Formatting data before ActiveRecord insertion


Sorry if this is a noob question.

I’m trying to store a hash of values (a user’s music collection) into a single database record without having to have a separate row in the db for each music track the user has in his collection.

e.g. User 9

{ 12319 => “Artist X: Song Name 1”,

12198 => “Artist X: Song Name 2”,

19180 => “Artist Y: Song Name 3”,

92810 => “Artist Z: Song Name 4” }

I’m going serialize this hash with serialize: and store it in a text field.

I’d like the create, update_attributes, save, etc. methods that could potentially write to this field to create this hash structure (if none exists), add to the hash structure, or remove an entity from this structure automatically without someone using my model having to manually getting the record, read the hash and adding/deleting from the hash.

I’ve thought about the following as options:

  1. attr_protected :music_tracks

and write a custom accessor to manipulate the hash.

  1. overriding the create, update_attributes, save etc. methods of ActiveRecord to manipulate the hash.

Am I going about this wrong, or any suggestions on the 2 options?



Not answering the question, I know, but I would advise against doing
it this way. Have a tracks table, User has_many tracks, Track
belongs_to user. Then for a user his tracks are
and for each track the artist and name are track.artist and
You will not have to write all the code you are struggling with, Rails
will do it for you. The less code you have to write the better.


You can manipulate data before saving it

class User
  before_save :do_something

  def do_something
    // process music_tracks here

PS: I do not know the purpose of your project, but in general, having
a table of songs referred by id seems a better option to me.

Song 1 => { band => "Kiss", "title" => "Strutter" }
User 1 => [1, 1, 1]
User 2 => [1, 1, 1]
User 3 => [1, 1, 1]

In your case, you will get multiple copies of bloated data spread all
over DB if many users listen to the same song over and over again.

User 1 => { 1 => "Kiss: Strutter",
            2 => "Kiss: Strutter",
            3 => "Kiss: Strutter" }
User 2 => { 1 => "Kiss: Strutter",
            2 => "Kiss: Strutter",
            3 => "Kiss: Strutter" }
User 3 => { 1 => "Kiss: Strutter",
            2 => "Kiss: Strutter",
            3 => "Kiss: Strutter" }