Overview

Accord is a validation library written in and for Scala. Compared to JSR 303 and Scalaz validation it aims to provide the following:

• Composable: Because JSR 303 is annotation based, validation rules cannot be composed (annotations cannot receive other annotations as parameters). This is a real problem with some Scala features, for example Options or collections. Accord's validation rules are trivially composable.
• Simple: Accord provides a dead-simple story for validation rule definition by leveraging macros, as well as the validation call site (see example below).
• Self-contained: Accord is macro-based but completely self-contained, and consequently only relies on the Scala runtime and reflection libraries.
• Integrated: Other than providing its own DSL and matcher library, Accord is designed to easily integrate with other libraries, and provides out-of-the-box integration with Spring Validation, Specs² and ScalaTest.

Accord is developed and used at and distributed under the Apache License, Version 2.0, which basically means you can use and modify it freely. Feedback, bug reports and improvements are welcome!

Example

Importing the library for use:

import com.wix.accord._

Defining a validator:

import dsl._    // Import the validator DSL

case class Person( firstName: String, lastName: String )
case class Classroom( teacher: Person, students: Seq[ Person ] )

implicit val personValidator = validator[ Person ] { p =>
  p.firstName is notEmpty                   // The expression being validated is resolved automatically, see below
  p.lastName as "last name" is notEmpty     // You can also explicitly describe the expression being validated
}

implicit val classValidator = validator[ Classroom ] { c =>
  c.teacher is valid        // Implicitly relies on personValidator!
  c.students.each is valid
  c.students have size > 0
}

Running a validator:

scala> val validPerson = Person( "Wernher", "von Braun" )
validPerson: Person = Person(Wernher,von Braun)

scala> validate( validPerson )
res0: com.wix.accord.Result = Success

scala> val invalidPerson = Person( "", "No First Name" )
invalidPerson: Person = Person(,No First Name)

scala> validate( invalidPerson )
res1: com.wix.accord.Result = Failure(List(RuleViolation(,must not be empty,firstName)))

scala> val explicitDescription = Person( "No Last Name", "" )
explicitDescription: Person = Person(No Last Name,)

scala> validate( explicitDescription )
res2: com.wix.accord.Result = Failure(List(RuleViolation(,must not be empty,last name)))

scala> val invalidClassroom = Classroom( Person( "Alfred", "Aho" ), Seq.empty )
invalidClassroom: Classroom = Classroom(Person(Alfred,Aho),List())

scala> validate( invalidClassroom )
res3: com.wix.accord.Result = Failure(List(RuleViolation(List(),has size 0, expected more than 0,students)))

Getting Started

Accord version 0.4.2 is available on Maven Central Repository. Scala versions 2.10.3+ and 2.11.x are supported. The next milestone is 0.5-SNAPSHOT and is available from the Sonatype snapshots repository.

SBT

Simply add the accord-core module to your build settings:

libraryDependencies += "com.wix" %% "accord-core" % "0.4.2"

If you want to evaluate the upcoming snapshot release, add the Sonatype snapshot repository to your resolvers; typically this means adding the following to your build.sbt file:

resolvers += "Sonatype OSS Snapshots" at "https://oss.sonatype.org/content/repositories/snapshots"

libraryDependencies += "com.wix" %% "accord-core" % "0.5-SNAPSHOT"

Maven

Accord is published to the Maven Central Repository, so you simply have to add the appropriate dependency to your POM:

<dependencies>
  <dependency>
    <groupId>com.wix</groupId>
    <artifactId>accord-core_${scala.tools.version}</artifactId>
    <version>0.4.2</version>
  </dependency>
</dependencies>

If you want to evaluate the upcoming snapshot release, add the Sonatype snapshot repository and a dependency on Accord to your POM:

<repositories>
  <repository>
    <id>sonatype-snapshots</id>
    <name>Sonatype snapshot repository</name>
    <url>https://oss.sonatype.org/content/repositories/snapshots</url>
    <releases><enabled>false</enabled></releases>
    <snapshots><enabled>true</enabled></snapshots>
  </repository>
</repositories>

<dependencies>
  <dependency>
    <groupId>com.wix</groupId>
    <artifactId>accord-core_${scala.tools.version}</artifactId>
    <version>0.5-SNAPSHOT</version>
  </dependency>
</dependencies>

Roadmap

Accord is still fairly rudimentary, and there's plenty of improvements to be made:

• Major issues and improvements planned or under consideration for the 0.5 milestone release:
  • #6 Support inline expressions in validators
  • #19 Scala.js support
  • #21 i18n support
  • Rethink binary expression API so that arbitrary types can be used
• Future plans:
  • Elide DSL implicit invocations from resulting tree for better performance and smaller code
  • Add syntax for custom violation message overrides (e.g. p.firstName is notEmpty as "no first name!")
  • Support custom violation types (e.g. p.firstName is notEmpty as MyServerError( code = -3 ))
  • Add a validation result rendering framework
  • Implement accord-hamcrest integration in a separate artifact
  • Add adapter for Specs² matcher module

Ideas and feature requests welcome!