Generated code - Using the typed view classes, Adapter

Preface

LLBLGen Pro supports read-only lists based on a database view (Typed View) or a selection of entity fields from one or more entities with a relation (not m:n) (Typed List). Although both elements are different, they both will be generated as a typed DataTable, which is a variant of the typed DataSet concept included in Visual Studio.NET. A typed DataTable is a class which derives from the .NET DataTable and defines properties and a row class to access the individual fields in a typed fashion.

In this section the typed view classes are briefly discussed and their usage is illustrated using examples.

Instantiating and using a Typed View

As described in the concepts section of the Designer documentation a Typed View definition is a 1:1 mapping of a database view on an element in an LLBLGen Pro project. A typed view contains, for each database view column, a field with the same name or the name you gave it. When the typed view element is generated into code, it will end up as a class derived (indirectly) from DataTable, a typed DataTable to be exact, which is usable as a read-only list. You can limit the number of rows using standard LLBLGen Pro filtering techniques. These techniques use Predicate Expressions and relations included in a RelationPredicateBucket object. (See: Getting started with filtering).

Because the typed DataTable is derived from the .NET DataTable class, it can be used to create DataView objects. With DataView objects you can apply specify additional filtering, sorting, calculations etc. As an illustration, we'll include the view 'Invoices' from the Northwind database, and use the Typed View 'Invoices' for the code examples.
Instantiating and filling a Typed View
To create an instance of the 'Invoices' typed view and fill it with all the data in the view, the following code is sufficient:

// [C#]
InvoicesTypedView invoices = new InvoicesTypedView();
DataAccessAdapter adapter = new DataAccessAdapter();
adapter.FetchTypedView(invoices.GetFieldsInfo(), invoices);
' [VB.NET]
Dim invoices As New InvoicesTypedView()
Dim adapter As New DataAccessAdapter()
adapter.FetchTypedView(invoices.GetFieldsInfo(), invoices)

The rows will be added as they are received from the database provider; no sorting nor filtering will be applied. Furthermore, all rows in the view are read, which is probably not what you want. Let's filter on the rows, so the Fill() method will only return those rows with an OrderID larger than 11000, and do not filter out duplicate rows:

// [C#]
InvoicesTypedView invoices = new InvoicesTypedView();
DataAccessAdapter adapter = new DataAccessAdapter();
RelationPredicateBucket bucket = new RelationPredicateBucket();
bucket.PredicateExpression.Add(InvoicesFields.OrderId > 11000);
adapter.FetchTypedView(invoices.GetFieldsInfo(), invoices, bucket, true);
' [VB.NET]
Dim invoices As New InvoicesTypedView()
Dim adapter As New DataAccessAdapter()
Dim bucket As New RelationPredicateBucket()
bucket.PredicateExpression.Add(New FieldCompareValuePredicate(InvoicesFields.OrderId, Nothing, ComparisonOperator.GreaterThan, 11000))
adapter.FetchTypedView(invoices.GetFieldsInfo(), invoices, bucket, True)

The overloaded FetchTypedView() versions also accept one or more of these other parameters:

Specifying a filter will narrow down the number of rows to the ones matching the filter. The filter can be as complex as you want. See for filtering information and how to set up sorting clauses Getting started with filtering and Sorting.
Instantiating a TypedView mapped onto a Stored Procedure Resultset.

When you map a TypedView onto a resultset of a stored procedure, the fetch action of the typed view is slightly different. Instead of the normal FetchTypedView method as described above, a different overload of FetchTypedView is used, by passing in a call to the stored procedure the returning the resultset the TypedView is mapped on. In the following example, a TypedView is mapped onto the resultset of a stored procedure which returns the Customers for a given country. 

// [C#]
CustomersOnCountryTypedView customersTv = new CustomersOnCountryTypedView();
using(DataAccessAdapter adapter = new DataAccessAdapter())
{
	adapter.FetchTypedView(customersTv, RetrievalProcedures.GetQueryForCustomersOnCountryTypedView("USA"));
}
' [VB.NET]
Dim customersTv as New CustomersOnCountryTypedView()
Using adapter As New DataAccessAdapter()
	adapter.FetchTypedView(customersTv, RetrievalProcedures.GetQueryForCustomersOnCountryTypedView("USA"))
End Using
Reading a value from a filled Typed View
After we've filled the typed view object, we can use the values read. As said, Typed View and Typed List objects in the form of a typed DataTable are read-only, and therefore extremely handy for filling lists on the screen or website, but not usable for data manipulation. For modifying data you should use the entity classes/collection classes.
Below, we'll read a given value from row 0, the value for the Sales person. We assume the invoices object is filled with data using any of the previously mentioned ways to do so.

// [C#]
string salesPerson = invoices[0].Salesperson;
' [VB.NET]
Dim salesPerson As String = invoices(0).Salesperson

That's it. The '0' points to the row, and the row is 'typed', thus has named properties for the individual columns in the object; you can just read the value using a property.

Null values
Because the TypedView (and TypedList) classes are derived classes from DataTable, the underlying DataTable cells still contain System.DBNull.Value values if the field in the database is NULL. You can test for NULL by using the generated methods IsFieldNameNull(). When reading a field which value is System.DBNull.Value in code, like the example above, will result in the default value for the type of the field, as defined in the TypeDefaultValue class. Databinding will result in the usage of a DataView, as that's build into the DataTable, which will then return the System.DBNull.Value values and not the TypeDefaultValue values.
Limiting and sorting a typed view
When sorting the data in a typed view we're not actually sorting the data in the object, but sorting the data before it is read into the object. This is achieved by using a sort operator in the actual SQL query. To do this, you specify a set of SortClauses to the Fill() method. Below is an example sorting the invoices typed view on the field 'ExtendedPrice' in descending order. Sort clauses are easily created using the SortClause factory in the generated code. We pass the same filter as mentioned earlier and we assume the variable adapter still holds a reference to a DataAccessAdapter instance.

// [C#]
invoices.Clear();	// clear al current data
ISortExpression sorterInvoices = new SortExpression(InvoicesFields.ExtendedPrice | SortOperator.Descending);
adapter.FetchTypedView(invoices.GetFieldsInfo(), invoices, bucket, 0, sorter, true);
' [VB.NET]
invoices.Clear()	' clear al current data
Dim sorterInvoices As ISortExpression = New SortExpression( _
	New SortClause(InvoicesFields.ExtendedPrice, Nothing, SortOperator.Descending))
adapter.FetchTypedView(invoices.GetFieldsInfo(), invoices, bucket, 0, sorter, True)

The rows are now sorted on the ExtendedPrice field, in descending order.
LLBLGen Pro v3.0 documentation. ©2010 Solutions Design