https://github.com/calvinlfer/alpakka-cassandra-sink-usage

A demonstration of how to use the Alpakka Cassandra Sink to push case classes through to a Cassandra Table
https://github.com/calvinlfer/alpakka-cassandra-sink-usage

akka-streams cassandra streaming-data

Last synced: about 1 month ago
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A demonstration of how to use the Alpakka Cassandra Sink to push case classes through to a Cassandra Table

• Host: GitHub
• URL: https://github.com/calvinlfer/alpakka-cassandra-sink-usage
• Owner: calvinlfer
• Created: 2018-01-25T02:45:09.000Z (about 7 years ago)
• Default Branch: master
• Last Pushed: 2018-01-25T02:45:43.000Z (about 7 years ago)
• Last Synced: 2025-01-05T08:47:50.220Z (about 1 month ago)
• Topics: akka-streams, cassandra, streaming-data
• Language: Scala
• Size: 3.91 KB
• Stars: 3
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# Using the Alpakka Cassandra Sink #

The Cassandra `Sink` provided by [alpakka](https://developer.lightbend.com/docs/alpakka/current/cassandra.html) is meant

to be used when you want to push elements from your stream into a Cassandra table. The example on the website shows a 

simple use case which persists an integer to a table. Here we look at how we can persist a `case class` to a target table.

```scala

case class Customer(customerId: UUID, age: Int, pay: Long)

```

One big gotcha is figuring out how to write the `BoundStatement` in Scala which involves performing type conversions to 

Java since the underlying Datastax driver that is used to communicate with Cassandra is Java based. 

```scala

  val cassandraSink: Sink[Customer, Future[Done]] = {

    implicit val session: Session = ...

    val insertPreparedStatement: PreparedStatement = session.prepare(s"INSERT INTO customers_by_customer_id(customerId, age, pay) VALUES (?, ?, ?)")

    // you need to convert each Scala type to a Java type when binding values to the prepared statement in order to create the bound statement

    // we deconstruct our Scala case class and explicitly use the Java type instead of the Scala type on the destructured fields

    val statementBinder: (Customer, PreparedStatement) => BoundStatement = (c, ps) => ps.bind(c.customerId: java.util.UUID, c.age: java.lang.Integer, c.pay: java.lang.Long)

    CassandraSink[Customer](parallelism = 10, statement = insertPreparedStatement, statementBinder = statementBinder)

  }

```

## Cassandra Table ##

The Cassandra table schema is provided here:

```cql

CREATE TABLE customers_by_customer_id (

  customerId uuid,

  age int,

  pay bigint,

  PRIMARY KEY((customerid))

);

```

## Local development ##

If you have Docker and Docker Compose installed, just run `docker-compose up` to bring up Cassandra in a Docker 

container.