Building Dynamic List Pages - ASP.NET Dynamic Data - page 429

The overridden GetFilteredColumns method calls the GetScaffoldColumns method of the
MetaTable to get a list of all properties that can be displayed in a list page in read-only mode.
In other words, only columns already displayed in a dynamic GridView control are candi-
dates for filtering. This eliminates some low-level properties, such as the generated primary
keys and primitive components of foreign keys that are not displayed in list pages by default.
From the end-user perspective, it would be strange to see an option to filter a Product page
by the ProductID or the SupplierID columns, which are not displayed in the grid.
The initial list of properties returned by the GetScaffoldColumns method is further
reduced by calling the IsFilterable method and leaving only those MetaColumn objects
for which it returns true . This method mimics the rules used by the GetScaffoldColumns
method itself, only as they apply to filtering of property values, not their display. For
instance, if the property has a FilterUIHintAttribute applied to it, assume that it is
filterable. Likewise, if the property has a DisplayAttribute applied with an explicitly spec-
ified AutoGenerateFilter value, this value determines whether the property is considered
filterable ( true or false ). All other types of properties, with the exception of custom prop-
erties and “children” navigation properties, are considered filterable by default.
Extending the MetaModel Class
The MetaModel class serves as a root object for accessing the metadata information in
Dynamic Data web applications. Its default implementation creates and exposes the built-
in FilterFactory and MetaTable classes. The UnleashedMetaModel extends the built-in
class to create the UnleashedFilterFactory and UnleashedMetaTable instances instead.
Listing 13.3 shows a complete implementation of the new class.
LISTING 13.3 Unleashed.DynamicData\UnleashedMetaModel.cs
using System;
using System.Web.DynamicData;
using System.Web.DynamicData.ModelProviders;
namespace Unleashed.DynamicData
{
public class UnleashedMetaModel : MetaModel
{
public UnleashedMetaModel()
{
this.FilterFactory = new UnleashedFilterFactory(this);
}
protected override MetaTable CreateTable(TableProvider provider)
{
return new UnleashedMetaTable(this, provider);
}
}
}