Changes from Durable State
A typical source for Projections is the change stored with DurableStateBehavior
DurableStateBehavior
in Apache Pekko Persistence. Durable state changes can be tagged and then consumed with the changes query.
Apache Pekko Projections has integration with changes
, which is described here.
Dependencies
To use the Durable State module of Apache Pekko Projections, add the following dependency in your project:
- sbt
libraryDependencies += "org.apache.pekko" %% "pekko-projection-durable-state" % "1.0.0"
- Maven
<properties> <scala.binary.version>2.13</scala.binary.version> </properties> <dependencies> <dependency> <groupId>org.apache.pekko</groupId> <artifactId>pekko-projection-durable-state_${scala.binary.version}</artifactId> <version>1.0.0</version> </dependency> </dependencies>
- Gradle
def versions = [ ScalaBinary: "2.13" ] dependencies { implementation "org.apache.pekko:pekko-projection-durable-state_${versions.ScalaBinary}:1.0.0" }
Apache Pekko Projections requires Pekko 1.0.2 or later, see Pekko version.
Project Info: Apache Pekko Projections Durable State | |
---|---|
Artifact | org.apache.pekko
pekko-projection-durable-state
1.0.0
|
JDK versions | OpenJDK 8 OpenJDK 11 OpenJDK 17 |
Scala versions | 3.3.3, 2.13.13, 2.12.19 |
JPMS module name | pekko.projection.durable-state |
License | |
API documentation | |
Forums | |
Release notes | GitHub releases |
Issues | GitHub issues |
Sources | https://github.com/apache/pekko-projection |
Transitive dependencies
The table below shows the pekko-projection-durable-state
direct dependencies.The second tab shows all libraries it depends on transitively.
SourceProvider for changesByTag
A SourceProvider
SourceProvider
defines the source of the envelopes that the Projection
will process. A SourceProvider
for the changes
query can be defined with the DurableStateStoreProvider
DurableStateStoreProvider
like this:
- Scala
-
source
import org.apache.pekko import pekko.persistence.jdbc.state.scaladsl.JdbcDurableStateStore import pekko.persistence.query.DurableStateChange import pekko.persistence.query.Offset import pekko.projection.state.scaladsl.DurableStateSourceProvider import pekko.projection.scaladsl.SourceProvider val sourceProvider: SourceProvider[Offset, DurableStateChange[AccountEntity.Account]] = DurableStateSourceProvider .changesByTag[AccountEntity.Account](system, JdbcDurableStateStore.Identifier, "bank-accounts-1")
- Java
-
source
import org.apache.pekko.persistence.jdbc.state.javadsl.JdbcDurableStateStore; import org.apache.pekko.persistence.query.DurableStateChange; import org.apache.pekko.persistence.query.Offset; import org.apache.pekko.projection.state.javadsl.DurableStateSourceProvider; import org.apache.pekko.projection.javadsl.SourceProvider; SourceProvider<Offset, DurableStateChange<AccountEntity.Account>> sourceProvider = DurableStateSourceProvider.changesByTag( system, JdbcDurableStateStore.Identifier(), "bank-accounts-1");
This example is using the DurableStateStore JDBC plugin for Apache Pekko Persistence. You will use the same plugin that you configured for the write side. The one that is used by the DurableStateBehavior
.
This source is consuming all the changes from the Account
DurableStateBehavior
that are tagged with "bank-accounts-1"
. In a production application, you would need to start as many instances as the number of different tags you used. That way you consume the changes from all entities.
The DurableStateChange[AccountEntity.Account]
DurableStateChange<AccountEntity.Account>
is what the Projection
handler will process. It contains the State
and additional meta data, such as the offset that will be stored by the Projection
. See DurableStateChange
DurableStateChange
for full details of what it contains.
SourceProvider for changesBySlices
A SourceProvider
SourceProvider
defines the source of the envelopes that the Projection
will process. A SourceProvider
for the changesBySlices
query can be defined with the DurableStateStoreProvider
DurableStateStoreProvider
like this:
- Scala
-
source
import org.apache.pekko import pekko.persistence.query.DurableStateChange import pekko.persistence.query.Offset import pekko.projection.state.scaladsl.DurableStateSourceProvider import pekko.projection.scaladsl.SourceProvider // Slit the slices into 4 ranges val numberOfSliceRanges: Int = 4 val sliceRanges = DurableStateSourceProvider.sliceRanges(system, R2dbcDurableStateStore.Identifier, numberOfSliceRanges) // Example of using the first slice range val minSlice: Int = sliceRanges.head.min val maxSlice: Int = sliceRanges.head.max val entityType: String = "Account" val sourceProvider: SourceProvider[Offset, DurableStateChange[AccountEntity.Account]] = DurableStateSourceProvider .changesBySlices[AccountEntity.Account]( system, R2dbcDurableStateStore.Identifier, entityType, minSlice, maxSlice)
- Java
-
source
import org.apache.pekko.japi.Pair; import org.apache.pekko.persistence.query.DurableStateChange; import org.apache.pekko.persistence.query.Offset; import org.apache.pekko.projection.eventsourced.javadsl.EventSourcedProvider; import org.apache.pekko.projection.javadsl.SourceProvider; import org.apache.pekko.projection.state.javadsl.DurableStateSourceProvider; // Slit the slices into 4 ranges int numberOfSliceRanges = 4; List<Pair<Integer, Integer>> sliceRanges = EventSourcedProvider.sliceRanges( system, R2dbcDurableStateStore.Identifier(), numberOfSliceRanges); // Example of using the first slice range int minSlice = sliceRanges.get(0).first(); int maxSlice = sliceRanges.get(0).second(); String entityType = "MyEntity"; SourceProvider<Offset, DurableStateChange<AccountEntity.Account>> sourceProvider = DurableStateSourceProvider.changesBySlices( system, R2dbcDurableStateStore.Identifier(), entityType, minSlice, maxSlice);
This example is using the R2DBC plugin for Apache Pekko Persistence. You will use the same plugin that you configured for the write side. The one that is used by the DurableStateBehavior
.
This source is consuming all the changes from the Account
DurableStateBehavior
for the given slice range. In a production application, you would need to start as many instances as the number of slice ranges. That way you consume the changes from all entities.
The DurableStateChange[AccountEntity.Account]
DurableStateChange<AccountEntity.Account>
is what the Projection
handler will process. It contains the State
and additional meta data, such as the offset that will be stored by the Projection
. See DurableStateChange
DurableStateChange
for full details of what it contains.