Summary

A ZQuery[R, E, A] is a purely functional description of an effectual query that may contain requests from one or more data sources, requires an environment R, and may fail with an E or succeed with an A.

Requests that can be performed in parallel, as expressed by zipWithPar and combinators derived from it, will automatically be batched. Requests that must be performed sequentially, as expressed by zipWith and combinators derived from it, will automatically be pipelined. This allows for aggressive data source specific optimizations. Requests can also be deduplicated and cached.

This allows for writing queries in a high level, compositional style, with confidence that they will automatically be optimized. For example, consider the following query from a user service.

lazy val getAllUserIds: ZQuery[Any, Nothing, List[Int]]    = ???
def getUserNameById(id: Int): ZQuery[Any, Nothing, String] = ???

lazy val userQuery: ZQuery[Any, Nothing, List[String]] = for {
  userIds   <- getAllUserIds
  userNames <- ZQuery.foreachPar(userIds)(getUserNameById)
} yield userNames

This would normally require N + 1 queries, one for getAllUserIds and one for each call to getUserNameById. In contrast, ZQuery will automatically optimize this to two queries, one for userIds and one for userNames.

Installation

Include ZIO Query in your project by adding the following to your build.sbt file:

libraryDependencies += "dev.zio" %% "zio-query" % "0.2.0"