LINQ to Typed DataSet

Database -> DataSet -> Typed DataSet -> ADO.NET Entity Framework -> LINQ.

Add a typed dataset by Main Menu -> Data -> Add Data Source.

    using NorthwindDataSetTableAdapters;

    NorthwindDataSet ds = new NorthwindDataSet();
    TableAdapterManager adapters = new TableAdapterManager();

    adapters.CustomersTableAdapter = new CustomersTableAdapter();
    adapters.OrdersTableAdapter = new OrdersTableAdapter();
    adapters.Order_DetailsTableAdapter = new Order_DetailsTableAdapter();
    adapters.ProductsTableAdapter = new ProductsTableAdapter();

    adapters.CustomersTableAdapter.Fill(ds.Customers);
    adapters.OrdersTableAdapter.Fill(ds.Orders);
    adapters.Order_DetailsTableAdapter.Fill(ds.Order_Details);
    adapters.ProductsTableAdapter.Fill(ds.Products);

    //Direct       
    Console.WriteLine("Direct-------------------------------------------");
    foreach (var row in ds.Customers)
        if (row.Country == "USA")
            Console.WriteLine(new { row.CustomerID, row.Country, row.ContactName });

    //LINQ to Object
    var query = ds.Customers
        .Where(c => c.Country == "USA")
        .Select(c => new { c.CustomerID, c.Country, c.ContactName });

    Console.WriteLine();
    Console.WriteLine("LINQ to Object------------------------------------");
    foreach (var row in query)
        Console.WriteLine(row);

    //LINQ to DataSet
    DataTable customersTable = (DataTable)ds.Customers;
    var query2 =
        from c in customersTable.AsEnumerable()
        where c.Field<string>("Country") == "USA"
        select c;

    Console.WriteLine();
    Console.WriteLine("LINQ to DataSet------------------------------------");
    foreach (var row in query2)
        Console.WriteLine(new
        {
            CustomerID = row.Field<string>("CustomerID"),
            Country = row.Field<string>("Country"),
            ContactName = row.Field<string>("ContactName")
        });

If you create the typed DataSet with Visual Studio, your typed DataTable classes will be derived from the TypedTableBase<T> class, which implements the IEnumerable<T> interface. For this reason, it is not required to call AsEnumerable to get a wrapper. 

    var query2 =
        //from c in customersTable.AsEnumerable()
        from c in ds.Customers
        where c.Field<string>("Country") == "USA"
        select c;

 

Reference

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MSDN: LINQ to DataSet
http://msdn.microsoft.com/en-us/library/bb386977.aspx