Developing Model-to-Text Transformations - Eclipse Modeling Project: A Domain-Specific Language Toolkit - page 283

M2M from a source model into a Java model, followed by Java generation using
dedicated templates. The alternative is to pass the source model to a set of tem-
plates designed to output Java code. In the former, the logical mapping from one
model to the other takes place in the mappings of QVT; in the latter, the logic
resides in Xpand and Xtend code throughout the templates and extension files.
Sometimes one approach is superior to the other; as with the two following
examples, both are feasible when transforming our Domain-Neutral Component
(DNC) models to Java Persistence API (JPA) code.
BEST PRACTICE
This might seen obvious, but it's typically easier to first write code that
works and templify it than to try to work in a template environment from
the beginning.This applies to all text output formats, not just Java.
7.3.1 Using Java Model and Dedicated Template
In this section, we develop the template used to generate Java code from our Java
EMF Model (JEM) instance. We use a single template, which you can see in its
entirety next, followed by the Xtend utilities used by the template.
The Main definition takes a collection of JavaPackage elements. As you
can see in the corresponding workflow file used to invoke the template, the
source model can contain multiple root elements, which explains the use of
Collection . The package definition is invoked for each JavaPackage , which
expands each JavaClass that is not marked with a “ library ” annotation.
Subpackages are then processed recursively. The jemUtil.ext file contains the
functions used throughout to construct fully qualified class, package, and path
strings.
« IMPORT java»
« EXTENSION templates::java::jemUtil»
« DEFINE Main FOR Collection[java::JavaPackage]»
« EXPAND package FOREACH this .typeSelect(JavaPackage)»
« ENDDEFINE »
« DEFINE package FOR java::JavaPackage-»
« EXPAND class FOREACH javaClasses.select(c |
c.eAnnotations.first().source != 'library')»
« EXPAND package FOREACH eSubpackages.typeSelect(JavaPackage)»
« ENDDEFINE »