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Query typed DataSets

  • Статия

If the schema of the DataSet is known at application design time, we recommend that you use a typed DataSet when using LINQ to DataSet. A typed DataSet is a class that derives from a DataSet. As such, it inherits all the methods, events, and properties of a DataSet. Additionally, a typed DataSet provides strongly typed methods, events, and properties. This means that you can access tables and columns by name, instead of using collection-based methods. This makes queries simpler and more readable. For more information, see Typed DataSets.

LINQ to DataSet also supports querying over a typed DataSet. With a typed DataSet, you do not have to use the generic Field method or SetField method to access column data. Property names are available at compile time because the type information is included in the DataSet. LINQ to DataSet provides access to column values as the correct type, so that type mismatch errors are caught when the code is compiled instead of at run time.

Before you can begin querying a typed DataSet, you must generate the class by using the DataSet Designer in Visual Studio. For more information, see Create and configure DataSets.

Example

The following example shows a query over a typed DataSet:

var query = from o in orders
            where o.OnlineOrderFlag == true
            select new { o.SalesOrderID,
                         o.OrderDate,
                         o.SalesOrderNumber };

foreach(var order in query)
{
    Console.WriteLine("{0}\t{1:d}\t{2}",
      order.SalesOrderID,
      order.OrderDate,
      order.SalesOrderNumber);
}

Dim orders = ds.Tables("SalesOrderHeader")

Dim query = _
       From o In orders _
       Where o.OnlineOrderFlag = True _
       Select New {SalesOrderID := o.SalesOrderID, _
                   OrderDate := o.OrderDate, _
                   SalesOrderNumber := o.SalesOrderNumber}

For Each Dim onlineOrder In query
 Console.WriteLine("{0}\t{1:d}\t{2}", _
 onlineOrder.SalesOrderID, _
 onlineOrder.OrderDate, _
 onlineOrder.SalesOrderNumber)
Next

See also