CODEWITHSUNDEEP
grailscontroller
Matt Westlake
Matt Westlake

Reputation: 3651

Grails pass object to the view and back again

I have some data that I need to persist through multiple actions within my Grails app. Due to the nature of the data, I would prefer not to store the data in the session. Here is an example of what I would like to do.

class MyController{
  def index(){
    MyObject object = MyObject.new(params.first, params.second, params.third)
    [gspObject:object]
  }

  def process(){
    MyObject object = params.gspObject
    //continue from here
  }
}

In my GSP if I do

<g:form action="process" params="[gspObject:gspObject]">

Then I get the error 

Cannot cast object 'net.package.MyObject@699c14d8' with class 'java.lang.String' to class 'net.package.MyObject'

My question is, If I want to get the object back that I sent to the gsp, how can I get that? Is there some kind of scope that I can save the object in that would be a little safer then session? Is there a way to pass the object into the page itself and pass it back in the next request?

Upvotes: 2

Views: 2443

Answers (1)

Burt Beckwith
Burt Beckwith

Reputation: 75681

Grails has many layers, but at the bottom you have plain old HTTP just like in any web app. It's a stateless protocol, and you send a text or binary response, and receive text or text + binary requests. But you can't expect to be able to send an arbitrary object to a web browser in HTML and receive it back again in the same state as when you sent it - where is this Java/Groovy JVM object going to be stored in the browser?

You have basically two options. One is to store it at the server, which is less work because it remains as the same object the whole time. The session is a good location because it's coupled to the user, is created on-demand and can automatically time out and be removed, etc. The other is to do what you're trying to do - send it to the client and receive it back - but you are going to have to serialize it from an object (which could be a complex object containing arbitrarily many other objects) and deserialize it from the format you used on the client back into Java/Groovy objects.

JSON is a good option for serialization/marshalling. You could store the stringified object in a hidden form element if your page uses a form, or in a querystring arg if you click a link from this page to the next in the workflow. Don't send all of the object's data though, only what you need to rebuild it. Anything that's available in the database should be referenced by id and reloaded.

Something like

[gspObject: object as JSON]

or

[gspObject: [first: object.first, first: object.firstsecond,  ...] as JSON]

will get it in the correct format for sending, and then you can parse the JSON from the request to reinstantiate the instance.

Upvotes: 6

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