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Exploring the Technical Essentials of SAP Commerce Cloud

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cleanFiles/bookmap_SAP_Commerce_Cloud_Essentials_for_Develope_en-US_learning-sap-com_lsc-prod.zip (MMCP-DROPZONE) - 2023-10-23T13:02:50.000Z

DTO Management

<div id="content"><p tabindex="0">Now that you understand the role of the Facade Layer in SAP Commerce Cloud, you might be wondering how to customize this layer to meet your project’s specific requirement.</p><p tabindex="0">To support the customization of the Facade Layer, you need to understand:</p><ol><li tabindex="0">How to customize the façade data objects so that they can be displayed appropriately on the frontend layer.</li><li tabindex="0">How to customize the data object conversion process before they reach the frontend layer.</li></ol><p tabindex="0">First things first: the data objects related to the facade layer are typically called Data Transfer Object, or DTO.</p><p tabindex="0">Let’s see how DTOs are managed within SAP Commerce Cloud.</p><div class="kalturaVideoLessonWrapper"><div id="1_xhugeqy0" data-testid="video" class="kalturaVideoLessonContainer"></div></div></div>

DTO Management 

We begin with some context. Our web page requests data on some movies we’re interested in from a controller,  which passes a list of movie IDs to the getMovieDetailData method on the Movie façade.  That façade delegates the work of fetching movie data to the Cinema service by calling its getFilms method.  In turn, the service invokes a Data Access Object to query the database, and receives a list of FilmModel objects, which it returns to the façade. According to the getMovieDetailData method’s signature, the controller can expect a list of MovieDetailData objects  containing the data the page needs,  extracted by the façade from the list of FilmModels.  The controller forwards them to the view  and the information they contain is displayed by the browser. The beans used to transfer data from the façade to the view  are commonly called Data Transfer Objects, or DTOs.  SAP Commerce has a way to generate these objects declaratively.  Let’s see how that works. In this example, imagine  that the MovieDetailData DTO has a single String property, title. Then assume we’re working in an extension called,  unimaginatively enough, extension1.  In that extension’s resources folder,  we create a file named extension1-beans.xml. There, we describe our DTO using xml. Our definition will become a Java class when we perform an ant all.  Under the top-level beans tag,  we define our desired bean by providing a fully qualified class name.  That tells ant to create a Java class with that name, using the package hierarchy.  The classpath location for generated beans is the same as models,  namely the platform/bootstrap/gensrc directory.  The contents of the Java source file are created by the ant process. It begins with a package statement, then the class definition.  Since the class is a Java Bean, it is serializable and has a no-argument constructor.  So far, so good. Our xml bean definition then indicates we need a property named title, of type String. That means ant will define a private data member named title, and the necessary getter and setter methods. Once the bean’s source file has been generated, ant compiles it,  placing the compiled class file under the platform/bootstrap/modelclasses directory. What happens when we add a second property?  Named genre, it’s an enumerated property. We’ll define the enumeration in a moment. Adding this property means the Java source file will contain a second data member and the required accessor methods. Now for the enumeration. We want Genre to have three valid values,  Comedy, Drama, or Action.  We can generate the enumeration in the same manner we did the Java Bean, but this time with an enum tag. The fully-qualified name is used to generate a Java source file  containing the appropriate package statement, and an enum declaration. The content of the enum tag may include a description.  It won’t affect the generated Java code, but helps explain why we decided to generate this enumeration. We then define three values, which are echoed in the Java code when we run ant. That’s all very nice,  but it’s when we start combining beans.xml files from multiple extensions that this bean generation process becomes interesting.  Here, our second extension’s beans.xml file defines the same enumeration,  but with the value Documentary.  When we run ant, the contents of both beans.xml files is combined  to generate the Java source file, which now shows four valid values for Genre. The same goes for our DTO.  The second extension provides a bean definition for MovieDetailData, which is combined by ant with the definition from extension1 to produce an updated MovieDetailData Java source file  that now includes a Date private data member, releaseDate,  and its related accessor methods. But the second extension can do more than add to the definition of an enumeration or bean. It can define a new bean that extends our existing DTO. Let’s call it DocumentaryDetailData, which adds a String property called subject. The bean definition provides the fully qualified class  and explains that it extends another class, namely MovieDetailData.  The ant process generates a new source file for the extending class.  And like it did for the first DTO,  ant will generate a member variable,  along with accessor methods for the subject property. The DTO generation process is used throughout SAP Commerce.  For example, the commercefacades-beans.xml file defines a DeliveryModeData DTO, which has the following properties.  The last one, PriceData, is also a DTO,  which in this case is also defined by commercefacades.  In turn, the PriceData bean references a third DTO,  PriceDataType, which might be defined in another extension.  And that brings us to the biggest benefit of SAP Commerce’s DTO generation paradigm. Every SAP Commerce installation consists of many extensions working together.  Each extension may require other extensions, meaning not only that it relies on them to function,  but may also override their configuration. For example, say extension2 requires extension1.  That means its configuration supersedes that of extension1.  In turn, extension1 requires couponfacades and may override its configuration.  This carries forward to many extensions, including  acceleratorfacades, commercefacades, and, eventually, the platform core extension. So what if we weren’t using generated DTO classes?  In that case, we’d probably follow the normal Java inheritance paradigm, and extension2 would define a ProductData class that extends the class defined in extension1.  That class, in turn, would extend the ProductData class in couponfacades,  and so on up the chain until we get to the ancestor of all ProductData classes,  defined in the commercefacades extension. Not only is this approach inelegant,  but what happens if we choose not to include couponfacades in our build? That leaves us with extension1’s ProductData extending a class that is no longer available, and our compilation fails.  We’d have to manually edit most DTOs to extend other DTOs that were part of our build. Overall, this is a terrible approach.  Which is why we don’t use it.  Instead, every extension may include an items.xml and beans.xml file. During the ant process,  every extension in our build may contribute one or both of these files  to the combined files used by ant to generate Model and DTO classes.  Not all DTOs are intended for display on a page,  but those that are will normally be defined in facade extensions. And should we decide not to include certain extensions in our build,  then their items and beans definitions simply don’t make it into the combined definitions,  and the Java classes ant generates from them  don’t include any fields from those extensions.  And nothing breaks!  We like this flexible approach so much, we used it for both item types and DTO beans. This concludes our look at DTO Management using the Bean Generation Process.

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