change submission are all tied to the ObjectContext instance.
If you're not writing a web-app, and are instead writing a WPF or windows forms application, it gets a bit more complex, as you don't have the tight "request" scope that a web-page-load gives you, but you get the idea.
PS: In either of your examples, the lifetime of the ObjectContext will either be global, or transient. In both situations, it should NOT live inside the DataAccess class - it should be passed in as a dependency