view doesn't detect error in passed in model object - grails

Question

The code in controller is as follows:
for(o in options){
if(o){
if(!o.isInteger()){
don.errors.reject("The value was not integer")
render(view: "editdonation", model: [id:id, donation:don])
return
}
don.addToDenominations(o.toInteger())
}
}
I intentionally pass in invalid input so that the don.errors.reject() code is executed.
The editdonation.gsp has the following code to print the error in the donation object.
<ul class="inline-errors" role="alert">
<g:hasErrors bean="${donation}">
<div class="errors">
ok it has errors
</div>
</g:hasErrors>
</ul>
Why is the view not displaying the error? I appreciate any help!

Answer 1

The Errors.reject() method expects an error code rather than an error description.
Creating the error code
To create your own error code:
Edit the file grails-app/i18n/message.properties
Add a new line with your error code. Ex: option.donation.notinteger=The option value {0} was not an Integer
Save the file grails-app/i18n/message.properties
Using the error code
To use the error code, call Errors.reject() like this:
don.errors.reject('option.donation.notinteger', [o] as Object[], 'The value was not integer')
The code above passes the option to reject so that it can insert the value into the error message. And as required, it provides a fallback error message.