如何在后端的 Rails 上使用 Ruby 在发布请求中访问嵌套的 json 参数

Question

I need to access the json parameters from a form post request in a Ruby on Rails backend controller. I need to access a model object (carrier-type), in order to get the id. However, I keep getting the following error. Can anyone advise how I would access this data?

Error:

undefined method `[]' for nil:NilClass excluded from capture: DSN not set
app_1         |
app_1         | NoMethodError (undefined method `[]' for nil:NilClass):

Sample Json Data:

{"_jsonapi"=>
    {"data"=>
        {"attributes"=> {"device"=>mobile},
         "relationships"=>
            {"carrier-type"=>{"data"=>{"id"="1}}}
            }
        }
    }
}

Access Attempt:

I have tried the following

@myParams = params[:_jsonapi];
Rails.logger.info("STARTTIME PARAMS: #{@myParams}")

Answer 1

You must be trying to access the id in the following way

params["_jsonapi"]["data"]["relationships"]["carrier-type"]["data"]["id"]

this can throw you an error if any of the previous key will not be there in your JSON.

ie

params["_jsonapi"]["key_that_is_not_present"]["relationships"]["carrier-type"]["data"]["id"]

will through error like:

NoMethodError (undefined method `[]' for nil:NilClass)

I would suggest you to use dig here.

params.dig("_jsonapi", "data", "relationships", "carrier-type", "data", "id")

in this way you will not get an error but if any key is not present you will get nil ie

params.dig("_jsonapi", "random_key")

will return nil