Grails min constraint for date validation

I am a newbie in grails and groovy. I have a Project domain-class with start and end date. I want to put in a constraint specifying that the end date needs to be greater than the start date(and then further another child object of project needs to have its startdate and enddate validate with the parent Project's dates). Is this possible with the min constraint or do I have to put it elsewhere? Unique constraint does allow two properties to be linked that way, hoping min/max constraints开发者_运维技巧 allow that. I have tried

startDate(blank:false)
endDate(blank:false, min:'startDate')

It throws an error saying the property startDate is not available on Project

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Try using a custom validator:

static constraints = {
    endDate(validator: { val, obj ->
        val?.after(obj.startDate)
    })
}

val is the value of the field and obj is a reference to the object being validated. The closure can contain whatever logic you need, so you can extend your validation in the way you're describing in your question (by accessing the child objects you refer to using obj).

The custom validator is pretty flexible. Have a look at the documentation. Ideally you'll want to return a custom message; how to do that can also be found in the docs linked above.