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| GStrv | classes | Read / Write / Construct Only |
| TrackerNotifierFlags | flags | Read / Write / Construct Only |
TrackerNotifier is an object that receives notifications about
changes to the Tracker database. A TrackerNotifier is created
through tracker_notifier_new(), passing the RDF types that are
relevant to the caller, and possible different TrackerNotifierFlags
to change TrackerNotifier behavior. After the notifier is created,
events can be listened for by connecting to the “events”
signal. This object was added in Tracker 1.12.
TrackerNotifier by default coalesces events so the user is only
notified of changes after all metadata is extracted and inserted
in the database, so the user is guaranteed that all relevant data
will be available at the time of notification. If this is not desired,
or when dealing with data not dealt with by tracker-extract, the
TRACKER_NOTIFIER_FLAG_NOTIFY_UNEXTRACTED flag can be passed.
If the TRACKER_NOTIFIER_FLAG_NOTIFY_UNEXTRACTED flag is passed,
created/updated elements may be notified in two steps, first a
CREATED/UPDATED event will be emitted, and then a second UPDATED
event might appear after further metadata is extracted.
TrackerNotifier is tracker:id centric, the ID can be
obtained from every event through tracker_notifier_event_get_id().
The expected way to retrieving metadata is a query of the form:
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SELECT ?urn … WHERE { ?urn a rdfs:Resource . … FILTER (tracker:id(?urn) = …) } |
If the flags TRACKER_NOTIFIER_FLAG_QUERY_URN or
TRACKER_NOTIFIER_FLAG_QUERY_LOCATION are passed, the extra metadata
will be available through tracker_notifier_event_get_urn() and/or
tracker_notifier_event_get_location(). Note that this metadata can't
be obtained for every element and situation, most notably during
TRACKER_NOTIFIER_EVENT_DELETE events.
If a resource is deleted, the TRACKER_NOTIFIER_EVENT_DELETE event
emitted will have a NULL location, even if the notifier was created
with the TRACKER_NOTIFIER_FLAG_QUERY_LOCATION flag enabled. At the
time of notifying, the resource does not exist anymore, so no
meatadata can be retrieved.
Notifications of files being moved across indexed folders will
appear as TRACKER_NOTIFIER_EVENT_UPDATE events, containing
the new location (if requested). The older location is no longer
known to Tracker, this may make tracking of elements in specific
folders hard using solely the TrackerNotifier/Tracker data
available at event notification time.
The recommendation to fix those is making the caller aware of tracker:ids, querying those in the application SPARQL queries so the client can search the formerly queried data for matching IDs when TrackerNotifier events happen. URNs are just as effective as a matching mechanism, but more costly.
TrackerNotifier * tracker_notifier_new (const gchar * const *classes,TrackerNotifierFlags flags,GCancellable *cancellable,GError **error);
Creates a new notifier, events can be listened through the TrackerNotifier::events signal.
classes |
Array of RDF classes to
receive notifications from, or |
[array zero-terminated=1][allow-none] |
flags |
flags affecting the notifier behavior |
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cancellable |
Cancellable for the operation |
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error |
location for the possible resulting error. |
Since: 1.12
TrackerNotifierEventType
tracker_notifier_event_get_event_type (TrackerNotifierEvent *event);
Returns the event type.
Since: 1.12
gint64
tracker_notifier_event_get_id (TrackerNotifierEvent *event);
Returns the tracker:id of the element being notified upon.
Since: 1.12
const gchar *
tracker_notifier_event_get_type (TrackerNotifierEvent *event);
Returns the RDF type that this notification event relates to, in their expanded forms (for example, http://www.semanticdesktop.org/ontologies/2007/03/22/nfoAudio).
A resource may have multiple RDF types. In the case of changes to a resource with multiple types, one event will be notified for each RDF type the notifier is subscribed to.
For performance reasons, Tracker only sends notifications for events that are explicitly marked with the tracker:notify property in their ontology.
Since: 1.12
const gchar *
tracker_notifier_event_get_urn (TrackerNotifierEvent *event);
Returns the Uniform Resource Name of the element if the
notifier has the flag TRACKER_NOTIFIER_FLAG_QUERY_URN enabled.
This URN is an unique string identifier for the resource being notified upon, typically of the form "urn:uuid:...".
Since: 1.12
const gchar *
tracker_notifier_event_get_location (TrackerNotifierEvent *event);
Returns the location (e.g. an URI) of the element if the notifier
has the flag TRACKER_NOTIFIER_FLAG_QUERY_LOCATION, and it can
be obtained at the time of emission.
Since: 1.12
Flags affecting TrackerNotifier behavior.
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No flags |
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Query URN of notified elements |
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Query location of notified elements |
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Added/updated Elements are notified in 2 steps (a CREATE/UPDATE event after the file is first known, and an UPDATE event after metadata is extracted). The default TrackerNotifier behavior coalesces those events in one. |
struct TrackerNotifierClass {
GObjectClass parent_class;
void (* events) (TrackerNotifier *notifier,
const GPtrArray *events);
/* <Private> */
gpointer padding[20];
};
“classes” property“classes” GStrv
RDF classes to listen notifications about.
Flags: Read / Write / Construct Only
“flags” property“flags” TrackerNotifierFlags
Flags affecting TrackerNotifier behavior.
Flags: Read / Write / Construct Only
“events” signalvoid user_function (TrackerNotifier *self, GPtrArray *events, gpointer user_data)
Notifies of changes in the Tracker database.
self |
The TrackerNotifier |
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events |
[element-type TrackerNotifierEvent] | |
user_data |
user data set when the signal handler was connected. |