IQueryable vs IEnumerable

The primary difference is that the extension methods defined for IQueryable take Expression objects instead of Functional objects, meaning the delegate it receives is an expression tree instead of a method to invoke.

IEnumerable < T > is great for working with in-memory collections, but IQueryable< T > allows for a remote data source, like a database or web service.

IEnumerable doesn’t have the concept of moving between items, it is a forward only collection. It’s very minimalistic; something that most any data source can provide. Using only this minimal functionality, LINQ can provide all of these great operators.

IQueryable<T> is a very powerful feature that enables a variety of interesting deferred execution scenarios (like paging and composition based queries).


IQueryable < Customer > custs = from c in db.Customers
where c.City == "< City >"
select c;

IEnumerable < Customer> custs = from c in db.Customers
where c.City == "< City >"
select c;