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The Essence of LINQ

This chapter covers the seven foundations on which an understanding of LINQ can be built.
This chapter is from the book

This chapter is from the book

Now that you’ve seen several practical examples of LINQ’s syntax, it is time to view the technology from a more theoretical perspective. This chapter covers the seven foundations on which an understanding of LINQ can be built. LINQ is

  • Integrated
  • Unitive
  • Extensible
  • Declarative
  • Hierarchical
  • Composable
  • Transformative

These ideas may sound esoteric at first, but I believe you will find them quite easy to understand. LINQ has a fundamental simplicity and elegance. In this chapter and the next, we explore LINQ’s architecture, giving you a chance to understand how it was built and why it was built that way. This chapter explains goals that LINQ aims to achieve. The next chapter explains each of the pieces of the LINQ architecture and shows how they come together to achieve those goals.


LINQ stands for Language Integrated Query. One of the central, and most important, features of LINQ is its integration of a flexible query syntax into the C# language.

Developers have many tools that have been crafted to neatly solve difficult tasks. Yet there are still dark corners in the development landscape. Querying data is one area in which developers frequently encounter problems with no clear resolution. LINQ aims to remove that uncertainty and to show a clearly defined path that is well-lit and easy to follow.

In Visual Studio 2005, attempts to query data in a SQL database from a C# program revealed an impedance mismatch between code and data. SQL is native to neither .NET nor C#. As a result, SQL code embedded in a C# program is neither type-checked nor IntelliSense-aware. From the perspective of a C# developer, SQL is shrouded in darkness.

Here is an example of one of several different techniques developers used in the past when querying data:

SqlConnection sqlConnection = new SqlConnection(connectString);
System.Data.SqlClient.SqlCommand sqlCommand = new SqlCommand();
sqlCommand.Connection = sqlConnection;
sqlCommand.CommandText = "Select * from Customer";
return sqlCommand.ExecuteReader(CommandBehavior.CloseConnection)

Of these six lines of code, only the last two directly define a query. The rest of the lines involve setup code that allows developers to connect and call objects in the database. The query string shown in the next-to-last line is neither type-checked nor IntelliSense-aware.

After these six lines of code execute, the developers may have more work to do, because the data returned from the query is not readily addressable by an object-oriented programmer. You might have to write more lines of code to access this data, or convert it into a format that is easier to use.

The LINQ version of this same query is shorter, easier to read, color-coded, fully type-checked, and IntelliSense-aware. The result set is cleanly converted into a well-defined object-oriented format:

Northwind db = new Northwind(@"C:\Data\Northwnd.mdf");

var query = from c in db.Customers
            select c;

By fully integrating the syntax for querying data into .NET languages such as C# and VB, LINQ resolves a problem that has long plagued the development world. Queries become first-class citizens of our primary languages; they are both type-checked and supported by the powerful IntelliSense technology provided inside the Visual Studio IDE. LINQ brings the experience of writing queries into the well-lit world of the 21st century.

A few benefits accrue automatically as a result of integrating querying into the C# language:

  • The syntax highlighting and IntelliSense support allow you to get more work done in less time. The Visual Studio editor automatically shows you the tables in your database, the correctly spelled names and types of your fields, and the operators you can use when querying data. This helps you save time and avoid careless mistakes.
  • LINQ code is shorter and cleaner than traditional techniques for querying data and, therefore, is much easier to maintain.
  • LINQ allows you to fully harness the power of your C# debugger while writing and maintaining queries. You can step through your queries and related code in your LINQ projects.

If language integration were the only feature that LINQ offered, that alone would have been a significant accomplishment. But we are only one-seventh of the way through our description of the foundations of LINQ. Many of the best and most important features are still to be covered.

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