Question

I’ve noticed that certain command cause LINQtoSQL to connect to the database and download the records that are part of the query, for example, .ToArray().

Does the command .Cast() cause a query to execute (and how can I tell these things in the future?). For example…

IRevision<T> current = context.GetTable(typeof(T))     .Cast<IRevision<T>>()     .SingleOrDefault(o => o.ID == recordId); 

I know there is a command for .GetTable that allows you to specify a generic type, but for strange and unexplainable reasons, it cannot be used in this situation.

Answer 1

From Enumerable.Cast()‘s remarks:

This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.

All of the LINQ operators will let you know if they are deferred execution or immediate query execution. Additionally, here are the standard LINQ operators which are NOT deferred:

• Aggregate
• All
• Any
• Average
• Contains
• Count
• ElementAt
• ElementAtOrDefault
• First
• FirstOrDefault
• Last
• LastOrDefault
• LongCount
• Max
• Min
• SequenceEqual
• Single
• SingleOrDefault
• Sum
• ToArray
• ToDictionary
• ToList
• ToLookup