Learning C# 3.0

Summary

• Language Integrated Query (LINQ) is a new technology that allows you to query data sources from within your code, without needing to rely on specific data translation classes.

• LINQ uses the same syntax with traditional databases, but also other data sources such as XML files, and even with collections in your application.

• LINQ allows you to issue queries against collections in your code, returning a subset that’s easier to work with.

• A LINQ data source collection must implement IEnumerable, and the collection the query returns must as well.

• The range variable is used to define the parameters of the query. It can be any valid C# name, and C# will automatically infer its type based on the returned values.

• Once you have the enumerable collection of returned results, you can manipulate them as you would any generic collection.

• You can use anonymous types and the var keyword in your queries to have the compiler infer the types in the query, whether simple or complex.

• You can use lambda expressions in your queries to define a method for evaluating the stored data, and then project the results onto a variable.

• The join clause can unite the data from two different collections, but it has a special syntax, requiring the name of the collection to join with, the field you’re joining on in each collection, and the fields that should be in the return set.

• LINQ to SQL classes allows you to use the LINQ syntax to query a SQL database.

• You need to include a reference to the System.Data.Linq namespace ...