Loading a context

Question

Have I understood this correctly please.

When you are running a web application to view pages and you create an instance of the context is that instance loading all the database date into it?

If it does does that not take up a lot of memory a blog with five years of blogs could have 1,500 to 2,000 (or more)post in it, with all the comments tags etc that would be a great deal of data.

So what does happen when you create the instance of a context?

Answer 1

A context only loads the records that you request, so when you first instantiate one it will be empty and won't perform any queries against the database until you tell it to. Any entities you load through it will (usually) be cached within the context, though, so they use more and more memory every time you run a query and can become very large over time.

For that reason, and because contexts are relatively cheap to instantiate, it's a good idea to only keep them alive while you actually need them, and dispose of them as soon as you're done. This is part of the "unit of work" pattern -- basically using a new context for each set of operations that go together as one unit or transaction.

Edited to add:

If you're performing read-only queries (i.e. you just want to display data, you don't need to make changes and save them back to the database), you might check out non-tracking queries (e.g. the .AsNoTracking() method if you're using a DbContext/DbSet, or the MergeOption.NoTracking property if you're using an ObjectContext/ObjectSet) -- that will avoid caching the results in the context, increasing performance and reducing memory use.