Chapter 8. LINQ Queries
LINQ, or Language Integrated Query, is a set of language and framework features for writing structured type-safe queries over local object collections and remote data sources. LINQ was introduced in C# 3.0 and Framework 3.5.
LINQ enables you to query any collection implementing IEnumerable<T>, whether an array, list, or
XML DOM, as well as remote data sources, such as tables in SQL Server. LINQ
offers the benefits of both compile-time type checking and dynamic query
composition.
This chapter describes the LINQ architecture and the fundamentals of
writing queries. All core types are defined in the System.Linq and System.Linq.Expressions namespaces.
Note
The examples in this and the following two chapters are preloaded into an interactive querying tool called LINQPad. You can download LINQPad from http://www.linqpad.net.
Getting Started
The basic units of data in LINQ are sequences and
elements. A sequence is any object that implements
IEnumerable<T> and an element is
each item in the sequence. In the following example, names is a sequence, and "Tom", "Dick", and "Harry" are elements:
string[] names = { "Tom", "Dick", "Harry" };We call this a local sequence because it represents a local collection of objects in memory.
A query operator is a method that
transforms a sequence. A typical query operator accepts an input
sequence and emits a transformed output
sequence. In the Enumerable class in
System.Linq, there are around 40 query operators—all implemented as static ...
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