Parse JSON with an array in Rails

Question

I have the following JSON string returned by a remote server:

{
  "users": [
    {
      "user_id": 1,
      "name": "Chris Rivers",
    },
    {
      "user_id": 3,
      "name": "Peter Curley",
    }
  ]
}

I'd like to iterate the users.

ActiveSupport::JSON.decode(response.body)["users"].each do |user|
    puts user["name"]
end

As far as I understand, the problem is: ruby doesn't recognize ActiveSupport::JSON.decode(response.body)["users"] as an array, and thus puts returns me only the first user.

How do I solve that problem?

deefour · Accepted Answer · 2013-03-27 22:06:45Z

10

What you have pasted is not valid JSON. The trailing comma after on each "name" is a problem

"name": "Chris Rivers",

You'll get a LoadError trying to decode this with ActiveSupport::JSON.decode

MultiJson::LoadError: 399: unexpected token at '{"user_id": 1,"name": "Chris Rivers",},{"user_id": 3,"name": "Peter Curley",}]}'

If we clean up the JSON, turning it into something ActiveSupport::JSON.decode can understand

"{\"users\": [{\"user_id\": 1,\"name\": \"Chris Rivers\"},{\"user_id\": 3,\"name\": \"Peter Curley\"}]}"

you'll see there is no issue iterating over each object in "users" (x below is the above JSON string)

[8] pry(main)> ActiveSupport::JSON.decode(x)["users"].map { |user| user["name"] }
=> ["Chris Rivers", "Peter Curley"]

answered Mar 27, 2013 at 22:06

deefour

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Dan Wich · Accepted Answer · 2013-03-27 22:07:31Z

8

Does your source data actually have the trailing commas after each user's name? I get a parse error for that, but your code works as you want it to if I remove them:

json = '{ "users": [ { "user_id": 1, "name": "Chris Rivers" }, { "user_id": 3, "name": "Peter Curley" } ]}'
ActiveSupport::JSON.decode(json)["users"].each do |user|
   puts user["name"]
end

answered Mar 27, 2013 at 22:07

Dan Wich

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Comments

Dave Newton · Accepted Answer · 2013-03-27 22:55:43Z

6

The problem isn't not recognizing the array, it's the trailing commas after the "name" elements.

Removing those allows JSON parsing to proceed normally:

pry(main)> ActiveSupport::JSON.decode(s)["users"]
=> [{"user_id" => 1, "name" => "Chris Rivers"},
    {"user_id" => 3, "name" => "Peter Curley"}]

edited Mar 27, 2013 at 22:55

answered Mar 27, 2013 at 22:06

Dave Newton

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