Databases Reference
In-Depth Information
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The
EntityDataSource
control is used to retrieve the required entity instance from the
database. However, as you probably noticed, it does not specify the
DefaultContainerName
and the
EntitySetName
properties normally required for the control to know which
ObjectContext
to instantiate and which object set to query. This information is supplied
to the
EntityDataSource
by the
DynamicDataManager
, one of the new controls provided by
Dynamic Data.
The
DynamicDataManager
control has a
DataControls
collection that stores one or
more
DataControlReference
objects. In the Details page template, it stores a single refer-
ence to the
FormView
control. During the initialization phase of the page lifecycle, the
DynamicDataManager
uses this reference to find the
EntityDataSource
control associated
with the
FormView
and configures it. In particular, it extracts the table name from the
current URL route and obtains the
MetaTable
object describing the table. The
MetaTable
object provides the information necessary to initialize the
EntityDataSource
, including
the type of the
ObjectContext
as well as the name of the entity set to query.
Knowing the context type and the entity set is not enough to retrieve a specific entity
from the database. The query sent to the database server must also include a
WHERE
clause
that identifies the table row where it is stored. This task is performed by the
QueryExtender
control, which is associated with the
EntityDataSource
. In the Details
page template, the
QueryExtender
uses a special type of data source expression, called
DynamicRouteExpression
. At runtime, this object extracts the values of the primary key
columns from the URL and modifies the query generated by the
EntityDataSource
to
include appropriate filter criteria.
The
FormView
control defines an
ItemTemplate
to display the entity with the help of the
DynamicEntity
control. As you remember, this control uses Dynamic Data entity templates
to generate either a generic, single column view of the entity or a custom view if a custom
template was defined for the entity. In the Details page template, the
DynamicEntity
control does not specify the
Mode
property, so a
read-only
entity template is used.
In addition to the
DynamicEntity
, the
ItemTemplate
of the
FormView
control also includes
a set of links for users to edit or delete the entity or to go back to the List page. The Edit
and List actions are implemented by the
DynamicHyperLink
controls. When databound to
an entity instance, a
DynamicHyperLink
control generates a URL that points to another
dynamic page based on the value of the control's
Action
property. In this example, the
URL generated by the first
DynamicHyperLink
control looks like this:
http://localhost:49212/
Products/Edit.
aspx?
ProductID=1
In this URL,
Products
is the name of the
MetaTable
describing the current entity instance,
Edit
is the name of the action specified in the
Action
property of the
DynamicHyperLink
control, and
ProductID=1
is the name and value of the primary key column of the current
