Creating a nested hash from ActiveRecord object in ruby

Question

require "active_record"

ActiveRecord::Base.establish_connection(
  :adapter  => 'mysql2',
  :database => '<db_name>',
  :username => '<username>',
  :password => '<password>',
  :host     => 'localhost')

ActiveRecord::Base.pluralize_table_names = false

class Location < ActiveRecord::Base
    has_many :location_channels
    has_many :channels, :through => :location_channels
end

class Channel < ActiveRecord::Base  
    has_many :location_channels
    has_many :locations, :through => :location_channels
end

class LocationChannel < ActiveRecord::Base  
    belongs_to :location
    belongs_to :channel
end

locations = Location.all

hash = {} # hash initialization

locations.each do |location|
    hash["location"] = location[:name]
        puts "#{location[:name]} has #{location.channels.size} channels:"
            location.channels.each do |channel|
                puts "--> #{channel[:name]}"
            end
        puts
end

puts hash

Final goal is to create one JSON file.

So I decided it'll be easier to create JSON from Hash object.

As in the code above, I'm able to access nested documents via JOIN table called LocationChannel class and I'm trying to figure out how to create a Hash object what will look like:

{ 
  ["location" => "A", "channels" => {"1","2","3"}], 
  ["location" => "B", "channels" => {"1","2"}], 
  ["location" => "C", "channels" => {"4","5","6"}]
}

where "A", "B" and "C" - locations name and "1", "2", etc. - represents channels name.

And the current code prints out only the last record like:

{"location"=>"A"}

Please correct me how should Hash look like if the sample above is wrong.

UPDATE 1

Thanks to @jonsnow for point out the hash format.

Hash format should be:

{ :locations =>
    [
       { name: a, channels: [1,2,3]}, 
       { name: b, channels: [1,2]},
       { name: c, channels: [4,5,6]}
    ]
}

array never store element like this ["location" => "A", "channels" => {"1","2","3"}] . — jon snow
– jon snow, Commented Apr 16, 2015 at 6:25
a Hash can never look like what you are expecting. There are no key => value pairs in your hash — shivam
– shivam, Commented Apr 16, 2015 at 6:26
firs pair is "location" => "A", 2nd pair: does it have to look "channels" => ["1","2","3"] ? — Askar
– Askar, Commented Apr 16, 2015 at 6:31
No oscar, your o/p arrays are in improper format, maybe your o/p should be look like this, { :locations => [{ name: a, channels: [1,2]}, { name: b, channels: [1,2] } ]. — jon snow
– jon snow, Commented Apr 16, 2015 at 6:37

jon snow · Accepted Answer · 2015-04-16 07:08:31Z

1

Solution for your updated hash,

hash = { locations: [] } # hash initialization

locations.each do |location|
  hash[:locations] << { name: location.name,
  channels:  location.channels.pluck(:name) }
end

edited Apr 16, 2015 at 7:08

answered Apr 16, 2015 at 6:51

jon snow

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3 Comments

Askar Over a year ago

in block in <main>': undefined method <<' for nil:NilClass (NoMethodError)

jon snow Over a year ago

Opps, ans is updated. change hash["locations"] to hash[:locations]

Askar Over a year ago

Cool, worked! :) Thanks a lot! I believe many people will benefit from this solution.

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