Add constraints to properties of Groovy class (not Grails domain class!)

Question

How can we add some common constraints (i.e. maxLength, nullable) to a property of a Groovy class? I know we can do it at Grails domain class, but is it possible if that is a Groovy class (I use it as a DTO class for my Grails project)?
Thank you so much!

Answer 1

You can add constraints to command classes. If a command class is in the same .groovy file as a controller (in Groovy you can have more than one public class in each .groovy file), you don't need to do anything special for Grails to recongise it as a command class.

However, if your command class is somewhere else (e.g. under src/groovy), you need to annotate it with @Validateable and add the package name to the grails.validateable.packages parameter in Config.groovy. Here's an example of a command that's not in the same file as a controller

pacakge com.example.command

@Validateable
class Person {
  Integer age
  String name

  static constraints = {
    name(blank: false)
    age(size 0..100)
  }
}

Add the following to Config.groovy

grails.validateable.packages = ['com.example.command']

Command classes have a validate() method added by Grails. After this method is called, any errors will be available in the errors property (as per domain classes).