Accessing first element of array in rails

Question

I am getting below json from backend.

{ drug:
  {

    "id": "580f323ee4b06ffee69041a1",
    "direction": [
        {
            "direction": "test",
            "discarded": false
        }
    ]
  }
}

I dont want direction as array. I want it as object so I wrote method drug_format to parse json

My ruby on rails code for parsing is as follows :

def drug_format drug
{
  id: drug[:id],
  direction: drug[:direction][0],
}
end

Now when I am trying to run my code I am getting following error.

NoMethodError (undefined method `[]' for nil:NilClass):
    app/controllers/drugs_controller.rb:280:in `drug_format'
    app/controllers/drugs_controller.rb:15:in `block in index'
    app/controllers/drugs_controller.rb:14:in `each'
    app/controllers/drugs_controller.rb:14:in `index'

What can be the issue?

What is drug and what does drug[:id] or drug[:direction] return? — Stefan
– Stefan, Commented Oct 26, 2016 at 10:59
drug[:id] returns string and drug[:direction] returns array of object. I want to access first object of array. — Parag Pakhale
– Parag Pakhale, Commented Oct 26, 2016 at 11:08
If drug is a hash and drug[:direction] returns an array, then neither drug[:id] nor drug[:direction][0] would raise that error. — Stefan
– Stefan, Commented Oct 26, 2016 at 11:19

gabrielhilal · Accepted Answer · 2016-10-26 12:01:12Z

2

the json keys are strings and not symbols, so you need something like:

def drug_format drug
  {
    id: drug['id'],
    direction: drug['direction'][0]
  }
end

or you can use with_indifferent_access

console output:

params = {
 'drug' => {
    "id" => "580f323ee4b06ffee69041a1",
    "direction" => [
        {
            "direction" => "test",
            "discarded" => false
        }
    ]
  }
}
=> {"drug"=>{"id"=>"580f323ee4b06ffee69041a1", "direction"=>[{"direction"=>"test", "discarded"=>false}]}}

params[:drug]
=> nil

params['drug']
=> {"id"=>"580f323ee4b06ffee69041a1", "direction"=>[{"direction"=>"test", "discarded"=>false}]}

def drug_format(drug)
  {
    id: drug['id'],
    direction: drug['direction'][0]
  }
end
=> :drug_format

drug_format(params[:drug])
=> NoMethodError: undefined method `[]' for nil:NilClass

drug_format(params['drug'])
=> {:id=>"580f323ee4b06ffee69041a1", :direction=>{"direction"=>"test", "discarded"=>false}}

edited Oct 26, 2016 at 12:01

answered Oct 26, 2016 at 10:34

gabrielhilal

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8 Comments

gabrielhilal Over a year ago

it might an issue accessing the drug param... please note my edited answer

Edvaldo Silva de Almeida Jr Over a year ago

GEnerated JSON is not correct. Take away this comma in direction: drug[:direction][0],, because there is no reason for it to be there. A comma says there will be another key after that element.

Deepak Mahakale Over a year ago

@EddeAlmeida that doesn't matter in ruby

Deepak Mahakale Over a year ago

@EddeAlmeida just checked your profile, correct if I said something wrong.. You shoud have digged ruby a lot ;)

Deepak Mahakale Over a year ago

Yes I did and the , is handeled so {a: 'abc', } dosn't throw any errors

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