Field Templates - ASP.NET Dynamic Data - page 107

Navigation Columns

So far, our discussion has been about the lookup rules Dynamic Data uses for columns of
primitive types that can be stored using built-in system types like Int32 and String . The
Dynamic Data metadata API represents them using the MetaColumn class.

Navigation columns, on the other hand, are columns that provide access to one or more
entities that are defined as custom classes in the data model itself. There are three types of
navigation columns from the Dynamic Data prospective:

. MetaForeignKeyColumn represents a navigation property that returns a single entity
referenced by the underlying foreign key field. In the Northwind example, Product is
a foreign key column of the Order_Detail entity that represents the Product entity
referenced by the ProductID foreign key field.

. MetaChildrenColumn is an opposite of a foreign key. In the Northwind example,
Order_Details column of the Product entity returns all Order_Detail items that
reference a particular product instance.

. Many-to-Many column is a special case of a MetaChildrenColumn where the
IsManyToMany property is set to true . In the Northwind example, the Territories
column of the Employees entity returns all territories assigned to a particular
employee. Likewise, the Employees column of the Territory entity returns all
employees assigned to work in a particular Territory. Dynamic Data considers both
of these columns as Many-to-Many.

Navigation columns get special treatment during field template lookup. Unless the devel-
oper already placed a UIHintAttribute on a navigation property, Dynamic Data uses the
rules shown in Table 3.3 to come up with a default UI Hint.

TABLE 3.3 Navigation Column Rules
Column Type

UI Hint

MetaForeignKeyColumn ForeignKey

MetaChildrenColumn Children

MetaChildrenColumn, IsManyToMany = true ManyToMany

In this example, it means that for the Product column of the Order_Details table, Dynamic
Data uses a template called ForeignKey.ascx ; for the Order_Details column of the Product
table, it uses a template called Children.ascx ; and for both Employee.Territories and
Territory.Employees columns, it uses the template called ManyToMany.ascx .

Effectively, there is no type fallback during template lookup for navigation columns.
However, Dynamic Data does perform mode fallback, so if your page needs a foreign key
template in Insert mode, it first tries ForeignKey_Insert.ascx , then ForeignKey_Edit.ascx ,
and then ForeignKey.ascx if necessary. The default Dynamic Data project template