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scalaz-stream + jdbc
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| import java.sql.DriverManager | |
| import scalaz.concurrent.Task | |
| import scalaz.stream.io | |
| import scalaz.stream.Process.End | |
| class Query(query: String, chunkSize: Int) { | |
| Class forName "org.postgresql.Driver" | |
| val connection = DriverManager.getConnection(url, "username", "password") | |
| val statement = connection.createStatement | |
| // This will cause the postgres driver to create a cursor and give ResultSets of that size | |
| statement.setFetchSize(chunkSize) | |
| val resultSet = statement.executeQuery(query) | |
| def next = resultSet.next | |
| def isAfterLast = resultSet.isAfterLast | |
| def getString(i:Int) = resultSet.getString(i) | |
| def close { | |
| resultSet.close | |
| statement.close | |
| connection.close | |
| } | |
| } | |
| val chunkSize = 100 | |
| val query: scalaz.stream.Process[Task, IndexedSeq[String]] = io.resource( | |
| Task.delay(new Query("select * from foo", chunkSize)) | |
| )(rs => | |
| Task.delay(rs.close) | |
| )(rs => | |
| Task.delay{ | |
| if (rs.isAfterLast) throw End | |
| for (_ <- 1 to chunkSize if rs.next) yield rs.getString(1) | |
| } | |
| ) |
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