Databases Reference
In-Depth Information
Is it possible to implement interaction between field templates in a dynamically generated
web page? Yes. In fact you already have all the tools you need. Is it a good idea? Most of
the time, it is not. When you discover that two or more data entry controls on a form
need to interact with each other, the best course of action is to create a custom entity or
page template, where implementing the interaction will be easier and more straightfor-
ward. Chapter 10, “Building Custom Forms,” discusses how to accomplish this task in
detail.
However, you might discover recurring patterns in your entity model, where different
properties need the same type of interaction. In Chapter 10, a custom entity template was
created for the Customer entity to help users enter address information by suggesting a list
of
regions
based on the name of the
country
they entered. In the Northwind sample model,
several other entities include address properties, including
Customer
,
Employee
,
Supplier
,
and
Order
. After implementing the same pattern several times for different entities, you
might decide that a single,
dynamic
implementation would be beneficial.
NOTE
Remember that falling into the trap of creating a dynamic solution where custom code
would be more appropriate is very common. Dynamic is not better than Custom. Don't
try to implement a dynamic solution based on just one or two instances of a particular
pattern. With such a small number of cases, you will not have a sufficient understand-
ing of the pattern and will not recoup the additional effort required to implement a
dynamic solution. Even such a common pattern as the
Region/Country
properties
could have been efficiently implemented with custom code, such as the generic
Address entity template discussed in Chapter 4.
The key to implementing field template interaction with metadata is to place the logic of
how
to interact in the field templates and storing the information of
who
to interact with
in the metadata. As an example, the
Region
field template created in Chapter 10 can be
modified to provide an auto-completion list for users based on the value in the
Country
field template. However, because the country property can have different names in differ-
ent entities—it is called
ShipCountry
in the Order entity—you do not want to hard-code it
in the Region field template itself. Instead, the
Country
property name can be specified as
a control parameter in the
UIHintAttribute
for the Reg
i
on property, as shown in this
code snippet:
[MetadataType(typeof(Metadata))]
partial class Employee
{
private abstract class Metadata
{
[UIHint(“Region”, “WebForms”,
“CountryField”, “Country”)]
public object Region { get; set; }
