How to use custom validation class in Grails Application

In this tutorial, we will learn how to add custom validation in the Grails application.

Grails domain classes support the validation by default. So we can simply add the constrains for the domain classes fields as below

class User {
    String username
    String password
    String email
    Integer age
    
    
	static constraints = {
        username blank: false, unique: true
        password size: 5..15, blank: false
        email email: true, blank: false
        age min: 18
	}
}

Now we can simply validate the object using validate() or hasErrors() methods

User user = new User(params) // map the request parameters to user object
if (!user.validate()) {
    // format errors and send to the client
}

User user = new User(params) // map the request parameters to user object
if (user.hasErrors()) {
    // format errors and send to the client
}

Now, let's say that we want to validate some non-domain fields or use a custom validation class to validate the request parameter sent by the user.

We can do so by implementing Validateable trait so that we can add the constrain for the fields in the custom class. Let's look into the example

import grails.validation.Validateable

class UserCommand implements Validateable {

    public static final emailRegex = "^\\w+([\\.-]?\\w+)*@\\w+([\\.-]?\\w+)*(\\.\\w{2,3})+\$"

    UserCommand(def requestParams) {
        email = requestParams.email
        password = requestParams.password
        username = requestParams.username
        age = requestParams.age
    }

    static constraints = {
        username blank: false, unique: true
        password size: 5..15, blank: false
        email email: true, blank: false, validator: emailValidator
        age min: 18
    }
    
    static emailValidator = { String value, UserCommand command ->
        if (!value.find(emailRegex)) {
            return "email.invalid" // getting message from message.properties file
        }
    }
}

In the above example, we can add the constraints after implementing the Validateable on the custom class and do the validation logic similar to the domain classes validation.

Now, let's utilize the above command class inside the controller.

UserCommand userCommand = new UserCommand(requestParams)
        if (!userCommand.validate()) {
            Map result = [success: false, errors: []]
            result.errors = getCommandErrors(userCommand)
            render(result as JSON)
            return
        }

def messageSource

public static List getCommandErrors(def command) {
        List errors = []
        command.errors.allErrors.each { ObjectError error ->
            String msg = messageSource.getMessage(error.code, error.arguments, error.defaultMessage)
            errors.add(msg)
        }
        return errors
    }

For more details visit Grails Validation