Menu
Data sources that implement the IEnumerable<T> generic interface can be queried through LINQ. Calling AsEnumerable on a DataTable returns an object which implements the generic IEnumerable<T> interface, which serves as the data source for LINQ to DataSet queries.
Can we use linq to query against a DataTable? Explanation: We cannot use query against the DataTable's Rows collection, since DataRowCollection doesn't implement IEnumerable<T>. We need to use the AsEnumerable() extension for DataTable.
To query datatable using linq we call the AsEnumerable() method of the DataTable. Calling this method on the DataTable returns an object which implements the IEnumerable<T> interface. Now we can perform LINQ queries on this object. Add a reference to the System.
LINQ to DataSet makes it easier and faster to query over data cached in a DataSet object. Specifically, LINQ to DataSet simplifies querying by enabling developers to write queries from the programming language itself, instead of by using a separate query language.
As mentioned in the question, IEnumerable has a CopyToDataTable method:
IEnumerable<DataRow> query =
from order in orders.AsEnumerable()
where order.Field<DateTime>("OrderDate") > new DateTime(2001, 8, 1)
select order;
// Create a table from the query.
DataTable boundTable = query.CopyToDataTable<DataRow>();
Why won't that work for you?
To perform this query against a DataContext class, you'll need to do the following:
MyDataContext db = new MyDataContext();
IEnumerable<DataRow> query =
(from order in db.Orders.AsEnumerable()
select new
{
order.Property,
order.Property2
})
as IEnumerable<DataRow>;
return query.CopyToDataTable<DataRow>();
Without the as IEnumerable<DataRow>; you will see the following compilation error:
Cannot implicitly convert type 'System.Collections.Generic.IEnumerable' to 'System.Collections.Generic.IEnumerable'. An explicit conversion exists (are you missing a cast?)
Make a set of Data Transfer Objects, a couple of mappers, and return that via the .asmx.
You should never expose the database objects directly, as a change in the procedure schema will propagate to the web service consumer without you noticing it.
If you use a return type of IEnumerable, you can return your query variable directly.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With