On Wednesday, March 14, 2012 3:48:53 AM UTC-7, kavkaz wrote:
>
> Get the complicated structure (a three-level hierarchy)
>
> We have the following structure
>
> artists
> :id <--,
> :name |
> | albums_artists
> `---> artist_id
> ,---> album_id
> |
> albums |
> :id <---|
> :label |
> | albums_tracks
> `---> album_id
> ,---> track_id
> tracks |
> :id <---`
> :length
>
>
> One artist, two albums. Each of the album on two tracks.
> Need to get json with the following structure.
>
> [
> {
> "json_class": "Artist",
> "id": 1,
> "name": "Bob",
> "albums": [
> {
> "json_class": "Album",
> "id": 1,
> "label": "Summer",
> "tracks": [
> {
> "json_class": "Track",
> "id": 1,
> "length": 10
> },
> {
> "json_class": "Track",
> "id": 2,
> "length": 20
> }
> ]
> },
> {
> "json_class": "Album",
> "id": 2,
> "label": "Winter",
> "tracks": [
> {
> "json_class": "Track",
> "id": 3,
> "length": 30
> },
> {
> "json_class": "Track",
> "id": 4,
> "length": 40
> }
> ]
> }
> ]
> }
> ]
>
> How to get artists with albums or albums with tracks - it is clear (as
> shown in the script).
> You can tell by what it is to implement without making some "seleŃt",
> if possible, or at least with them.
>
>
> ### script.rb
>
> #!/usr/bin/env ruby
>
> require 'rubygems'
> require 'mysql2'
> require 'sequel'
> require 'logger'
> require 'pp'
>
>
> DB = Sequel.connect( "mysql2://root@localhost/test_3" )
> DB.loggers << Logger.new($stdout)
>
> DB << "drop database test_3"
> DB << "create database test_3"
> DB << "use test_3"
>
>
>
> DB.create_table :artists do
> primary_key :id
> column :name, String
> end
>
>
> DB.create_table :albums do
> primary_key :id
> column :label, String
> end
>
>
> DB.create_table :tracks do
> primary_key :id
> column :length, :integer
> end
>
>
> DB.create_table :albums_artists do
> foreign_key :album_id, :albums
> foreign_key :artist_id, :artists
> end
>
>
> DB.create_table :albums_tracks do
> foreign_key :album_id, :albums
> foreign_key :track_id, :tracks
> end
>
>
> Sequel::Model.plugin :json_serializer
>
> class Artist < Sequel::Model
> many_to_many :albums
> end
>
>
> class Album < Sequel::Model
> many_to_many :artists
> many_to_many :tracks
> end
>
>
> class Track < Sequel::Model
> many_to_many :albums
> end
>
>
> artist = Artist.create(:name => 'Bob')
>
> album1 = Album.create(:label => 'Summer')
> album2 = Album.create(:label => 'Winter')
>
> artist.add_album(album1)
> artist.add_album(album2)
>
> track1 = Track.create(:length => 10)
> track2 = Track.create(:length => 20)
> track3 = Track.create(:length => 30)
> track4 = Track.create(:length => 40)
>
> album1.add_track(track1)
> album1.add_track(track2)
> album2.add_track(track3)
> album2.add_track(track4)
>
>
> ds_artist = Artist.eager_graph(:albums)
> puts ds_artist.to_json(:include => :albums)
>
> ds_albums = Album.eager_graph(:tracks)
> puts ds_albums.to_json(:include => :tracks)
>From reading the module RDoc, I would expect this to do what you want:
ds_artist.to_json(:include=>{:albums=>{:include=>:tracks}})
The specs have similar code, so I'm pretty sure this works.
Thanks,
Jeremy
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