Tuesday, 6 September 2011

LINQ Query Expressions in C# 3.0


Language-Integrated Query (LINQ) is the name for a set of technologies based on the integration of query capabilities directly into the C# language (also in Visual Basic and potentially any other .NET language). With LINQ, a query is now a first-class language construct, just like classes, methods, events and so on.
For a developer who writes queries, the most visible "language-integrated" part of LINQ is the query expression. Query expressions are written in a declarative query syntax introduced in C# 3.0. By using query syntax, you can perform even complex filtering, ordering, and grouping operations on data sources with a minimum of code. You use the same basic query expression patterns to query and transform data in SQL databases, ADO.NET Datasets, XML documents and streams, and .NET collections.
The following example shows the complete query operation. The complete operation includes creating a data source, defining the query expression, and executing the query in a foreach statement.
class LINQQueryExpressions
{
    static void Main()
    {

        // Specify the data source.
        int[] scores = new int[] { 97, 92, 81, 60 };

        // Define the query expression.
        IEnumerable<int> scoreQuery =
            from score in scores
            where score > 80
            select score;

        // Execute the query.
        foreach (int i in scoreQuery)
        {
            Console.Write(i + " ");
        }           
    }
}
// Output: 97 92 81

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