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Chapter 19. LINQ > Deferred vs. Immediate Query Execution

Deferred vs. Immediate Query Execution

In LINQ, queries have two different modes of execution: immediate and deferred. As explained early in this chapter, a query defines a set of rules that are not actually executed until a foreach statement executes. This is called deferred execution.

However, if you use one of the extension methods that produces a non-sequence result, then the query must be executed to obtain that result. For example, consider the Count( ) method. In order for Count( ) to return the number of elements in the sequence, the query must be executed, and this is done automatically when Count( ) is called. In this case, immediate execution takes place, with the query being executed automatically in order to obtain the result. Therefore, even though you don’t explicitly use the query in a foreach loop, the query is still executed.


  

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