Does “foreach” cause repeated Linq execution?

Question

I\'ve been working for the first time with the Entity Framework in .NET, and have been writing LINQ queries in order to get information from my model. I would like to progr

Answer 1

The difference is in the underlying type. As LINQ is built on top of IEnumerable (or IQueryable) the same LINQ operator may have completely different performance characteristics.

A List will always be quick to respond, but it takes an upfront effort to build a list.

An iterator is also IEnumerable and may employ any algorithm every time it fetches the "next" item. This will be faster if you don't actually need to go through the complete set of items.

You can turn any IEnumerable into a list by calling ToList() on it and storing the resulting list in a local variable. This is advisable if

• You don't depend on deferred execution.
• You have to access more total items than the whole set.
• You can pay the upfront cost of retrieving and storing all items.