step3_reflexive

The Kevoree Modeling Framework Tutorial

STEP 3 Reflexive (Meta) Model Manipulation

This step of the KMF tutorial will guide you through the reflexive manipulation of models. This tutorial demonstrates the ability to use KMF without the need for code generation. This can ease the development for highly dynamic environments. The reflexive usage of KMF has nearly no performance impact.

It's important to notice the change in the pom.xml file, there is no .mm file, and no KMF compiler plugin activated. This project uses plain Java with only one dependency to the KMF framework.

Reflexive Creation of Meta Models

Hereafter, we create reflexively the same meta model as the one used in the step 0 to 2. First of all, we create a meta model (same as the .mm file):

KMetaModel metaModel = new MetaModel("SmartCityMetaModel");

Then we add the two meta classes City and District.

KMetaClass metaClassCity = metaModel.addMetaClass("City");
KMetaClass metaClassDistrict = metaModel.addMetaClass("District");

For each meta class we add attributes. The meta types of attributes are defined in the enum KPrimitiveTypes:

metaClassCity.addAttribute("name", KPrimitiveTypes.STRING);
metaClassDistrict.addAttribute("name", KPrimitiveTypes.STRING);
metaClassDistrict.addAttribute("nbcitizen", KPrimitiveTypes.LONG);

Finally, we add the "districts" relationship to the meta class City using as target type the metaClassDistrict. The null parameter means that this relationship declares no opposite relation in the target type.

metaClassCity.addReference("districts", metaClassDistrict, null);

Reflexive Model Creation

From a meta model we can create a model instance using:

KModel model = metaModel.createModel(DataManagerBuilder.buildDefault());

From this we can connect:

model.connect(o -> {  });

In the connect closure, we can initiate objects, like a city, using the meta class name

KObject city = model.createByName("City", BASE_UNIVERSE, BASE_TIME);

or a district using directly the meta class

KObject district_1 = model.create(metaClassDistrict, BASE_UNIVERSE, BASE_TIME);

Additionally, we reflexively can set attribute values

district_1.setByName("name", "District_1");
district_1.setByName("nbcitizen", 10000);

or add an object to a relationship using a name:

city.addByName("districts", district_1);
city.addByName("districts", district_2);

To see the structure of this model, we can serialize it to the console:

model.universe(BASE_UNIVERSE).time(BASE_TIME).json().save(city, System.out::println);

Visit API

The visit API is available on any KObject. This API is composed by two methods visit and visitAttributes.

Using the visit method, one can pass through all children objects of the source of the visit:

city.visit(elem -> {
    System.out.println("Visiting..." + elem.toJSON());
    return KVisitResult.CONTINUE;
}, o1 -> System.out.println("End of the visit"));

This example shows the complete visit of a city, which ends with the call of the last closure to be informed that all objects have been visited. During the visit, users have the ability to stop the visit by returning VISIT_STOP instead of CONTINUE.

Similarly, the visitAttributes method allows to visit all attributes of an object, e.g.,:

city.visitAttributes((metaAttribute, value) -> {
    System.out.println("City attribute " + metaAttribute.metaName() + ", type=" + metaAttribute.attributeType().name() + "=" + value);
});

Lookup API

All KObjects have a unique UUID, during their lifecycle (immutable, regardless where the object is stored). This UUID can be used to quickly retrieve an object from a model. This is shown in the following code snippet:

long cityUUID = city.uuid();
System.out.println("City uuid=" + cityUUID);
model.lookup(BASE_UNIVERSE, BASE_TIME, cityUUID, new KCallback<KObject>() {
    @Override
    public void on(KObject resolvedObject) {
        System.out.println("Resolved=" + resolvedObject.toJSON());
    }
});