A Phased Approach for Converting SQL-centric Applications to LINQ

lmost all applications need to integrate some sort of data, often from multiple data sources such as SQL Server or Oracle database tables. In .NET languages, you would traditionally perform these operations using SQL or an SQL variant in conjunction with a data access technology such as ADO.NET. But when applications need to perform similar data operations against XML files, you would need to write code using the XML classes provided by the .NET Framework. While the intent—retrieving and updating data from a store—is the same in both cases, the knowledge and the code implementations required differ significantly for each data store.

In other words, until now, data access in the .NET framework has lacked a unified and consistent approach to accessing data from disparate data sources. To solve these data access inconsistencies, Microsoft introduced LINQ, the Language INtegrated Query Framework, which adds general-purpose query facilities for querying all types of information, including (but not limited to) relational and XML data. But as usual, technological advances present a quandary; although LINQ provides an excellent set of features for data access, you can't simply throw away your existing investments in ADO.NET and SQL in favor of LINQ. Instead, you need a seamless way to migrate existing SQL-centered applications to use LINQ. This article shows you how to take a phased approach to migrate a SQL-centered ASP.NET application to leverage the features of LINQ.