Alias Subdomain

This module (incode-module-alias) provides the ability to attach Alias objects to arbitrary domain entities, where "alias" means an alternative identifier for the entity. Most commonly this is the identifier within some external system (in DDD terms: in some other bounded context).

The identity of the external system itself is represented in two ways: first by the "alias type" (general ledger, document management system" etc), and also by an "application tenancy path". The latter is the same concept as exists within the Security SPI module, and generally represents a multi-tenancy environment, eg to distinguish different countries. Thus, an Alias is the combination of the app tenancy, an alias type, and the alias reference itself (a simple string).

For example, a Party entity might have a different identifier within a general ledger system for France say, and another identifier again in centrally-managed document management system.

There are no requirements for domain objects with aliases implement any interfaces. Instead, Alias is an abstract class; the consuming application provides a subclass of Alias and related classes to act as the "glue" between the Alias and the "aliased" domain object. In total about 50 lines of boilerplate are required, details below.

This module places no constraints on either the alias type nor on the format of the application tenancy path. The alias type is represented by the AliasType; to use the module the application must implement the mandatory AliasTypeRepository SPI service which identifies the available AliasTypes. Similarly, the available application tenancy paths are provided to the module by the mandatory ApplicationTenancyRepository SPI service. In both cases the list of alias types and application tenancy paths is per aliased domain object; not every aliased object will have an alias in every external system.

Domain Model

The following class diagram highlights the main concepts:

class diagram

(The colours used in the diagram are - approximately - from Object Modeling in Color).


The module’s functionality can be explored by running the quickstart with example usage using the

A home page is displayed when the app is run this way:

010 run fixture script

These "aliasable" demo objects have a (contributed) aliases collection, and we can also add new aliases using a (contributed) addAlias(…​) action:

040 add alias

The action requires the application tenancy of the alias (as returned from the ApplicationTenancyRepository SPI service) to be specified:

050 enter alias details

and also the alias type (as returned from the AliasTypeRepository SPI service) to be specified:

052 enter alias details

and finally the external alias reference itself must be specified also:

054 enter alias details

The aliases for the Alias domain object is added to:

060 alias added to collection

Each Alias can also be viewed:

070 view alias

How to configure/use


Update your classpath by adding this dependency in your dom project’s pom.xml:


Check for later releases by searching Maven Central Repo.

For instructions on how to use the latest -SNAPSHOT, see the contributors guide.


In the AppManifest, update its getModules() method, eg:

public List<Class<?>> getModules() {
    return Arrays.asList(

For each domain object…​

In order to be able to add/remove aliases to a domain object, you need to:

  • implement a subclass of Alias for the domain object’s type.

    This is the object that will be polymorphically attached to the "aliased" domain object; the subtype provides the type-safe association (a foreign key within the RDBMS).

  • implement the SubtypeProvider SPI interface:

    public interface SubtypeProvider {
        Class<? extends Alias> subtypeFor(Class<?> domainObject);

    This tells the module which subclass of Alias to use to attach to the "aliased" domain object. The SubtypeProviderAbstract adapter can be used to remove some boilerplate.

  • subclass T_addAlias, T_removeAlias and T_aliases (abstract) mixin classes for the domain object.

    These contribute the "aliases" collection and actions to add and remove Aliases.

Typically the SPI implementations and the mixin classes are nested static classes of the Alias subtype.

For example, in the demo app the DemoObject domain object can have aliases by virtue of the AliasForDemoObject subclass:

@javax.jdo.annotations.PersistenceCapable(identityType= IdentityType.DATASTORE, schema="incodeAliasDemo")
@javax.jdo.annotations.Inheritance(strategy = InheritanceStrategy.NEW_TABLE)
@DomainObject(objectType = "incodeAliasDemo.AliasForDemoObject")
public class AliasForDemoObject extends Alias {                                             (1)

    private DemoObject demoObject;
    @Column(allowsNull = "false", name = "demoObjectId")
    @Property(editing = Editing.DISABLED)
    public AliasDemoObject getDemoObject() {                                                (2)
        return demoObject;
    public void setDemoObject(final AliasDemoObject demoObject) {
        this.demoObject = demoObject;

    public Object getAliased() {                                                            (3)
        return getDemoObject();
    protected void setAliased(final Object aliased) {
        setDemoObject((AliasDemoObject) aliased);

    @DomainService(nature = NatureOfService.DOMAIN)
    public static class SubtypeProvider extends AliasRepository.SubtypeProviderAbstract {   (4)
        public LinkProvider() {
            super(DemoObject.class, AliasForDemoObject.class);

    public static class _aliases extends T_aliases<DemoObject> {                            (5)
        public _aliases(final AliasDemoObject aliased) {
    public static class _addAlias extends T_addAlias<DemoObject> {
        public _addAlias(final AliasObject aliased) {
    public static class _removeAlias extends T_removeAlias<DemoObject> {
        public _removeAlias(final DemoObject aliased) {
1 extend from Alias
2 the type-safe reference property to the "aliased" domain object (in this case DemoObject). In the RDBMS this will correspond to a regular foreign key with referential integrity constraints correctly applied.
3 implement the hook setAliased(…​) method to allow the type-safe reference property to the "aliased" (in this case DemoObject) to be set. Also implemented getAliased() similarly
4 implementation of the SubtypeProvider SPI domain service, telling the module which subclass of Alias to instantiate to attach to the "aliased" domain object
5 mixins for the collections and actions contributed to the "aliased" domain object

SPI services

There are two further mandatory SPI domain services that must be implemented:

  • First, the ApplicationTenancyRepository returns the application tenancy (path)s that are available to locate alias types for a given aliased:

    public interface ApplicationTenancyRepository {
        Collection<String> atPathsFor(final Object domainObjectToAlias);

    Note that this isn’t (necessarily) the same as the application tenancy path of the object being aliased; rather it is the list of the paths available (eg: countries/regions) for which there is an alias type (eg an external system) that may contain an alias (external system identifier).

  • Second, the AliasTypeRepository interface returns the available alias types for a given application tenancy path and aliased:

    public interface AliasTypeRepository {
        Collection<AliasType> aliasTypesFor(final Object aliased, final String atPath);

    where AliasType is defined as the interface:

    public interface AliasType {
        String getId();

    Typically AliasType will be implemented as an entity or perhaps a view model. The "id" is used as a column in the database tables, but in the UI the end-user sees the title of the object that implements the interface.

    The Apache Isis framework curently (as of v1.14.0) does not support enums implementing interfaces; the example app shows how a view model can be used as a work-around.

Note that there can be multiple implementations of either of these interfaces. This is to support the use case that different unrelated entities in the application may have aliases; each such aliased object can have its own supporting implementations of these SPI interfaces.

UI Concerns

The attached Alias objects are shown in two contexts: as a table of Alias objects for the "aliased" domain object, and then as the actual subtype when the alias object itself is shown (eg AliasForDemoObject in the demo app).

In the former case (as a table) the Alias will be rendered according to the Alias.layout.xml provided by the module. In the latter (as an object) the alias will be rendered according to the layout provided by the consuming app, offering full control of the layout. The layout provided in the demo app (ie AliasForDemoObject.layout.xml) is a good starting point.

The example AliasForDemoObject.layout.xml uses a little bit of custom CSS to adjust the right-hand column down a number of pixels. This resides in application.css: .alias-col {
    padding-top: 41px;

The module also allows the title, icon and CSS for Alias objects to be customised. By default the values for these are obtained using default subscribers, namely - Alias.TitleSubscriber, Alias.IconSubscriber and Alias.CssClassSubscriber. The consuming module can override these values simply by providing alternative implementations.

For example, the demo app has this demo implementation:

@DomainService(nature = NatureOfService.DOMAIN )
public class DemoUiSubscriber extends AbstractSubscriber {

    public void on(Alias.TitleUiEvent ev) {
        Alias alias = ev.getSource();
        if(isType(alias, AliasTypeDemoEnum.DOCUMENT_MANAGEMENT)) {
            ev.setTitle("DocMgmt [" + alias.getAliasTypeId() + "] " + alias.getReference());

    public void on(Alias.IconUiEvent ev) {
        Alias alias = ev.getSource();
        if(isType(alias, AliasTypeDemoEnum.DOCUMENT_MANAGEMENT)) {
        } else if (isType(alias, AliasTypeDemoEnum.GENERAL_LEDGER)) {

    public void on(Alias.CssClassUiEvent ev) {
        Alias alias = ev.getSource();
        ev.setCssClass("Alias" + alias.getAtPath().replace("/", "-"));

    private static boolean isType(final Alias alias, final AliasTypeDemoEnum aliasType) {
        return alias.getAliasTypeId().equals(aliasType.getId());

which returns a different title, icon and alias.

The custom png icons are picked up from org.incode.module.alias.dom.impl package (in this case, Alias-docMgmt.png and Alias-GL.png. The custom CSS is supplied in the application.css of the demo app:

tr.Alias-nl {
    color: blueviolet;
tr.Alias-uk {
    color: chocolate;

Other Services

The module provides one further domain service, namely AliasRepository. This can be used for finding the aliases attached to an "aliased" object.

Known issues

(As noted above), as of v1.14.0 the Apache Isis framework does not support enums implementing interfaces; the example app shows how a view model can be used as a work-around.


Maven can report modules dependencies using:

mvn dependency:list -o -pl modules/dom/alias/impl -D excludeTransitive=true

which, excluding the Apache Isis modules, returns no direct compile/runtime dependencies.

The module does use icons from icons8.