Sunday, December 16, 2007

Language Integrated Query (LINQ) in .NET Framework 3.5

With the addition of Language Integrated Query (LINQ) in .NET Framework 3.5, the process of building SQL queries using error-prone string manipulation is a thing of the past. LINQ makes your relational data queries a first-class language construct in C# and Visual Basic, complete with compiler and Intellisense support. For Web applications, the ASP.NET LinqDataSource control allows you to easily use LINQ to filter, order and group data that can then be bound to any of the data visualization controls like the ListView and GridView controls.

They can express efficient query behavior in their programming language of choice, optionally transform/shape data query results into whatever format they want, and then easily manipulate the results. LINQ-enabled languages can provide full type-safety and compile-time checking of query expressions, and development tools can provide full intellisense, debugging, and rich refactoring support when writing LINQ code.

There are various facilities within LINQ to address data-specific attributes of content. Among them is DLinq, which can be used to query relational data stores using the syntax and compilers of the existing programming languages. When querying against a relational store, DLinq translates the query from an expression tree into a SQL expression. DLinq will also be integrated into ADO.NET, a Microsoft tool for creating queries of relational data over Web-based networks.
Another key LINQ facility, XLinq, will play a similar role for querying all types of XML data. XML has historically been difficult for developers to work with. XLinq allows developers to combine XML queries and transformations with queries from other data sources.

The standard query operators allow queries to be applied to any IEnumerable-based information source.
Sample :C#
using System;
using System.Query;
using System.Collections.Generic;

class app {
static void Main() {
string[] names = { "Burke", "Connor", "Frank",
"Everett", "Albert", "George",
"Harris", "David" };

IEnumerable expr = from s in names
where s.Length == 5
orderby s
select s.ToUpper();

foreach (string item in expr)

The local variable expr is initialized with a query expression. A query expression operates on one or more information sources by applying one or more query operators from either the standard query operators or domain-specific operators.
This expression uses three of the standard query operators: Where, OrderBy, and Select.
The arguments to the Where, OrderBy, and Select operators are called lambda expressions, which are fragments of code much like delegates. They allow the standard query operators to be defined individually as methods and strung together using dot notation. Together, these methods form the basis for an extensible query language.

Retrieving data from Database
(I will cover this topic extensively in the next article )
C# (selecting products)
NorthWindDatacontext db=NorthWindDatacontext();
var products=from p in db.products
where p.category.categoryname='xyz'
select p;
this query will select all the products in the with categoryname 'xyz'
NorthWindDatacontext represents the Northwind database genarated by LINQ to SQL feature of Visual studio 2008
LINQ to SQL is an O/RM (object relational mapping) implementation that ships in the .NET Framework 3.5, and which allows you to model a relational database using .NET classes. You can then query the database using LINQ, as well as update/insert/delete data from it.
LINQ to SQL fully supports transactions, views, and stored procedures. It also provides an easy way to integrate data validation and business logic rules into your data model.
For the time being only this much, stay tuned for the next part.

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