Why use AsQueryable() instead of List()?

c# linq repository iqueryable
Keith Adler picture Keith Adler · Jul 10, 2009 · Viewed 51.8k times · Source

I'm getting into using the Repository Pattern for data access with the Entity Framework and LINQ as the underpinning of implementation of the non-Test Repository. Most samples I see return AsQueryable() when the call returns N records instead of List<T>. What is the advantage of doing this?

Answer

Jonathan Allen picture Jonathan Allen · Jul 10, 2009

AsQueryable just creates a query, the instructions needed to get a list. You can make futher changes to the query later such as adding new Where clauses that get sent all the way down to the database level.

AsList returns an actual list with all the items in memory. If you add a new Where cluse to it, you don't get the fast filtering the database provides. Instead you get all the information in the list and then filter out what you don't need in the application.

So basically it comes down to waiting until the last possible momment before committing yourself.

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