Databases Reference
In-Depth Information
Perhaps the reason why the lookup algorithm for filter templates is so simplistic compared
to field templates is that only three filter templates come with a Dynamic Data web
project by default.
Boolean
The
Boolean
filter template is used for columns of Boolean type. It contains a
DropDownList control that allows the user to choose filter value from
All
,
True
,
False
,
and
[Not Set]
if the column allows
null
values.
Enumeration
The
Enumeration
filter template is used for columns of enum types or integer columns
marked with the
EnumDataTypeAttribute
that specifies an enum type. It contains a
DropDownList
control that allows users to choose filter value from All,
[Not Set]
(if the column allows
null
values), as well as the string names of all items in the enumer-
ated type.
ForeignKey
The
ForeignKey
filter template is used for foreign key columns. It displays all records from
the parent table referenced by the foreign key column in a
DropDownList
control, plus
All
and
[Not Set]
(if the column allows
null
values). Each
ListItem
represents a single row
from the parent table. Its
Value
property contains a comma-separated list of primary key
column values. The
Text
property value is determined by calling the
GetDisplayString
method of the
MetaTable
instance describing the parent table. If the parent entity class
overrides the
ToString
method, the value returned by this method is used; otherwise, the
value of the display column of the parent entity class is used. Display column can be spec-
ified explicitly, by applying the
DisplayColumnAttribute
to the entity class, or determined
heuristically, in which case the value of the first string property is used.
Summary
A filter template is a special type of user control that encapsulates both user interface and
data access logic required to filter rows of a particular table based on the values of a single
column. Filter template modifies the LINQ query created by a data source control to apply
the filter criteria dynamically, based on the search parameter entered by the user. Multiple
instances of the same filter template can be used in an application for different columns
of the same type. Dynamic Data includes a small number of ready-to-use filter templates,
including templates for Boolean, enumeration, and foreign key columns. New filter
templates can be implemented using built-in or third-party ASP.NET controls and LINQ
expressions or dynamic LINQ extensions.
