Fields

Fields is a Scala validation library that you should use because it is:

• Final Tagless. Choose any Effect, Validated, or Error types.
• Informative. Error paths help understanding where the error occurred.
• Expressive. Rich, extendable validation syntax.
• Lightweight. The core module has no-dependencies.
• Dauntless. Have no fear of complex validations with Rule type.
• Short-circuit. Avoid running undesired validation side-effects.

Teaser

// Here we pass validation dependencies using implicits, but you could be doing this the way you prefer
def policy(implicit tokenService: TokenService, userService: UserService): Policy[RegisterRequest] = Policy
  .builder[RegisterRequest]
  .subRule(_.age)(_ >= 18, _ <= 110)
  .subRule(_.email)(_.map(_.value).matchesRegex(EmailRegex))
  .subRule(_.password)(_.nonEmpty, _.minSize(4), _.maxSize(100))
  .subRule(_.password, _.passwordRepeat)(_ equalTo _)
  .subRule(_.username)(validateUsername)
  .subRule(_.token)(_.ensureF(tokenService.validateToken, _.failMessage("invalid-token")))
  .build

// Extract complex validations to reusable methods.
def validateUsername(username: Field[String])(implicit userService: UserService): MRule =
    username.minSize(1) &&
    username.maxSize(10) &&
    MRule.flatten {
      userService.findByUsername(username.value).map {
        case Some(_) => username.failMessage("username-already-exists")
        case None    => MRule.valid
      }
    }

Quicklinks

• Microsite
• Medium
• Contributor's Guide
• License
• Issues
• Pull Requests

Learn More on the Fields Microsite