Chris Evans

On Grails domain classes it’s possible to declare variables as transient (i.e. should not be persisted to the database) by using the transients property:

static transients = ['firstName']

Oftentimes its desirable to declare properties on command objects and exempt them from binding/validation in a similar manner.

I found this was possible in the following way:

class SubmitDetailsCommand {
 
String name 
String address 
 
String previousAddress 
 
static constraints = {
    previousAddress nullable: true, bindable: false
}

Using this the name and address fields will be bound and validated, but the previousAddress won’t be bound (and will pass validation). I also found that no validation errors were raised even without the nullable declaration when previousAddress‘ type was explicitly declared (in my case I was using List, as opposed to this example), but the validation errors occurred when it was def.

Alternatively if the transient property is to be used as part of custom validation (which, when the controller’s method parameter is a type of command object is performed before even the first line of code in the method), as in the following:

class SubmitDetailsCommand {
 
String name 
String address 
 
String previousAddress 
 
static constraints = {
    address validator: { address, command -> address != previousAddress }
    previousAddress nullable: true, bindable: false
}

The following technique can be used:

def controllerMethod() {
 
    def command = new SubmitDetailsCommand()
    bindData(command, params << [previousAddress: session.usersPreviousAddress], [include: ['name', 'address', 'previousAddress']])
 
    command.validate()
 
    if (command.hasErrors()) {
        ...
    }
 
    ...
}

Unfortunately the implicit binding/validation and the nice convention of declaring it as a method parameter is not being leveraged, but this was the best solution I found. This technique was useful when the method was part of a web flow which relied on values deduced in previous stages on the flow.