ZIO Schema

ZIO Schema is a ZIO-based library for modeling the schema of data structures as first-class values.

Introduction

Schema is a structure of a data type. ZIO Schema reifies the concept of structure for data types. It makes a high-level description of any data type and makes them as first-class values.

Creating a schema for a data type helps us to write codecs for that data type. So this library can be a host of functionalities useful for writing codecs and protocols like JSON, Protobuf, CSV, and so forth.

With schema descriptions that can be automatically derived for case classes and sealed traits, ZIO Schema will be going to provide powerful features for free (Note that the project is in the development stage and all these features are not supported yet):

Codecs for any supported protocol (JSON, protobuf, etc.), so data structures can be serialized and deserialized in a principled way
Diffing, patching, merging, and other generic-data-based operations
Migration of data structures from one schema to another compatible schema
Derivation of arbitrary type classes (Eq, Show, Ord, etc.) from the structure of the data

When our data structures need to be serialized, deserialized, persisted, or transported across the wire, then ZIO Schema lets us focus on data modeling and automatically tackle all the low-level, messy details for us.

ZIO Schema is used by a growing number of ZIO libraries, including ZIO Flow, ZIO Redis, ZIO Web, ZIO SQL and ZIO DynamoDB.

Installation

In order to use this library, we need to add the following lines in our build.sbt file:

libraryDependencies += "dev.zio" %% "zio-schema"          % "0.4.13"
libraryDependencies += "dev.zio" %% "zio-schema-bson"     % "0.4.13"
libraryDependencies += "dev.zio" %% "zio-schema-json"     % "0.4.13"
libraryDependencies += "dev.zio" %% "zio-schema-protobuf" % "0.4.13"

// Required for automatic generic derivation of schemas
libraryDependencies += "dev.zio" %% "zio-schema-derivation" % "0.4.13",
libraryDependencies += "org.scala-lang" % "scala-reflect"  % scalaVersion.value % "provided"

Example

In this simple example first, we create a schema for Person and then run the diff operation on two instances of the Person data type, and finally we encode a Person instance using Protobuf protocol:

import zio.console.putStrLn
import zio.schema.codec.ProtobufCodec._
import zio.schema.{DeriveSchema, Schema}
import zio.stream.ZStream
import zio.{Chunk, ExitCode, URIO}

final case class Person(name: String, age: Int, id: String)
object Person {
  implicit val schema: Schema[Person] = DeriveSchema.gen[Person]
}

Person.schema

import zio.schema.syntax._

Person("Alex", 31, "0123").diff(Person("Alex", 31, "124"))

def toHex(chunk: Chunk[Byte]): String =
  chunk.toArray.map("%02X".format(_)).mkString

zio.Runtime.default.unsafe.run(
  ZStream
    .succeed(Person("Thomas", 23, "2354"))
    .transduce(
      encoder(Person.schema)
    )
    .runCollect
    .flatMap(x => putStrLn(s"Encoded data with protobuf codec: ${toHex(x)}"))
).getOrThrowFiberFailure()

Resources

Zymposium - ZIO Schema by John A. De Goes, Adam Fraser and Kit Langton (May 2021)

Documentation

Learn more on the ZIO Schema homepage!

Contributing

For the general guidelines, see ZIO contributor's guide.

TL;DR

Before you submit a PR, make sure your tests are passing, and that the code is properly formatted

sbt prepare

sbt test

devsprint/zio-schema