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use exclusive fromSequenceNumber in eventsByTag, #22145

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* The reason is to have a consistent approach for Sequence and
  TimeBasedUUID, which are both intended as unique event identifiers.
* This means that you can use the offset that is returned in `EventEnvelope`
  as the `offset` parameter in a subsequent query.
This commit is contained in:
Patrik Nordwall 2017-01-16 11:13:45 +01:00
parent 4a9c753710
commit 8083c0bf4a
15 changed files with 101 additions and 34 deletions
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14
akka-docs/rst/java/code/docs/persistence/PersistenceQueryDocTest.java
View file

@ -101,6 +101,17 @@ public class PersistenceQueryDocTest {
TimeUnit.MILLISECONDS), TimeUnit.MILLISECONDS);
}
/**
* You can use `NoOffset` to retrieve all events with a given tag or retrieve a subset of all
* events by specifying a `Sequence` `offset`. The `offset` corresponds to an ordered sequence number for
* the specific tag. Note that the corresponding offset of each event is provided in the
* [[akka.persistence.query.EventEnvelope]], which makes it possible to resume the
* stream at a later point from a given offset.
*
* The `offset` is exclusive, i.e. the event with the exact same sequence number will not be included
* in the returned stream. This means that you can use the offset that is returned in `EventEnvelope`
* as the `offset` parameter in a subsequent query.
*/
@Override
public Source<EventEnvelope, NotUsed> eventsByTag(String tag, Offset offset) {
if(offset instanceof Sequence){
@ -108,7 +119,8 @@ public class PersistenceQueryDocTest {
final Props props = MyEventsByTagPublisher.props(tag, sequenceOffset.value(), refreshInterval);
return Source.<EventEnvelope>actorPublisher(props).
mapMaterializedValue(m -> NotUsed.getInstance());
}
} else if (offset == NoOffset.getInstance())
return eventsByTag(tag, Offset.sequence(0L)); //recursive
else
throw new IllegalArgumentException("MyJavadslReadJournal does not support " + offset.getClass().getName() + " offsets");
}

2
akka-docs/rst/java/code/docs/persistence/query/MyEventsByTagJavaPublisher.java
View file

@ -84,7 +84,7 @@ class MyEventsByTagJavaPublisher extends AbstractActorPublisher<EventEnvelope> {
private void query() {
if (buf.isEmpty()) {
final String query = "SELECT id, persistent_repr " +
"FROM journal WHERE tag = ? AND id >= ? " +
"FROM journal WHERE tag = ? AND id > ? " +
"ORDER BY id LIMIT ?";
try (PreparedStatement s = connection.prepareStatement(query)) {

12
akka-docs/rst/java/persistence-query-leveldb.rst
View file

@ -95,10 +95,14 @@ with the given ``tags``.
.. includecode:: code/docs/persistence/query/LeveldbPersistenceQueryDocTest.java#tagger
You can retrieve a subset of all events by specifying ``offset``, or use ``0L`` to retrieve all
events with a given tag. The ``offset`` corresponds to an ordered sequence number for the specific tag.
Note that the corresponding offset of each event is provided in the ``EventEnvelope``, which makes it possible
to resume the stream at a later point from a given offset.
You can use ``NoOffset`` to retrieve all events with a given tag or retrieve a subset of all
events by specifying a ``Sequence`` ``offset``. The ``offset`` corresponds to an ordered sequence number for
the specific tag. Note that the corresponding offset of each event is provided in the
``EventEnvelope``, which makes it possible to resume the stream at a later point from a given offset.
The ``offset`` is exclusive, i.e. the event with the exact same sequence number will not be included
in the returned stream. This means that you can use the offset that is returned in ``EventEnvelope``
as the ``offset`` parameter in a subsequent query.
In addition to the ``offset`` the ``EventEnvelope`` also provides ``persistenceId`` and ``sequenceNr``
for each event. The ``sequenceNr`` is the sequence number for the persistent actor with the