1. 首先需要添加以下依赖项：

libraryDependencies += "com.typesafe.akka" %% "akka-persistence-jdbc" % "5.0.0"

2. 在 application.conf 文件中添加以下内容：

akka.projection.jdbc {
  # JDBC driver class to use
  driver = "org.postgresql.Driver"

  # Database url
  url = "jdbc:postgresql://localhost:5432/dbname"

  # Database user/password
  user = ""
  password = ""

  # Connection pool parameters
  connectionPool {
    # Maximum number of connections to allocate
    maxSize = 5

    # Maximum time to wait for a free connection from the pool
    maxQueueSize = 10

    # Maximum time to wait when connection pool is full and no connection is available
    connectionTimeout = 10s
  }
}

3. 创建一个数据库连接，并将其传递给 ActorSystem。可以在应用程序启动时创建连接，并将其传递给 ActorSystem，或者在 Projection 的实现中提供一个方法来创建连接。

import slick.jdbc.PostgresProfile.api._

val db = Database.forConfig("akka.projection.jdbc")

val system = ActorSystem("my-project", config)

// 或者

val system = ActorSystem("my-project", config.withFallback(Configuration.fromDb(db)))

4. 在 Projection 中添加 JDBC 处理程序并使用它：

import akka.stream.scaladsl.Source
import akka.projection.ProjectionBehavior
import akka.projection.ProjectionId
import akka.projection.eventsourced.EventEnvelope
import akka.projection.eventsourced.EventEnvelopeProjection
import akka.projection.jdbc.scaladsl.JdbcHandler

case class MyProjectionHandler(db: Database) extends JdbcHandler[EventEnvelope[MyEvent]] {

  override def process(session: Session, envelope: EventEnvelope[MyEvent]): Unit = {
    // 处理事件并将其写入数据库
  }
}

val projection = EventEnvelopeProjection
  .atLeastOnceSource(() => Source.from(myEventSource), projectionId)
  .withProjectionBehavior(ProjectionBehavior.fromFunctionHandler(MyProjectionHandler(db)))