Controller action implicitly called when rendering template without a model?

[Ted Vinke]

Today I was confronted by some odd behaviour in my Grails 2.3.6 application: when rendering a template in a controller action without specifying a model other controller action(s) is/are invoked too automatically. A small contrived example shows what I mean. A controller with an index() action - for rendering an "_index.gsp" snippet - and another action getSomethingElse() which renders "something else".

controllers/test/RenderController with explicit empty model

class RenderController {
 
    def index() {
        render template: "index", model: [:] // <-- explicit empty model
    }
 
 
    def getSomethingElse() {
        render "something else"
    }
}

views/render/_index.gsp

<h1>Hello from the _index.gsp</h1>

When http://localhost:8080/RenderTest/render is invoked, just the contents from the _index.gsp are shown:

Hello from the _index.gsp

As expected.

When I leave out the model attribute to the template rendering...

def index() {
    render template: "index" // <-- no model
}

...suddenly the getSomethingElse() method is invoked too, just before that. When reloading the page, "something else" is rendered, followed by the contents on my index-snippet:

something else
Hello from the _index.gsp

What I did NOT expect is that basically every additional action - in this controller - starting with "get" seems to be invoked before my render, that's at least the pattern I can see here, if I do not explicitly define a model passed to the "render" method.

I went through the Grails documentation and Grails JIRA, but couldn't find any documentation about this feature, or ticket to a bug, nor any reference from the Grails docs to leveraging any existing Spring MVC feature.

Who can help me finding where this behavior is documented?

Kind regards, 

Ted

[Graeme Rocher]

This is an old feature that will be removed in Grails 3.0

If no model is specified the controllers properties become the model.
Because a getter is a property your action is invoked. This behaviour
has indeed caused much confusion amongst users and hence why it will
be removed in Grails 3.0

Cheers

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--
Graeme Rocher
Grails Project Lead
Pivotal

[Ted Vinke]

Thanks for the quick response, Greame!

Is this feature documented somewhere? Or maybe a JIRA issue about it's pending removal in Grails 3.0?

Cheers

[Graeme Rocher]

Reference to it can be found in older user guides. Example in 2.1.x

http://grails.org/doc/2.1.0/guide/single.html#controllers

See "Returning the model" and the line:

"If no explicit model is returned the controller's properties will be
used as the model"

This was removed from the user guide however since the behaviour is
regarded as deprecated as we didn't want to encourage its use.

Cheers

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[Paco Zarate]

This behavior caused me problems too, what is the right way to proceed on grails 2.x? Do not use the 'get' prefix on the method names?

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[Ted Vinke]

Ha Paco,

It seems that whatever you do depends on your application.

1) Renaming your 'getXXX'' into 'findXXX' might be an option - e.g. if you have a few occurrences and you don't mind this renaming

2) Adding an explicit empty model attribute ("model: [:]") - where I previously had none defined, and which triggered this behaviour - worked for me. Just one occurrence needed replacing.

In all cases I had to communicate this with the team, to be aware of this feature :-)

Regards, Ted

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[Paco Zarate]

Hey Ted! Thanks for your suggestions.

I will try the empty model approach. I have a lot of get methods on my REST API and I have the map pointing to the renamed method but it seems more natural if i can keep the names with the get.

Thanks again

Paco

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