Using command objects in Grails is a simple way to perform data binding and validation when there is no need to create domain object. In this tutorial I will show you some examples of using it.
First thing you‘ll need to do is describe your command object. It is fine to do in the same file that contains controller that will use it. If command will be used by more than one controller, describe it in controllers or in groovy source directory.
Note: all the code below is written and tested against Grails 1.3.7
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class RegisterCommand {
String login
String email
String password
String confirmationPassword
static constraints = {
login size: 1..250, blank: false
email size: 1..250, email: true, blank: false
password size: 6..20, blank: false
confirmationPassword size: 6..20, blank: false, validator: RegisterController.passwordValidator
}
static final def passwordValidator { String value, command ->
if (command?.password != command?.confirmationPassword) {
//returning message code for i18n/messages.properties file
return 'registerCommand.confirmationPassword.mismatch'
}
true
}
}
Next thing you’ll probably want to do, is bind the data, that is being
received by action in your controller to the command object and validate
it.
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def registerAction = { RegisterCommand command -> // data binding and validation
//checking errors
if (command.hasErrors()) {
render view: 'register', model: [command: command]
} else {
//do something
}
}
To view errors that may appear during command validation, specify
following code in your .gsp page.
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<g:textField name="confirmationPassword" bean="${command}"/>
<g:hasErrors bean="${command}" field="confirmationPassword">
<s2ui:fieldErrors bean='${command}' field=”confirmationPassword”/>
</g:hasErrors>
Now this is a pretty common usage of command objects, but you may need
some more functionality. You can check not only whether there is any
error in command, but also what are these errors, reject error in case
if they may appear during action, check field for the error, clear all
the errors and so on.
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//checking is specified login already exists
if (Account.findByLogin(command.login)) {
//rejects error for field in command, which validation has failed
command.errors.rejectValue('login', 'registerCommand.login.exists')
}
//checks is specified field contains invalid value
if (command.errors.hasFieldErrors('email')) {
//do something
}
//shows errors
command.getErrors()
//clears errors
command.clearErrors()