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== How to create a MoDisco query set ==
== How to create a MoDisco query set ==
The first step is to [[MoDisco/ProjectNature|create a
The first step is to [[MoDisco/ProjectNature|create a MoDisco project]].
MoDisco project]].
Then right-click on the MoDisco project and select '''New > Other ...'''.
Then right-click on the MoDisco project and select '''New > Other ...'''.

Revision as of 02:17, 6 May 2010

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How to create a MoDisco query set

The first step is to create a MoDisco project.

Then right-click on the MoDisco project and select New > Other ....

MoDisco Facet NewOther.png

Select QuerySet Model and press the Next button

MoDisco NewQuerySetWizard.png

Choose a name for your model query set (My.querySet in the example) and press Finish.

MoDisco NewQuerySetWizard Name.png

Open the "My.querySet" file and open the "Properties View"

Set the description of the query set and make sure that the query set name is the same as the containing file name ("My" in the example).

MoDisco QuerySetProperties.png

How to create a MoDisco query

The easy way

Right-click on a query set, and choose Create Query.

MoDisco CreateQueryAction.png

This opens the Create Query wizard, with the parent query set already selected.

Fill in the query name, description, scope and return type. Then click Finish.

MoDisco CreateQueryWizard.png

A Java editor opens on the Java class that was created for your query. Complete the "evaluate" method body with your code:

MoDisco JavaQueryClassCode.png

Then do File > Save in the query set editor.


The wizard does everything for you, but it is still interesting to know how to create and edit a query manually. Also, the wizard only handles creating Java queries for now, so if you want to create an OCL query for example, then you have to do it manually.

Load the resources containing the meta-models used by the model queries that will be owned by the query set. To load a meta-model resource use the Load meta-model resource action in the query set editor.

MoDisco Query LoadMetamodelResource.png

In this example, we choose to use the KDM meta-model.

MoDisco Query Package Selection KDM.png

Fill the "Associated Metamodels" field with the ePackages containing the meta-models used by the model queries that will be owned by the query set.

MoDisco Query Properties AssociatedMetamodels.png

In this example we use the "core" package.

MoDisco Query Associated Metamodels Core.png

Right click on the ModelQuerySet element and choose the New Child > Java Model Query action to create a "Java Model Query".

MoDisco Query NewChild JavaModelQuery.png

Set the name, the description and the return type of the query. Set the "Implementation Class Name" field with the qualified name of the class that will contain the query's Java implementation.

MoDisco Query JavaModelQuery Properties.png

Fill the "Scope" field with the meta-class to which the query will be applicable.

MoDisco QueryScope.png

MoDisco QueryScopeKDMEntity.png

MoDisco PropertiesScopeKDMEntity.png

A MoDisco project is also a "Plug-in project". To be able to refer to the API of the used meta-model, we have to add the "org.eclipse.gmt.modisco.infra.query.core" plug-in and the meta-model implementation plug-in to the plug-in dependencies.

MoDisco QueryPluginDependencies.png

Create the query's implementation class.

MoDisco NewJavaQueryClass.png

The Java Query implementation class must implement

MoDisco NewJavaQueryClassWizard.png

MoDisco JavaQueryClassCode.png

How to consult the MoDisco query set catalog through the UI

If a query set model is valid, it is registered in the model query set catalog. To consult the model query set catalog, we can use the "Model Query Set" view.

To get this view select Windows > Show view > Other ... in the menu bar and choose "Query Sets" in the list.

MoDisco Window ShowView Other.png

MoDisco ShowView QuerySets.png

The "Query Sets" view presents the available query sets and their queries. And for each query, its description and model location are displayed.

MoDisco QuerySetsView.png

How to programmatically use the MoDisco query set catalog

Here a MoDisco query API example is provided. For more information please refer to the JavaDoc.

import org.eclipse.emf.ecore.EObject;
import org.eclipse.gmt.modisco.infra.query.ModelQuery;
import org.eclipse.gmt.modisco.infra.query.ModelQuerySet;
import org.eclipse.gmt.modisco.infra.query.core.AbstractModelQuery;
import org.eclipse.gmt.modisco.infra.query.core.ModelQuerySetCatalog;
import org.eclipse.gmt.modisco.infra.query.runtime.ModelQueryResult;
public class Example {
  public Integer main(EObject context) throws Exception {
    // Get the model query set catalog.
    ModelQuerySetCatalog catalog = ModelQuerySetCatalog.getSingleton(); 
    // Get the query set named "My".
    ModelQuerySet modelQuerySet = catalog.getModelQuerySet("My");
    // Select in the "My" query set a query named "myQuery".
    // modelQueryDescription is a model element.
    ModelQuery modelQueryDescription = null;
    for (ModelQuery modelQuery : modelQuerySet.getQueries()) {
      if (modelQuery.getName().equals("myQuery")) {
        modelQueryDescription = modelQuery;
    if (modelQueryDescription == null) {
      throw new Exception();
    //Get a java instance of the querySet
    AbstractModelQuery myModelQuery = catalog
    //the model query set evaluation
    ModelQueryResult result = myModelQuery.evaluate(context);
    if (result.getException() != null) {
      throw new Exception();
    return (Integer) result.getValue();

How to package a query set in a plug-in

To package a query set in a plug-in, an extension must be added in the file plugin.xml (contained in the query set's project). The extension point to use is: org.eclipse.gmt.modisco.infra.query.registration. Here is an example of a query set declaration:


Thanks to this extension declaration, The MoDisco project is ready to be exported as a plug-in.

Query Meta-model Description

MoDisco Query Metamodel.png

ModelQuerySet is the root of the query model. One root per query model is expected.

ModelQuerySet::name must be unique (in the Eclipse platform) and equal to the containing file name. We recommend to use a name prefix with a namespace, for example: org.eclipse.gmt.modisco.example1.querySet1.

ModelQuerySet::isEditable is true if the query can be edited. If the query is stored into a compiled file then ModelQuerySet::isEditable is false.

ModelQuerySet::getQuery(EString) returns the contained ModelQuery having the requested name.

ModelQuerySet::associatedMetamodels points to the meta-models used by the contained queries.

ModelQuerySet::queries refers to the contained queries.

ModelQuery is an abstract class representing a query.

ModelQuery::name is the query name. In each query set the query names must be unique.

ModelQuery::parameters a set of ModelQueryParameter instances describing the query parameters.

ModelQuery::returnType is an ecore::DataType representing the query return type.

ModelQuery::scope is the set of types on which the query is applicable. Those types are represented by ecore::DataType instances.

ModelQueryParameter is a class representing the query parameters.

ModelQueryParameter::type is an ecore::DataType representing the query parameter type.

ModelQueryParameter::name is the parameter name. In each query the parameter names must be unique.

ModelQuery::isExternalContextDependent must be true if two evaluations of the same query with the same context and parameters can return different results.

JavaModelQuery is a sub class of ModelQuery which points to a Java implemented query.

JavaModelQuery::implemenationClassName contains the qualified name of the class implementing the query. This class must be a sub class of The Java implementation class must be stored in the same plug-in (or plug-in project) as the query model.

OCLModelQuery::query is the OCL query string.

JXPath Queries

JXPath Meta-model Extension Description

JXPath Query Meta-model Extension

A JXPathModelQuery is a ModelQuery describing a JXPath expression.

The JXPath expressions are stored into the JXPathModelQuery::query attribure.


The jxpathQueryTest.querySet model provides an example of a JXPath query. The JXPathQuery stored into jxpathQueryTest.querySet returns the name of the EPackage passed in the query context.

How to log in a Java query

If you want to log errors or messages in a Java query, you can use the MoDisco logger, like this (where Activator is the class that is already generated by default in your MoDisco project):

  • To log an error message:
MoDiscoLogger.logError("Error message", Activator.getDefault());
  • To log an exception:
MoDiscoLogger.logError(exception, Activator.getDefault());
  • To log an information message:
MoDiscoLogger.logInfo("Error message", Activator.getDefault());
  • ... (see also the other methods on MoDiscoLogger)

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