C# 5.0 Programmer's Reference

Appendix J LINQ

This appendix provides syntax summaries for the most useful LINQ methods. For more detailed information, see Chapter 8, “LINQ.”

Basic LINQ Query Syntax

The following text shows the typical syntax for a LINQ query.

from ... where ... orderby ... select ...

The following sections describe these four standard clauses. The sections after those describe some of the other most useful LINQ clauses.

from

The from clause tells where the data comes from and defines the name by which it is known within the LINQ query.

from queryVariable in dataSource

Examples:

var customerQuery =
    from person in customers
    select person;
var scoresQuery =
    from student in students
    from score in testScores
    where student.StudentId == score.StudentId
    select new {student, score};

Usually, if you select data from multiple sources, you will want to use a where clause to join the results from the sources.

where

The where clause applies filters to the records selected by the from clause. The syntax follows.

where conditions

Use comparison operators (>, <, and ==), logical operators (!, |, and &&), object methods (ToString and Length), and functions to build complex conditions.

For example, the following query selects student and test score data, matching students to their test scores.

var scoresQuery =
    from student in students
    from score in testScores
    where student.StudentId == score.StudentId
    select new {student, score};

The following example selects students with last names starting with S.

var scoresQuery ...