Is this a valid use of Grails transients?

domain-object, grails, transient

Solution

Transients are indeed used to stop fields in domain objects from being persisted. (If you want to perform some init on the `pal` field without having to put it in your controller you could use the `onLoad()` event or write a `getPal()` method which would override the default property getter). You are also right to note that the default JSON marshaller only renders persisted fields.

When rendering my domain objects I've found it useful to create JSON object marshallers so that unwanted properties are not rendered, but it would also solve your transient issue too. You can do this using the `JSON.registerObjectMarshaller` method:

import grails.converters.JSON
...
class BootStrap {

    def init = {servletContext ->
        JSON.registerObjectMarshaller(Contact ) {
            def returnArray = [:]
            returnArray['id'] = it.id
            returnArray['initiatedDate'] = it.initiatedDate
            returnArray['acceptedDate'] = it.acceptedDate
            returnArray['pal'] = it.pal
            return returnArray
        }

        JSON.registerObjectMarshaller(Seeker) {
            ...
        }

If you add the marshallers in your `BootStrap.groovy` they will be available in your controllers.

HTH

(Also found this: http://old.nabble.com/Taggable-plugin-and-JSON-converter-ts24830987.html#a24832970)

Problem

I have a domain object on which I want to store a few things which only exist at runtime. I looked at the documentation and found the `transients` keyword, which, on the face of it was what I was looking for. Here is what my domain object looks like... ``` class Contact { def Seeker def beforeInsert() { initiatedDate = new Date() } Date initiatedDate Date acceptedDate static transients = ['pal'] Seeker pal } ``` where `Seeker` is a groovy class which is not a domain object, but a placeholder for some properties. So far all is fine and my Contact table does not have a `pal` field as expected. In my `ContactController` I query for a bunch of contacts, `c`, then look up their `Seeker` pals (details of how withheld) and set the `pal` field to a new object. ``` c.pal = new Seeker(); c.pal.name = otherObject.name render c as JSON ``` This all seems to work fine except that the pal object is missing from the JSON returned. Is this a valid use of transients? The docs mention that they are handy for function-based getters and setters, but in my case I want an actual object. Should I be writing a getPal() and setPal() method on my object? Thanks

Original source