Grails 3.3.1 Controller action with domain object argument - how is data bound?

Question

This question looks somewhat similar, but the asker there was attempting to understand how a one-to-many data binding works when the Domain object is a Controller action argument.

I want to understand, under-the-hood, what methods are being invoked when the Domain class is provided as an argument to a Controller action. Consider the default update action:

def update(MyDomain myDomain) {
    if (myDomain == null) {
        notFound()
        return
    }

    try {
        myDomainService.save(myDomain)
    } catch (ValidationException e) {
        respond myDomain.errors, view:'edit'
        return
    }

    request.withFormat {
        form multipartForm {
            flash.message = message(code: 'default.updated.message', args:
                [message(code: 'myDomain.label', default: 'MyDomain'), myDomain.id])
            redirect myDomain
        }
        '*'{ respond myDomain, [status: OK] }
    }
}

What is the sequence of events leading up to the scope of the above Controller action? My best guess is below, but I would like confirmation.

def someActionWrapper() {
    MyDomain instance = MyDomain.get(params.id)
    instance.properties = params
    update(instance)
}

I think it must be going to the DB to pick up any fields that weren't on the form, then overwriting with any values that were on the form, then calling the actual controller action.

Edit

Current versions of libraries when this question was asked:

Grails 3.3.1
Groovy 2.4.12

"I think it must be going to the DB to pick up any fields that weren't on the form, then overwriting with any values that were on the form, then calling the actual controller action." - That is kind of true. It is going to the database to retrieve all of the fields, not just the ones that weren't on the form. My answer below provides more details. — Jeff Scott Brown

Jeff Scott Brown Jeff Scott Brown · Accepted Answer · 2017-10-02T20:30:42

See https://github.com/grails/grails-core/blob/96c530ab4400f28a4cc0001b2bacbbce1e360cc1/grails-plugin-controllers/src/main/groovy/grails/artefact/Controller.groovy#L345.

In short...

// This is pseudocode but it addresses the broad strokes of what you are asking about...
MyDomain md
if(params.id) {
    md = MyDomain.get(params.id)
} else if (request.method == 'POST') {
    md = new MyDomain()
}

if(md) {
    def doBinding = true
    if(params.id) {
        if(!(request.method in ['PUT', 'POST', 'DELETE'])) {
            doBinding = false
        }
    }

    if(doBinding) {
        // params won't necessarily be used here
        // if the request has a body, it will be used
        bindData md, params
    }

    // subject md to dependency injection

    // if md is Validateable then call .validate() on it
}

callToTheOriginalAction(md)

Grails 3.3.1 Controller action with domain object argument - how is data bound?

Edit

1 Answers