Designing the data model: How to extend a data class to higher layers
Is there a better explanation of this topic, "How to extend a data class to higher layers", than the one found in the LSA course? Specifically, applying the template pattern to Dynamic Class Referencing. The template pattern is not explained in reference to DCR. There is an example but it does not explain clearly how the D_Vehicle data page can be configured to use polymorphism. The example also shows .pxObjClass being set in the AddToVehicleList data transform but that causes a severe best practice warning. Other sites claim that we should simply turn off this warning. Where is the DCR in this example? I thought DCR required using a class reference page at the enterprise level that can be overridden at the implementation level. This example hints that DCR can be done without the reference page by just using inheritance and perhaps manipulating .pxObjClass but I am not clear from reading what Pega's recommended approach is. Finally, can we mix vehicle types in the list? Can the list be implemented at the enterprise level so that a single instance of a list can support a mix cars, trucks and motorcycles at the same time?
Pegasystems Inc.
US
The figures in the LSA course unfortunately do not show the timeline of what takes place when.
Imagine you are looking at a screen that display an Org-Data-Vehicle data instance. That instance can be an embedded page or an editable Data Page.
There are two options:
- When the .Type property is set, immediately post the value and refresh the screen
- Require the .Type property to be set, but do not immediately react to it being set.
Next an “Add to List” button is clicked.
The attached diagram demonstrates (1). The figures in the LSA course demonstrate (2).
The figures in the LSA course assume that the pxObjClass of the current/Primary Page has yet to be modified prior to AddVehicleToList being called.
AddVehicleToList declaratively asks a Data Page for the class. Ideally that Data Page would be named “D_VehicleDCR” not “D_Vehicle”.
D_VehicleDCR asks its load Data Transform to set the value of a .Class property based on the value of a Type parameter.
The AutoQuote application layer overrides that load Data Transform setting .Class to a value that begins with Org-App-Data as opposed to Org-Data-.
The current/Primary Page then sets it pxObjClass to D_VehicleDCR[Type:Primary.Type].Class.
The rest is simply appending the Primary page to a Work- .VehicleList PageList property.
The figures in the LSA course unfortunately do not show the timeline of what takes place when.
Imagine you are looking at a screen that display an Org-Data-Vehicle data instance. That instance can be an embedded page or an editable Data Page.
There are two options:
- When the .Type property is set, immediately post the value and refresh the screen
- Require the .Type property to be set, but do not immediately react to it being set.
Next an “Add to List” button is clicked.
The attached diagram demonstrates (1). The figures in the LSA course demonstrate (2).
The figures in the LSA course assume that the pxObjClass of the current/Primary Page has yet to be modified prior to AddVehicleToList being called.
AddVehicleToList declaratively asks a Data Page for the class. Ideally that Data Page would be named “D_VehicleDCR” not “D_Vehicle”.
D_VehicleDCR asks its load Data Transform to set the value of a .Class property based on the value of a Type parameter.
The AutoQuote application layer overrides that load Data Transform setting .Class to a value that begins with Org-App-Data as opposed to Org-Data-.
The current/Primary Page then sets it pxObjClass to D_VehicleDCR[Type:Primary.Type].Class.
The rest is simply appending the Primary page to a Work- .VehicleList PageList property.
Regarding the Template Pattern, AddVehicleToList itself could be overridden at the application, for example to initiate a credit check in the background.
Pegasystems Inc.
US
Finally, can we mix vehicle types in the list? << YES.
Can the list be implemented at the enterprise level so that a single instance of a list can support a mix cars, trucks and motorcycles at the same time? << YES
Care must be taken when persisting data to the CustomerData schema where Pega-specific columns such as pzInsKey and pxObjClass do not exist. The DCR process described above needs to be revisited when a data instance is retrieved; the Type property providing the necessary input.
Also note that constructing an object and setting its class using Page-New is not the same as changing a class dynamically after the instance is constructed. The difference is that Page-New supports invoking the pyDefault Data Transform.
It is possible to defect when a particular class has yet to be initialized, at that point initializing it once and for all.
Also note that application layer classes directly extend enterprise layer classes whereas enterprise layer classes whereas enterprise classes directly extend the same class that they pattern-inherit.
Finally, can we mix vehicle types in the list? << YES.
Can the list be implemented at the enterprise level so that a single instance of a list can support a mix cars, trucks and motorcycles at the same time? << YES
Care must be taken when persisting data to the CustomerData schema where Pega-specific columns such as pzInsKey and pxObjClass do not exist. The DCR process described above needs to be revisited when a data instance is retrieved; the Type property providing the necessary input.
Also note that constructing an object and setting its class using Page-New is not the same as changing a class dynamically after the instance is constructed. The difference is that Page-New supports invoking the pyDefault Data Transform.
It is possible to defect when a particular class has yet to be initialized, at that point initializing it once and for all.
Also note that application layer classes directly extend enterprise layer classes whereas enterprise layer classes whereas enterprise classes directly extend the same class that they pattern-inherit.
If initialization is needed at the application layer for the pattern-inherited class, you must invoke a data transform with a different name than pyDefault plus do so before the application layer's class-specific pyDefault transform steps are invoked.
LTIMindtree
GB
Template Design Pattern is nothing but creating an abstract/complete template of common features and extending as per type to make it more specific-
Ex: Creating a HouseType is a template where common feature will go to give it a skeleton
Org-Data-House
Roof , Floor, windows, doors , pillars,
Making it more specific in application layer
Org-App-Data-House-Wooden extends from Org-Data-House
Roof- wooden
Floor-Wooden
Doors-Wooden
Pillars-Wooden
---------------------------------------------------------------
Org-App-Data-House-Glass extends from Org-Data-House
Roof- Glass
Floor-Tiles
Doors-Glass
Pillars-Concrete
in the above example the template house being extended to satisfy specific needs in app layers