C# in Depth

280 CHAPTER 11 Query expressions and LINQ to Objectsmakes the diagram a lot simpler. Just remember that each time the fetch occurs, it’seffectively checking for the end of the sequence as well. Figure 11.2 shows the first fewstages of our sample query expression in operation, when we print out each elementof the result using a foreach loop.As you can see in figure 11.2, only one element of data is processed at a time. If wedecided to stop printing output after writing “Holly,” we would never execute any ofthe operations on the other elements of the original sequence. Although severalstages are involved here, processing data in a streaming manner like this is efficient andCaller(foreach)Select Where Listfetchfetchfetchreturn {"Holly", 31}return {"Holly", 31}Check: Age >= 18? Yesreturn "Holly"Transform:{"Holly", 31} =>"Holly”Print "Holly"fetchfetchfetchreturn {"Tom", 4}Check: Age >= 18? Nofetchreturn {"Jon", 31}return {"Jon", 31}Check: Age >= 18? Yesreturn "Jon"Transform:{"Jon", 31} =>"Jon"Print "Jon"(and so on)Figure 11.2Sequence diagram of the execution of a query expressionLicensed to Rhona Hadida