query-syntax.md

LINQ Query Syntax

Click the run icon to get started. Try the following LINQ query:

The preceding query shows the major sections of a query: a source for the query, a series of transformations, and a projection that produces results. Following the query, the foreach loop consumes the data elements produced by the query. Let's look at each of these components in turn.

First, you have the data source:

from n in sequence

The from clause defines the the range variable, n, and specifies the the source, sequence. The source specifies the producer of all the elements processed in the query. The range variable defines a variable that holds each element of the source in turn as the query executes.

Next, you write any number of transformations:

where n % 2 == 1

Every transformation produces an output sequence from its input sequence. This transformation is a filter. The where keyword defines a filter. The code n % 2 == 1 is a lambda expression that defines the condition for elements that pass the filter. As you work through more lessons in this tutorial, you'll create more complicated transformations. These transformations use lambda expressions that can be more complicated expressions to define the behavior of the query. Another common transformation is to order the results. Add the following line between the where clause and the select clause:

orderby n descending

Click Run and the output sequence is in the reverse order.

Finally, every query ends with a projection:

select n * n;

Every query ends with a projection that produces either a new sequence, or a single value. This first example produces a sequence where every element is the square of the input sequence.

You can modify any of these sections in the query and run it yourself.

Next: Lazy evaluations » Previous: Home «