Databases Reference
In-Depth Information
new row,
ROWVERSION
columns for which the server generates incremental values with
every insert and update, as well as the computed columns defined at the database table
level.
Dynamic Data always chooses a read-only field template to display values of generated
columns, regardless of whether the entity itself is displayed in Insert or Edit mode.
public bool IsCustomProperty { get; }
The
IsCustomProperty
of the
MetaColumn
class returns
true
for properties defined by
developers in code as opposed to the normal properties defined in the data model itself.
Out of the box, custom properties cannot be used for sorting or filtering purposes. The
framework also cannot verify that they are persisted in the database correctly. Because of
these reasons, Dynamic Data makes a safe bet and does not create filter or field controls
for custom properties by default; although it is possible to change this behavior by apply-
ing
UIHintAttribute
and
FilterUIHintAttribute
to the property in code.
NOTE
As of .NET version 4.0, service pack 1, the Dynamic Data provider for Entity Framework
does not support custom properties, and you will not find
MetaColumn
objects describ-
ing them. This is why it is impossible to use custom properties as display columns. As
mentioned earlier, this problem can be solved by extending the metadata provider,
which is discussed in Chapter 13.
Data Annotations
A large number of the
MetaColumn
public interface is dedicated to data annotations—the
.NET attributes that can be applied by developers to the entity properties in code.
public AttributeCollection Attributes { get; }
All attributes applied to a particular entity property can be accessed through the
Attributes
property of the
MetaColumn
class. Similar to the
Attributes
property of the
MetaTable
class, this property also includes the built-in attributes from the
System.ComponentModel
and
System.ComponentModel.DataAnnotations
namespaces as
well as any custom attributes that you might have created in your application.
Although it is possible to get all data annotations directly through the Attributes collec-
tion, doing so would require scanning it repeatedly, which would quickly drain the
precious CPU resources of your web server. Instead, Dynamic Data class scans the attrib-
utes only once, when the
MetaColumn
object is created, and stores their values in fields of
the object for instantaneous access later.
Scaffolding Support
Several data annotations and
MetaColumn
properties play an important role in the scaffold-
ing process, where Dynamic Data determines whether a particular column needs to be
