Metadata API - ASP.NET Dynamic Data - page 201

Data Access Support
In addition to the metadata information, the MetaTable class also plays an important role
in implementing data access logic in Dynamic Data web applications:
public Type DataContextType { get; }
public string DataContextPropertyName { get; }
The DataContextType property of the MetaTable class returns a Type object that represents
the data context class generated by the data model. This class is typically derived from the
ObjectContext base class in Entity Framework and the DataContext class in LINQ to SQL.
The DataContextPropertyName property returns the name of the property you would use
to query the table rows, such as the Products property in the NorthwindEntities object
context. At run time, this information is used by the DynamicDataManager control in page
templates to configure the EntityDataSource and LinqDataSource controls responsible for
retrieving entity data and saving changes to the database.
NOTE
It is significant that DataContextType is a property of the MetaTable class and not
the MetaModel . A single MetaModel instance can have tables from different data
contexts registered by separate calls to the RegisterContext method. If different
contexts have the tables with the same name, your code needs to distinguish them by
passing the context type to the GetTable method of the MetaModel class, along with
the table name.
As you might recall from our discussion of the RegisterContext method of the MetaModel
class, if the object context requires additional initialization tasks, you can provide a
factory method when registering it, instead of simply giving it the type:
public virtual object CreateContext();
The CreateContext method of the MetaTable class is responsible for creating the context
object, either by creating an instance of the registered type or by calling the context
factory method, if that's how the context was registered with the MetaModel :
public IQueryable GetQuery();
public virtual IQueryable GetQuery(object context);
The MetaTable class also provides two overloaded GetQuery methods that can be used to
query any table dynamically. This is how the ForeignKey_Edit field template as well as the
ForeignKey filter template populate their drop-down list controls. These methods return a
LINQ IQueryable object that you can use to retrieve rows from the database. Chapter 14,
“Implementing Security,” discusses how the GetQuery method can be overridden to imple-
ment row-level security.