Where does Grail's errors property come from?

Question

Grails has a bug with regards to databinding in that it throws a cast exception when you're dealing with bad numerical input. JIRA: http://jira.grails.org/browse/GRAILS-6766

To fix this I've written the following code to manually handle the numerical input on the POGO class Foo located in src/groovy

void setPrice(String priceStr)
{
    this.priceString = priceStr

    // Remove $ and , 
    priceStr = priceStr.trim().replaceAll(java.util.regex.Matcher.quoteReplacement('$'),'').replaceAll(',','')

    if (!priceStr.isDouble()) {
        errors.reject(
            'trade.price.invalidformat',
            [priceString] as Object[],
            'Price:[{0}] is an invalid price.')

        errors.rejectValue(
            'price',
            'trade.price.invalidformat')
    } else {
        this.price = priceStr.toDouble();
    }
}

The following throws a null reference exception on the errors.reject() line.

foo.price = "asdf" // throws null reference on errors.reject()
foo.validate()

However, I can say:

foo.validate()
foo.price = "asdf" // no Null exception
foo.hasErrors() // false
foo.validate()
foo.hasErrors() // true

Where does errors come from when validate() is called? Is there a way to add the errors property without calling validate() first?

Answer 1

I can't exactly tell you why, but you need to call getErrors() explicitly instead of accessing it as errors like a property. For some reason, Groovy isn't calling the method for it. So change the reject lines in setPrice() to

getErrors().reject(
        'trade.price.invalidformat',
        [priceString] as Object[],
        'Price:[{0}] is an invalid price.')

getErrors().rejectValue(
        'price',
        'trade.price.invalidformat')

That is the easiest way to make sure the Errors object exists in your method. You can check out the code that adds the validation related methods to your domain class.

Answer 2

The AST transformation handling @Validateable augments the class with, among other things

• a field named errors
• public methods getErrors, setErrors, clearErrors and hasErrors

The getErrors method lazily sets the errors field if it hasn't yet been set. So it looks like what's happening is that accesses to errors within the same class are treated as field accesses rather than Java Bean property accesses, and bypassing the lazy initialization.

So the fix appears to be to use getErrors() instead of just errors.