Help with filterExpression method in notification filters

Help / Discuss
1

I’m creating global notification filter that filters hidden documents.

I created new component based on role org.xwiki.notifications.NotificationFilter as documented here

There inside filterEvent method i have this

    return event.getDocument().isHidden()
            ? FilterPolicy.FILTER : FilterPolicy.NO_EFFECT;

But Im struggling how do I rewrite this condition in filterExpression method

@Override
public ExpressionNode filterExpression(DocumentReference user,
        Collection<NotificationFilterPreference> filterPreferences,
        NotificationFilterType type, NotificationFormat format)
{
    // what comes here??
}

Any help greatly appreciated.

2

I don’t know this topic and can’t help you much but the way I’d approach it is to check for example code implementing NotificationFilter and see how they do it.

Screenshot 2020-12-11 at 13.04.53

3

Note that I agree that the javadoc is pretty bad:

    /**
     * Filtering expression to use when retrieving notifications.
     *
     * @param user the user interested in the notifications
     * @param filterPreferences the collection of all preferences to take into account
     * @param preference the notification preference associated with the filter
     * @return the updated query
     *
     * @since 9.7RC1
     */
    ExpressionNode filterExpression(DocumentReference user, Collection<NotificationFilterPreference> filterPreferences,
            NotificationPreference preference);

It says the updated query but it doesn’t explain where is the query? I don’t see any query being passed!

cc @gdelhumeau

4

I understand that filterEventExpression is just condition rewritten as an expression, for example
in existing SystemUserNotificationFilter (for filtering system events) the filterEvent is

{
    return event.getUser() != null && event.getUser().getLocalDocumentReference().equals(SYSTEM_USER)
            ? FilterPolicy.FILTER : FilterPolicy.NO_EFFECT;
}

and corresponding FilterExpression is

    {
        if (type == NotificationFilterType.EXCLUSIVE) {
            return value(EventProperty.USER).notEq(value(serializer.serialize(SYSTEM_USER)));
        }
        return null;
    }

I still have no clue how to rewrite condition in my first post.

5

what do you need to rewrite?

6

are you saying there are no code example that is not returning null?

7

I see for ex:

    @Override
    public ExpressionNode filterExpression(DocumentReference user,
        Collection<NotificationFilterPreference> filterPreferences, NotificationFilterType type,
        NotificationFormat format)
    {
        if (user != null && type == NotificationFilterType.EXCLUSIVE && format == this.format) {
            ForUserNode node = new ForUserNode(user, this.read, this.format);

            return this.not ? not(node) : node;
        }

        return null;
    }
8

or:

    @Override
    public ExpressionNode filterExpression(DocumentReference user,
            Collection<NotificationFilterPreference> filterPreferences,
            NotificationFilterType type, NotificationFormat format)
    {
        if (type == NotificationFilterType.EXCLUSIVE && format == this.format) {
            return not(
                    value(EventProperty.TYPE).eq(value(UPDATE_TYPE)).and(
                        not(value(EventProperty.DOCUMENT_VERSION).endsWith(value(VERSION_SCHEME)))
                    )
            );
        }
        return null;
    }

etc

9

I m struggling to rewrite event.getDocument().isHidden() as filterExpression

10

well it turned out that filterEvent method only was sufficient enough (no filterExpression necessary)

I set it like this

public FilterPolicy filterEvent(Event event, DocumentReference user,
        Collection<NotificationFilterPreference> filterPreferences, NotificationFormat format)
{
    return event.getHidden() ? FilterPolicy.FILTER : FilterPolicy.NO_EFFECT;
}

then compiled and my global hidden files filter works!