Using JET Transformations with EMF Documents
By default, JET transformations expect an XML document as
input. However, JET transformations can be modified to load EMF-based
models, too. This section describes how to load EMF documents
with JET and how JET accesses the models.
Loading EMF Documents
To enable a JET Transformation to load an EMF document, the transformation's plugin.xml
must be modified.
Do the following:
- Open the plugin.xml file in the root of the JET
transformation project.
- Click on the Extensions tab.
- Expand the org.eclipse.jet.transform element in
the All Extensions tree. This will reveal the
(transform) child element.
- Click on the (transform) element.
- In the modelLoader
field, enter
org.eclipse.jet.emf .
XPath expressions against EMF documents
The JET XPath processor handles EMF documents by mapping the document's
meta-model to the XPath infoset model as follows:
-
Resource objects map to the infoset ;root object.
The XPath expression
/ refers to the Resource
containing the input model.
- The Resource contents, as returned by the
getContents() method, maps to an element
contents. The XPath expression
/contents
returns the results of this method.
- Each
EReference feature on an object is mapped to an element with
the same name.
If
$class refers to an EObject with an EReference ownedAttributes, then
$class/ownedAttributes will return all the elements in that collection.
- Each
EAttribute feature on an object is mapped to an attribute
with the same name.
If
$class refers to an EObject with an EAttribute name, then
$class/@name will return the value of this attribute.
- When evaluating XPath child-axis expressions, JET will first
attempt to identify an feature with the requested name. If no
feature is found, then the contained children of the element are
searched for instances of an EClass with the specified name.
For example, if the
$class refers to an EObject that contains instances of an EClass Property
in any of its reference features, the $class/Property will return those objects.
Example: XPath expressions against .ecore files
If a JET transform loads an ECore model (a .ecore file), then the following
XPath expressions would return the following results:
| XPath expression |
Java equivalent |
/contents
|
Resource.getContents()
|
/EPackage
|
the subset of Resource.getContents() of type
EPackage
|
$ePackage/eClassifiers (ePackage is an
EPackage instance) |
ePackage.getEClassifiers()
|
$ePackage/EClass
|
the subset of ePackage.eContents() of type
EClass
|
$ePackage/@name
|
ePackage.getName()
|
Accessing XPath Variables from Java code
JET templates may contain Java code, and this Java code may
access XPath variables. This is particularly valuable when the
input model is EMF-based. The following examples handles
hypothetical ECORE model loaded by a JET transform, and accesses
the model with both XPath and Java expressions
<%-- contents of main.jet that reads handles a .ecore file --%>
<%-- import the ecore namespace, needed for Java expressions --%>
<%@jet imports="org.eclipse.emf.ecore.*"%>
<c:setVariable var="ePackage" select="/contents"/>
<%-- write to the JET execution console --%>
<c:log>
EPackage: <c:get select="$ePackage/@name"/>
<c:iterate select="$ePackage/eClassifiers" var="eClassifier">
<%
EClassifier ec = (EClassifier)context.getVariable("eClassifier");
%>
EClassifier: <c:get select="$eClassifier/@name"/>. Really it's <%= ec.getName() %>
</c:iterate>
</c:log>
Details of EMF Document loading
JET uses the EMF method ResourceSetImpl.createResource()
to create a Resource implementation capable of loading themode.
This requires the model's EPackage is registered with EMF in order to load model
instances.
The Model loader id for EMF document loading is
org.eclipse.jet.emf.
Loading EMF documents during transformation execution
The launch framework automatically handles the loading of EMF resources passed to a JET
Transformation as input. If required, JET templates can load other EMF-based documents
during execution.
The
<c:load> and
<c:loadContent> tags may be used for this purpose.
The former loads a document from
an file, while the second loads the document by parsing the content of the c:loadContent tag.
The following loads the mymodel.ecore file that is part of the transformation plug-in:
<c:load url="mymodel.ecore"
loader="org.eclipse.jet.emf"
var="myEcore"/>
The following example loads the file mymodel.ecore from a workspace
project myproject.
<c:load url="myproject/mymodel.ecore"
urlContext="workspace"
loader="org.eclipse.jet.emf"
var="myEcore"/>
Finally, while it is possible to load ecore models with
<c:loadContent>, the format of Ecore models often makes
this impractical to embed a document within a JET template.
