Data View Delegates: Customization of a Data View

The platform provides a way to alter or extend the data views defined in a graph.

Tip: A data view is a PXSelect BQL expression declared in a graph for accessing and manipulating data. A data view may contain a delegate, which is an optional graph method that executes when the data view is requested. Every data view is represented by the PXView object and placed in the Views collection of the appropriate graph. To construct an instance of the PXView class, you use a PXSelect BQL expression and an optional delegate from the highest-level extension discovered.

Suppose that you have declared the Objects data view within the base graph, as shown below.

public class BaseGraph : PXGraph<BaseGraph, DAC>
{
    public PXSelect<DAC> Objects;
}

You can alter a data view within a graph extension in the following ways.

By Altering the Data View Within a Graph Extension

A data view that is redeclared within a graph extension replaces the base data view in the Views collection of the graph instance. Consider the following example of a first-level graph extension.

public class BaseGraphExt : PXGraphExtension<BaseGraph>
{
    public PXSelectOrderBy<DAC, 
               OrderBy<Asc<DAC.field>>> Objects;
}

The Views collection of a graph instance contains the PXView object, which uses the Objects data view declared within the first-level extension, instead of the data view declared within the base graph.

Attention: A data view redeclared within a graph extension completely replaces the base data view within the Views collection of a graph instance, including all attributes attached to the data view declared within the base graph. You can either attach the same set of attributes to the data view or completely redeclare the attributes.

By Declaring or Altering the Data View Delegate in a Graph Extension

The new delegate is attached to the corresponding data view. Consider the following example of a second-level graph extension.

public class BaseGraphExtOnExt : PXGraphExtension<BaseGraphExt, BaseGraph>
{
    protected IEnumerable objects()
    {
        return PXSelect<DAC>.Select(Base);
    }
}

The Views collection of a graph instance contains the PXView object, which uses the Objects data view declared within the first-level extension, with the objects() delegate declared within the second-level extension (see the diagram below).

Figure 1. The interaction among the levels of a graph extension

To query a data view declared within the base graph or a lower-level extension from the data view delegate, you should redeclare the data view within a graph extension. You do not need to redeclare a data member when it is not meant to be used from the data view delegate. Consider the following example of a second-level graph extension.

public class BaseGraphExtOnExt : PXGraphExtension<BaseGraphExt, BaseGraph>
{
    protected IEnumerable objects()
    {
        return Base.Objects.Select();
    }
}

The new delegate queries the data view declared within the base graph. Having redeclared the data view within the first-level extension, you prevent the data view execution from an infinite loop (see the following diagram).

Figure 2. The view of the base graph from the second-level delegate

Attention: If a data view declared within the base graph contains a delegate, this delegate also gets invoked when the data view is queried from the new delegate (see the following diagram).

Figure 3. The view with the delegate of the base BLC from the second-level delegate