How to update a TypeURI in a migration?

I am working on the biblio plugin that declares types. How can I write a migration to change the type URI of a previously existing topic type?
I found the setTypeUri method on the API documentation, but I’m obviously using it the wrong way. Any help is greatly appreciated! Here is what I tried:

package systems.dmx.biblio.migrations;

import systems.dmx.core.TopicType;
import systems.dmx.core.model.CompDefModel;
import systems.dmx.core.service.Migration;

public class Migration3 extends Migration {
    public void run() {
        TopicType type = dmx.getTopicType("dmx.biblio.monograph");

This migration fails with the following error:

Caused by: java.lang.RuntimeException: Topic 9839 is not associated to a topic type
    at systems.dmx.core.impl.TopicModelImpl.fetchInstantiation(
    at systems.dmx.core.impl.TopicModelImpl.reassignInstantiation(
    at systems.dmx.core.impl.TopicModelImpl.storeTypeUri(
    at systems.dmx.core.impl.DMXObjectModelImpl.updateTypeUri(
    at systems.dmx.core.impl.DMXObjectImpl.setTypeUri(
    at systems.dmx.core.impl.MigrationManager._runMigration(
    at systems.dmx.core.impl.MigrationManager.runMigration(
    ... 25 more

Little update: I found an example of a typeURI modification here. When I do it like that, the migration runs without errors, but I cannot reload the topicmap. It contains an instance of the type in question and now it seems to load forever. The only errors in the log file concern a missing favicon.

setTypeUri() is for retyping things. In Migration3 you’re using setTypeUri() on a type. You’re retyping a type. The topic with URI dmx.biblio.monograph is no longer a type. (It it now a Book instance.) The former Monograph instances become corrupt. This causes the RuntimeException.

You want change a type’s URI. For changing a thing’s URI there is setUri(). However using setUri() on a type is a tricky thing. More work is required in case instances of that type do exist. You can do this work in a Migration. Tell me if you need more info.

But actually you would expect the DMX Core to better support changing a type’s URI. Consider opening a ticket.

Excellent question!

1 Like
 * Renames data type "Identity" -> "Entity".
 * Part of DMX 5.0
 * Runs only on UPDATE
public class Migration4 extends Migration {

    public void run() {
        Topic identity = dmx.getTopicByUri("dmx.core.identity");
        identity.setSimpleValue(new SimpleValue("Entity"));

Here an instance URI is changed, not a type URI.
“Entity” is an instance (of type “Data Type”), not a type.

I don’t think there is a straight example for changing a type URI in existing (DM4/DMX) code. Tell me if you need more info for doing so.

General hint: usually the URI of a thing does not change. The URI identifies the thing. Usually a different URI identifies a different thing. Changing a thing’s URI is an exceptional case, and can create corrupt state when the former URI is still in use by other entities.

Good idea to support this in DMX core at some point. Yes, I will open a ticket for this.