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class PostsController < ActionController::Base
def create
Post.create(post_params)
end
def update
Post.find(params[:id]).update_attributes!(post_params)
end
private
def post_params
params[:post].slice(:title, :content)
end
end
@sentientmonkey
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sentientmonkey commented Mar 5, 2012

I thought the proper way of doing this was using presenters & delegating fields you want to change on a per-use case basis. Is this not common practice??

@alassek
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alassek commented Mar 5, 2012

Am I the only one who does this?

class PostsController < ActionController::Base
  def create
    Post.create(params[:post], :as => current_role)
  end

  def update
    @post = Post.find(params[:id])
    @post.assign_attributes(params[:post], :as => current_role).save!
  end
end

The post_params approach wouldn't work well for me, because a lot of my forms have two or three levels of nesting. That would mean a lot of repetition of parameter lists.

@larzconwell
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larzconwell commented Mar 5, 2012

@alassek I use that for approach when checking to use admin attribute or not. But I don't think it is that flexible.

@sheldonh
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sheldonh commented Mar 5, 2012

For me, this tickles an itch. I have a nagging suspicion that this rule would drive deeper domain model design: never call AR methods from outside your AR objects. I'm not sure yet that it's a useful rule to adhere to religiously, but I think it's a useful thought experiment.

@petervandenabeele
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petervandenabeele commented Mar 5, 2012

Another use case for this approach (of slicing in the controller) I had is that the HTML and XML interface for the same model have slightly different "access rights" to the fields. So that is also a "controller driven" slicing of the access to the fields. On the other hand, the model tests should be able to access all fields freely.

@gma
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gma commented Mar 5, 2012

I use slice too. But what's this comment about, from the Rails source?

Note that using Hash#except or Hash#slice in place of attr_accessible to sanitize attributes won't provide sufficient protection.

https://github.com/rails/rails/blob/master/activemodel/lib/active_model/mass_assignment_security.rb#L171

I can only imagine they're thinking of nested attributes (which I slice up as well, on the rare occasions that I use them).

@adnanced
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adnanced commented Mar 5, 2012

Or you could use principles from some other frameworks (which I wont mention here) and that is:

"You cannot mass assign attribute that have no validation rule assigned to it"

It is perfectly logical and works like a charm.
This way you are making whitelist for security hole instead of blacklisting it. And if you want to mass assign attribute that have no validation (rare cases) you can assign "safe" validator which is just dummy validation rule.

@diegorv
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diegorv commented Mar 5, 2012

attr_accessible is already available in controller isn't? http://api.rubyonrails.org/classes/ActiveModel/MassAssignmentSecurity/ClassMethods.html

@sobrinho
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sobrinho commented Mar 5, 2012

@diegorv it only works for controller that handles a single resource.

nested resources will be a problem :)

@wxianfeng
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wxianfeng commented Mar 5, 2012

no anyone use attr_protected?

@filipeamoreira
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filipeamoreira commented Mar 5, 2012

I really liked this approach. Especially with the added option to do a permission based selection (see follow up comment by @dhh)

@jasonroelofs
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jasonroelofs commented Mar 5, 2012

@wxianfeng attr_protected, IMO, should be removed from ActiveRecord entirely. Blacklisting is almost always a bad idea, and with the nested form parameters stuff Rails already handles, it will hide very devious security holes. Always use attr_accessible to whitelist what people can change.

@larzconwell
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larzconwell commented Mar 5, 2012

@jameskilton Agreed attr_protected will make you assume too much about what attributes aren't available.

@norv
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norv commented Mar 7, 2012

Access control, in particular access from a web form, to the model/database layer, is not a model matter. It's better that attr_accessible needs to be specified from now on, but it's not the end of this issue.

+1 for adnanced, znbailey, original gist.

@atwam
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atwam commented Mar 8, 2012

I've always wondered if rails should add a Form layer, like symfony does.
Having a separate layer that handles validation, nesting, display, assignment security (aware of current user/role) and update of models isn't too bad, and removes a lot of clutter from models...
The way symfony used to do it : http://www.symfony-project.org/forms/1_4/en/01-Form-Creation

@sbeam
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sbeam commented Mar 10, 2012

this is great for a simple case, but sometimes slice isn't enough, e.g. nested attributes, and also date/time fields that come in like "posted_on(1i)"=>"2010", "posted_on(2i)"=>"3", "posted_on(3i)"=>"3"

What about a way to have form_for send to the controller which fields actually exist in the form (how to do this in a tamper-proof fashion is a good question, an encrypted serialized hash of the legitimate keys would be needed) - any params that are not actually in the form_for block would be ignored. Of course there would need to be a way to whitelist other fields in case they were legitimately added client-side via JS.

That way you wouldn't have the model concerned about current user roles and authz, or even the controller. If a field exists in the form, then it seems safe to presume the corresponding param is meant to be changed via that form instance, and v/v.

@bkimble
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bkimble commented Mar 23, 2012

Without the introduction of a deep slice implementation, this approach won't work well with nested attributes/forms. The model will still be the goto spot. A deep slice method in all its recursive glory will be a cpu hog as well :/

@halloffame
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halloffame commented Apr 4, 2012

I'm not sure if slice supports it, but there are ways to support nested attributes using this technique

params[:post].slice(:title, :content, friends: [ :name, { family: [ :name ] }])

source https://github.com/rails/strong_parameters

@JoshCheek
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JoshCheek commented Apr 7, 2012

I'd love to see validations also move out of the model.

@sobrinho
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sobrinho commented Apr 7, 2012

@JoshCheek you can do that using active model ;)

@keithtom
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keithtom commented Dec 11, 2012

Sweet pattern, and I like the simplicity. One thing though:

If someone forgets, or is unaware of the pattern, then you can potentially expose unwanted mass-assignment.

Perhaps, we can combine the strategies so that you can restrict assignment of certain attributes at the model layer, and then have this pattern act more as a 'mark as safe to mass assign'. This seems like it allows controller endpoints to dictate what inputs are acceptable, while letting the model dictate what attributes require additional checks.

As far as actual implementation, it might look more like

@resource.allow_assignment(:password, :password_confirmation)
@resource.update_attributes(params[:resource])

This of course doesn't have to be in a controller. It is really just the idea of forcing developers to explicitly say, "I really want to mass-assign these attributes here".

Thoughts?

@keithtom
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keithtom commented Dec 11, 2012

Ah just read the strong_params gem. nevermind...

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