Databases Reference
In-Depth Information
var query = from s in context.Suppliers
select
new { s.CompanyName, s.City };
foreach (var item in query)
Console.WriteLine(item.CompanyName + “ “ + item.City );
An anonymous type is declared in-place, with property names inferred from the names of
the Supplier properties that provide the values. It serves as a Data Transfer Object (DTO)
that holds Supplier property values in place of the actual Supplier instances. This particu-
lar code could be also rewritten to use an explicitly defined DTO class, like so:
class SupplierProjection
{
public string CompanyName;
public string City;
}
var query = from s in context.Suppliers
select new SupplierProjection
{
CompanyName = s.CompanyName,
City = s.City
};
As you can see, the version based on the anonymous type is much more concise and
closely resembles the SQL syntax. However, visibility of anonymous types is limited to the
methods where they are defined. You need to declare the projection classes explicitly if
you need to pass the DTOs to another function for further processing.
NOTE
Projection objects are not entity instances. They do not participate in the identity
management process of the
ObjectContext
and cannot be used to change the under-
lying database records.
Sorting
The
orderby
LINQ keyword can be used to sort query results. Here is how you could sort
the list of Products in the order of
UnitPrice
, from highest to lowest:
var query = from p in context.Products
orderby
p.UnitPrice
descending
select p;
By default,
orderby
acts like its counterpart in SQL: Sorting is performed in ascending
order. To reverse the sort order for a property, use the
descending
LINQ keyword after the
