[C#] Func vs Expression Func

今天在找一個Performance issue時， 打開Sql profiler突然看到一段EF查詢直接做Full table scan， 追了一下原來是傳過去的條件型態宣告為： Func<T,bool> ；  注意Func在Linq或lambda expression中並無法直接轉為sql，必須改為傳遞Expression<Func<T>>。

Difference between Func<T> and Expression<Func<T>>

If you want your lambda to be executed in SQL, you need to pass it as an Expression, not a Function.

http://stackoverflow.com/a/31368798/7045253

Func<T> denotes a delegate which is pretty much a pointer to a method and Expression<Func<T>> denotes a tree data structure for a lambda expression.

http://stackoverflow.com/a/793584/7045253