Ruby on Rails: Get specific substring out of string - ruby-on-rails

Question

a little help with getting data out of a string.
Assuming I executed a sql query and now have a string(which set as hash on db):
"{\"users_associated\":{\"User:4\":6,\"User:22\":28,\"User:30\":36}}"
(Which stands for User:ID : User.display_id)
How can I get a substring the includes all users ids or all their display ids, so I'll have something like 4,22,30 or 6,22,36)?
Thanks!

Answer 1

It's common for data systems to return data in a serialized form, i.e. using data types that facilitate transmission of data. One of these serializable data types is String, which is how your JSON data object has been received.
The first step would be to de-serialize (or parse) this String into a Hash object using JSON.parse and tease out just the data value for key "users_associated".
your_string = "{\"users_associated\":{\"User:4\":6,\"User:22\":28,\"User:30\":36}}"
hash = JSON.parse(your_string)
data = hash["users_associated"]
#=> {"User:4":6, "User:22": 28, "User:30": 36}
Hash#keys gives you an array of a hash's keys.
Hash#values gives you an array of a hash's data values.
keys = data.keys
#=> ["User:4", "User:22", "User:30"]
values = data.values
#=> [6, 28, 36]
Array#join lets you string together the contents of an array with a defined separator, , in this case.
display_ids = keys.join(',')
#=> "6,28,36"
For the User IDs, you could Array#map every element of the values array to replace every string occurrence of "User:" with "", using String#gsub.
user_ids = values.map{|user_id| user_id.gsub("User:", "")}
#=> ["4", "22", "30"]
Then, in a similar way to display_ids, we can Array#join the contents of the user_ids array to a single string.
user_ids = user_ids.join(",")
#=> "4,22,30"

Answer 2

You can create two helper methods. I'm leaving return values as arrays because I assume you would need to iterate on them at some point and also converting the user id's to integers.
def extract_display_ids(json)
json['users_associated'].values
end
def extract_user_ids(some_data)
json['users_associated'].keys.map{ |key| key.split(':').last.to_i }
end
some_data = JSON.parse("{\"users_associated\":{\"User:4\":6,\"User:22\":28,\"User:30\":36}}")
extract_display_ids(some_data)
#=> [6, 28, 36]
extract_user_ids(some_data)
#=> [4, 22, 30]
If possible though, I would recommend trying to get a better data format:
{ users_associated:
[{ user_id : 4, display_id:6 }, { user_id : 4, display_id:6 }]
}

Answer 3

I wrote class for this. If you want, you can add it to your project and use it as follows:
require 'json'
class UserSubstringExtractor
def initialize(user_json_data)
#user_json_data = user_json_data
end
def display_ids
user_data.dig('users_associated').values
end
def user_ids
user_data.dig('users_associated').keys.map { |u| u.split(':').last.to_i }
end
private
def user_data
JSON.parse(#user_json_data)
end
end
user_json_data = '{"users_associated":{"User:4":6,"User:22":28,"User:30":36}}'
extractor = UserSubstringExtractor.new(user_json_data)
p extractor.display_ids
#=> [6, 28, 36]
p extractor.user_ids
#=> [4, 22, 30]