.NET Tip: Where Is Your Data Coming From?

LINQ to Objects allows you to use LINQ queries with any object that support IEnumerable or IEnumerable(T). This means that you can use LINQ to acccess data in arrays, lists, dictionaries, and other collections. You also can use LINQ with any of your own classes that implement or inherit IEnumerable. Let me start with a very simple introduction using an array of integers. This following example uses LINQ to find all of the even integers in an array of integers:

// Array of data
int[] Data = { 17, 32, 51, 98, 87, 4, 63, 26, 75, 40 };

// Create the variable to store the query
var EvenNumbers = from Num in Data
                  where Num % 2 == 0
                  select Num;

// Run the query and output the results
foreach (int i in EvenNumbers)
   Debug.Print(i.ToString());

Data is simply an integer array. The only thing important about it is that arrays implement IEnumerable so LINQ can be used with them. The statement of interest in this example is the definition of EvenNumbers. The from clause is used to define a subset of the elements in Data. Num is called the range variable and is used to represent each element from the data source. The where clause is used here to include only those numbers that are evenly divisible by 2, eliminating all odd numbers. The select clause indicates what information about each Num should be included for each matching element. In this case, the number itself is being selected. One point to note is that at this point the query has not been executed. EvenNumbers is simply a definition of the query. The query is not actually processed until it is used in the foreach loop that follows. The piece is the foreach loop that iterates over the EvenNumbers query and prints out each included element. The result is the following:

32
98
4
26
40

I hope this whets your appetite for what LINQ can do and will help you to think about where you can use LINQ in your application. LINQ allows you to use a SQL-like syntax for working with your data outside of the database.

About the Author

Jay Miller is a Software Engineer with Electronic Tracking Systems, a company dedicated to robbery prevention, apprehension, and recovery based in Carrollton, Texas. Jay has been working with .NET since the release of the first beta and is co-author of Learn Microsoft Visual Basic.Net In a Weekend. Jay can be reached via email at jmiller@sm-ets.com.



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