Relation notifications

[bjarnef]

Currently there a lot of different notifications to hook into.
https://our.umbraco.com/documentation/Reference/Notifications/

However there isn't any relation specific notifications, which I think would be useful when relations are created or deleted, e.g.

• RelationSavingNotification
• RelationSavedNotification
• RelationDeletingNotification
• RelationDeletedNotification

For example this could be use to "sync" a two pickers between Page A and B, where picker on Page A select page of type B, and picker on Page B select page of type A. In that way the property value could be updated when the relation change.

[bergmania]

Hey @bjarnef.

I agree, but to my knowledge these notifications already exists.. https://github.com/umbraco/Umbraco-CMS/blob/v11/contrib/src/Umbraco.Core/Services/RelationService.cs

So the question is, if it is "just" missing documentation :) ?

[bjarnef]

@bergmania yes, it looks like some missing documentation like ContentCacheRefresherNotification isn't documented either.
umbraco/UmbracoDocs#4536

I will try these. Besides that I noticed the UmbracoEntityReference didn't work as expected with a custom relation type as it doesn't removed previous relations, so it tries to insert new records which already exists. Currently it only works with umbDocument and umbMedia defined in AutomaticRelationTypes constant.
#13364

[bjarnef]

@bergmania I tried with RelationDeletingNotification but if check for deleted reference and update the property on the other one (the one picked) it seems I would get an infinite loop, because it always remove the relations first, before the new ones is created. Not sure if it could only remove relations which are removed, e.g. if A, B and C is picked and C is removed... it seems to remove all and create A and B relations again.
#13364 (comment)

[bjarnef]

Am I correct that RelationDeletingNotification and RelationDeletedNotification notifications are triggered for all items in picker, e.g. A, B and C.

Umbraco-CMS/src/Umbraco.Infrastructure/Persistence/Repositories/Implement/ContentRepositoryBase.cs

Lines 1045 to 1046 in b69afe8

	// First delete all auto-relations for this entity
	RelationRepository.DeleteByParent(entity.Id, Constants.Conventions.RelationTypes.AutomaticRelationTypes);

and afterwards the new references are saved based on implementation of UmbracoEntityReference in GetReferences():

Umbraco-CMS/src/Umbraco.Infrastructure/Persistence/Repositories/Implement/ContentRepositoryBase.cs

Lines 1064 to 1085 in b69afe8

	IEnumerable<ReadOnlyRelation> toSave = trackedRelations.Select(rel =>
	{
	if (allRelationTypes is null || !allRelationTypes.TryGetValue(rel.RelationTypeAlias, out IRelationType? relationType))
	{
	throw new InvalidOperationException($"The relation type {rel.RelationTypeAlias} does not exist");
	}
	if (!udiToGuids.TryGetValue(rel.Udi, out Guid guid))
	{
	return null; // This shouldn't happen!
	}
	if (!keyToIds.TryGetValue(guid, out var id))
	{
	return null; // This shouldn't happen!
	}
	return new ReadOnlyRelation(entity.Id, id, relationType.Id);
	}).WhereNotNull();
	// Save bulk relations
	RelationRepository.SaveBulk(toSave);

I think it would be useful it only triggered a notification for the ones deleted/removed. In my use-case I have a picker on a Category node to select courses, e.g. Course 1, Course 2 and Course 3.

Even I only remove Course 2, all three are triggering the RelationDeletedNotification.
So if I wants to "sync" a reference in a Category picker on the Course nodes, it would also remove this Category from Course 1 and Course 3 even though only Course 2 was was removed from the Category. I could of course handle the RelationSavingNotification or RelationSavedNotification to update the values on Course 1 and 3, but it would make on unnecessary save of Course 1 and 3, when only Course 2 is the one expected to update (since this was removed from the course picker on the category).