Adding your own error message to a Grails Command Object

Here is another little trick I got to use in Grails recently:

Before I started using Grails I used Spring MVC and in fact i still do i my day job. Any way one of the things Spring provided was the Errors interface. This allowed you to add your own error message that would end up available to your view layer. By using methods such as

reject() and rejectValue()

So as Grails is built on top of Spring it also makes use of the Errors interface and it automatically injects an instance of this into your domain objects and command objects.

So in your controller if you want add an error message to your command object (eg HolidayQueryCommand)

Then all you have to is this:

holidayQueryCommand.errors.reject("message.code","default error message");

If you wanted to attach and error message to a particular property then do this:

holidayQueryCommand.errors.rejectValue("property","message.code","default error message");

These error messages are then all available in your GSP:

<g:rendererrors bean="${holidayQueryCommand}" as="list"></g:rendererrors>

That also goes for domain objects too not just command objects.

If this is useful to even 1 person then i am glad i posted it :)