How to store each key or element from array to database in rails

Question

I'm stuck on trying to store keys or elements from a returned array into the database. It looks something like:

{"id"=>"28898790358_10152709083080359",
 "from"=>{"category"=>"Tv channel",
          "category_list"=>[{"id"=>"169056916473899",
                             "name"=>"Broadcasting & Media Production"}],
          "name"=>"WGRZ - Channel 2, Buffalo",
          "id"=>"28898790358"} 

I'm trying to grab stuff like 'id', 'category_list', all of their values and store it into a column of a database table.

I've got it before but this time only certain values get in and usually I get an error:

undefined method[]

Answer 1

You're getting the undefined method [] error when you try to use the [] method on a class that doesn't have that method defined. My guess is that you are running into this problem while parsing the above hash (e.g. calling [] on Nil Class, and getting the error undefined method [] for nil:NilClass).

Long Story Short: You need to parse the JSON and save the items you need to the appropriate spots in the database

I'm a little unclear about the example you gave, so I'll try to use a simplified one.

Suppose you are querying for a TvShow, which belongs_to a TvChannel. TvChannel also has_many_and_belongs_to a certain Category. So perhaps this query you are doing returns the TvShow, along with the TvChannel and Category to which the TvShow belongs. Suppose you get back something like the json below:

    json_response = { 'name': 'Desperate Housewives',
                      'id': '12345-67890',
                      'tvChannel': {
                                     'name': 'ABC',
                                     'id': '123-456-789',
                                     'categories': [
                                                     { 'name': 'Comedy',
                                                       'id': '000-000'   },
                                                     { 'name': 'Drama',
                                                       'id': '111-111'   }
                                                    ]
                                   }
                     }

So now you want to save the TvShow Desperate Housewives to the TvChannel ABC, and save ABC to the Categories Comedy and Drama. This is how I would go about parsing:

    new_show = TvShow.new
    new_show.name = json_response["name"]
    new_show.external_id = json_response["id"] # assuming you want to save their identifier

    channel = TvChannel.find_or_create_by(:name, json_response["tvChannel"]["name"]) # you might want to do this by the id, but it's up to you.
    new_show.tv_channel = channel  # this saves the TvChannel's ID to the new_show's tv_channel_id foreign key field
    new_show.save  # save your new TV Show to the database, with the name, id, and tv_channel_id.

    # Next we parse the "categories" part of the JSON, finding each Category by name (creating a new Category if one doesn't exist by that name), 
    # And then adding our TvChannel to that Category
    json_response["tvChannel"]["categories"].each do |category|
      c = Category.find_or_create_by(:name, category["name'])
      channel.categories << c
      channel.save
    end

I hoped this helped show you how to parse JSON responses, and how to use ActiveRecord to create or find instances in your database. It is useful to store the JSON response to a variable (json_response in my example above), for easier parsing.

Let me know if I can clarify anything!