Grails GORM Mongo hasMany association not saved

Question

I have a domain class with a one-to-many association. It looks like so:

class FormResponse {

    static String DRAFT = 'Draft'
    static String SUBMITTED = 'Submitted'
    static String REJECTED = 'Rejected'
    static String APPROVED = 'Approved'

    static mapWith = "mongo"

    ObjectId id
    Date dateCreated
    Date lastUpdated
    User createdBy
    User updatedBy
    Form form
    String currentStatus = DRAFT
    List<FormSectionResponse> formSectionResponses
    List<FormResponseComment> formResponseComments

    static hasMany = [ formSectionResponses: FormSectionResponse, formResponseComments: FormResponseComment ]

    static mapping = {
    }

    static constraints = {
        updatedBy nullable: true
    }

}

The domain class for FormResponseComment:

class FormResponseComment {

    static mapWith = "mongo"

    ObjectId id
    Date dateCreated
    Date lastUpdated
    User createdBy
    String comment

    static belongsTo = [FormResponse]

    static mapping = {
    }

    static constraints = {
    }

}

I have a controller method for saving this object which looks like so:

def saveFormResponse(FormResponse formResponse) {
   def saved = formService.saveFormResponse(formResponse)
   respond(saved)
}

And the service method:

def saveFormResponse(response) {
    return response.save(flush: true, failOnError: true)
}

When I post to this method, I can see the formResponseComments list populated as I expect it to be:

And the FormResponseComment is saved:

But the FormResponse object does not receive an association to the child FormResponseComment:

So why is the association not made here?

Grails 3.3.3.

Answer 1

Fixed by adding a back reference to the FormResponseComment domain class like so:

static belongsTo = [formResponse: FormResponse]