PersistenceQuery
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Defined in: src/persistence/query/PersistenceQuery.ts:32
Read-side query layer for the journal. Designed for projections — processes that materialise a read-model by sweeping events out of the write-side journal and feeding them into a user handler.
Two flavours of query:
current*— one-shot snapshot of events currently in the journal at call time. Resolves to a Promise. Use this for a batch backfill or a self-contained report.events*— continuous live stream. Polls the journal atpollIntervalMsfor new events. Yields anAsyncIterableso consumers canfor await (const ev of stream) .... The stream stays open until the consumer breaks out of the loop or callsreturn()on the iterator.
Delivery guarantees: at-least-once. A projection that fails mid-event must accept that the event will be redelivered after restart. Handlers therefore have to be idempotent.
Push where the journal can push (#42). A live query subscribes
to journal.events when the journal exposes one, and polls at
pollIntervalMs when it does not. So an in-process journal
delivers within a tick while a cross-process one (Cassandra,
Postgres) — where an in-process bus could not see another node’s
writes anyway — keeps the polling loop. Which of the two is in
play is invisible to the consumer: the iteration contract is the
same either way.
Methods
Section titled “Methods”allPersistenceIds()
Section titled “allPersistenceIds()”allPersistenceIds(
options?):AsyncIterable<string>
Defined in: src/persistence/query/PersistenceQuery.ts:139
Live stream of every persistence id the journal has ever seen, plus
each new one as it first appears. The stream never completes on
its own — break out of the loop or call return() on the iterator.
This is the fan-out primitive: start a per-entity projection as its
entity shows up, instead of polling currentPersistenceIds and
diffing the result yourself.
Once per stream, not once per journal. A fresh subscription re-emits every id, so a consumer that must not act twice across a restart needs its own checkpoint — the same at-least-once posture the event queries have.
Memory. “Once per stream” is enforced with an in-process set of the ids emitted so far, so a stream over a journal with a million ids holds a million strings for as long as it runs. A lexicographic watermark would be cheaper and wrong: ids are not created in sorted order, so an id that sorts below the mark would be skipped forever, and a fan-out projection that silently never starts is the worst failure this API could have. The catch-up sweep is paged, so the peak is the set plus one page — and a one-shot enumeration that needs no set at all is currentPersistenceIdsPaginated.
Parameters
Section titled “Parameters”options?
Section titled “options?”Returns
Section titled “Returns”AsyncIterable<string>
currentEventsByPersistenceId()
Section titled “currentEventsByPersistenceId()”currentEventsByPersistenceId<
E>(persistenceId,fromSeq,toSeq?):Promise<PersistentEvent<E>[]>
Defined in: src/persistence/query/PersistenceQuery.ts:51
One-shot read of every event for persistenceId whose
sequenceNr >= fromSeq (and <= toSeq if given). Resolves
once with the events known at call time.
Type Parameters
Section titled “Type Parameters”E
Parameters
Section titled “Parameters”persistenceId
Section titled “persistenceId”string
fromSeq
Section titled “fromSeq”number
toSeq?
Section titled “toSeq?”number
Returns
Section titled “Returns”Promise<PersistentEvent<E>[]>
currentEventsByTag()
Section titled “currentEventsByTag()”currentEventsByTag<
E>(filter,fromOffset):Promise<TaggedEvent<E>[]>
Defined in: src/persistence/query/PersistenceQuery.ts:78
One-shot read of every event matching filter whose offset is
>= fromOffset. See TagFilter for the operator semantics.
Type Parameters
Section titled “Type Parameters”E
Parameters
Section titled “Parameters”filter
Section titled “filter”fromOffset
Section titled “fromOffset”Returns
Section titled “Returns”Promise<TaggedEvent<E>[]>
currentPersistenceIds()
Section titled “currentPersistenceIds()”currentPersistenceIds():
Promise<string[]>
Defined in: src/persistence/query/PersistenceQuery.ts:95
Snapshot of every persistence id known to the journal, as one array. Resolves once.
Kept, and not deprecated: for a journal with a handful of ids this is simply the convenient shape, and “small journal” is a permanent case rather than a legacy one. It is, however, the only method here with no bound on what it materialises — at a million ids that is a million strings in one allocation. Past the point where the array itself is a cost, use currentPersistenceIdsPaginated, which walks the same data one page at a time.
Returns
Section titled “Returns”Promise<string[]>
currentPersistenceIdsPaginated()
Section titled “currentPersistenceIdsPaginated()”currentPersistenceIdsPaginated(
options?):AsyncIterable<string>
Defined in: src/persistence/query/PersistenceQuery.ts:112
Cursor-paginated snapshot of the persistence ids currently in the
journal, ascending, yielded one at a time. Fetches pageSize ids
per round-trip, so peak memory is one page rather than the whole
set. Completes when the journal is exhausted — unlike
allPersistenceIds it does not wait for new ids.
The cursor is a persistence id, not an opaque token. Resume a
partial walk by passing the last id you handled as
afterPersistenceId. Encoding it would have bought per-backend
freedom that no backend here needs — every one of them enumerates
ids through an index keyed on the id itself — at the price of a
checkpoint no operator can read and no other process can
construct.
Parameters
Section titled “Parameters”options?
Section titled “options?”Returns
Section titled “Returns”AsyncIterable<string>
eventsByPersistenceId()
Section titled “eventsByPersistenceId()”eventsByPersistenceId<
E>(persistenceId,fromSeq,options?):AsyncIterable<PersistentEvent<E>>
Defined in: src/persistence/query/PersistenceQuery.ts:40
Live stream of every event for persistenceId whose
sequenceNr >= fromSeq. Past events are emitted first
(chronological by sequenceNr), then new events as they are
appended. The stream never completes on its own — break out of
the loop or call return() on the iterator to stop polling.
Type Parameters
Section titled “Type Parameters”E
Parameters
Section titled “Parameters”persistenceId
Section titled “persistenceId”string
fromSeq
Section titled “fromSeq”number
options?
Section titled “options?”Returns
Section titled “Returns”AsyncIterable<PersistentEvent<E>>
eventsByTag()
Section titled “eventsByTag()”eventsByTag<
E>(filter,fromOffset,options?):AsyncIterable<TaggedEvent<E>>
Defined in: src/persistence/query/PersistenceQuery.ts:68
Live stream of every event matching filter whose offset is
>= fromOffset. Yields events ordered by (timestamp, persistenceId, sequenceNr). See Offset for offset
semantics — the stream emits the offset alongside the event so
the consumer can persist progress.
filter accepts either a single tag string (back-compat shortcut
for { all: [tag] }) or a TagFilter object that combines
all (intersect), any (union), and not (exclusion) operators.
Type Parameters
Section titled “Type Parameters”E
Parameters
Section titled “Parameters”filter
Section titled “filter”fromOffset
Section titled “fromOffset”options?
Section titled “options?”Returns
Section titled “Returns”AsyncIterable<TaggedEvent<E>>