Rails 5: unable to retrieve hash values from parameter

Question

I'm running into a strange issue.

undefined method `values' for #<ActionController::Parameters:0x007fb06f6b2728>

is the error I get, when I assign a variable to a param hash, and try to get it's values.

attributes = params[:line_item][:line_item_attributes_attributes] || {}
attributes.values

the parameter looks like this a hash of hashes:

{"0"=>{"product_attribute_id"=>"4"}, "1"=>{"product_attribute_id"=>"7"}}

now when I do this in console and assign that to a variable attributes it works flawlessly. So I'm struggling to understand what isn't working here - and how to make it work.

Iambic

this is indeed strange. Any object of class ActionController::Parameters should respond to values. What are your ruby and rails versions? Could you add a logger.warn attributes.inspect? – Phelgon

Answer 1

take a look to this. Very weird since ActionController::Parameters is a subclass of Hash, you can convert it directly to a hash using the to_h method on the params hash.

However to_h only will work with whitelisted params, so you can do something like:

permitted = params.require(:line_item).permit(: line_item_attributes_attributes)
attributes = permitted.to_h || {}
attributes.values

But if instead you do not want to whitelist then you just need to use the to_unsafe_h method.

Update

I was very curious about this issue, so I started researching, and now that you clarified that you are using Rails 5, well that's the cause of this issue, as @tillmo said in stable releases of Rails like 4.x, ActionController::Parameters is a subclass of Hash, so it should indeed respond to the values method, however in Rails 5 ActionController::Parameters now returns an Object instead of a Hash

Note: this doesn’t affect accessing the keys in the params hash like params[:id]. You can view the Pull Request that implemented this change.

To access the parameters in the object you can add to_h to the parameters:

params.to_h

If we look at the to_h method in ActionController::Parameters we can see it checks if the parameters are permitted before converting them to a hash.

# actionpack/lib/action_controller/metal/strong_parameters.rb
def to_h
  if permitted?
    @parameters.to_h
  else
    slice(*self.class.always_permitted_parameters).permit!.to_h
  end
end

for example:

def do_something_with_params
  params.slice(:param_1, :param_2)
end

Which would return:

{ :param_1 => "a", :param_2 => "2" }

But now that will return an ActionController::Parameters object.

Calling to_h on this would return an empty hash because param_1 and param_2 aren’t permitted.

To get access to the params from ActionController::Parameters, you need to first permit the params and then call to_h on the object

def do_something_with_params
  params.permit([:param_1, :param_2]).to_h
end

The above would return a hash with the params you just permitted, but if you do not want to permit the params and want to skip that step there is another way using to_unsafe_hash method:

def do_something_with_params
  params.to_unsafe_h.slice(:param_1, :param_2)
end

There is a way of always permit the params from a configuration from application.rb, if you want to always allow certain parameters you can set a configuration option. Note: this will return the hash with string keys, not symbol keys.

#controller and action are parameters that are always permitter by default, but you need to add it in this config.
config.always_permitted_parameters = %w( controller action param_1 param_2)

Now you can access the params like:

def do_something_with_params
  params.slice("param_1", "param_2").to_h
end

Note that now the keys are strings and not symbols.

Hope this helps you to understand the root of your issue.

Source: eileen.codes

Addia

but this class, namely ActionController::Parameters, is a subclass of Hash, and the latter has a method values. – Phelgon

Not actually, that's why there is a to_h method in that class – Addia

try params = ActionController::Parameters.new; params.values to see that you do not need to_h here. – Phelgon

mmm it starts to make sense... lol may be related to rails version? – Addia

I'm running rails 5.0 beta1, tried adding .to_h on the param, but it gives me an empty hash – Iambic

it is because you need to whitelist the params, please read carefully the answer. But you can still use to_unsafe_h and avoid whitelisting – Addia

Please check the answer again, now I found the root of your issue. Hope it helps you – Addia

Answer 2

Since Rails 5, params are of class 'ActionController::Parameters'

If you do params.to_h you will get the following error.

*** ActionController::UnfilteredParameters Exception: unable to convert 
unpermitted parameters to hash

You can do as follows to permit all the params and get as Hash format:

parameters = params.permit(params.keys).to_h

"But beware of using this! You are permitting all the params which may include unknown params that can harm your code."

Rufina

Answer 3

I think what's happening is the following:

In a console you are working with a simple hash called attributes. As a hash the attributes parameter in the console has a valid instance method called values.

In your rails app the params hash is not a simple hash any more. It is an instance of the ActionController::Parameters class. As an instance of that class it does not have an instance method called values, but it does have an instance method called to_h & to_unsafe_h, which would accomplish your goals. After calling to_h on your parameters you can call the values method.

Disassemble

but the class ActionController::Parameters, is a subclass of Hash, and the latter has a method values. – Phelgon

More specifically, try in a console params = ActionController::Parameters.new({line_item: ActionController::Parameters.new({line_item_attributes_attributes: ActionController::Parameters.new})}); attributes = params[:line_item][:line_item_attributes_attributes] || {}; puts attributes.class; attributes.values – Phelgon

true... you can also simply run ActionController::Parameters.method_defined? :values and you'll see that values is a valid method... now I'm stumped – Disassemble

@Phelgon diving into the Ruby though you can try this with your params variable: params.kind_of? Hash #=> true, but then try params.instance_of? Hash #=> false So params is a kind of hash, but not an instance of hash... why would that be? – Disassemble

Looking in Rails 5, Parameters no longer inherits from Hash (via HashWithIndifferentAccess), but they did add :values as a delegate method, so it should still work... Here is the Rails 5 code vs. the Rails 4 code – Disassemble

I'm indeed using Rails 5, however when I do attributes = params[:line_item][:line_item_attributes_attributes].to_h it becomes an empty hash. – Iambic

You have to call to_h on the safe version of the params, i.e. my_params = params.permit(:line_item).require(:product_attribute_id), basically wherever you whitelisted your params in the controller... otherwise you have to call to_unsafe_h on params... or you can probably run this: params.permit!.to_h, but that will permanently de-whitelist your params hash, which you shouldn't want... better to work with a safe version of the params hash – Disassemble

And... :values should still work since it was added as a delegate method in Rails 5. – Disassemble

Answer 4

Word to the wise: if you're using link_to_sorted from the sorted gem it breaks views in Rails 5.

Anya