Storing arrays in database using ActiveRecord

Question

I am on rails 2.3.8 & I am using mysql as db adapter. I want to store arrays in my database. After searching I could come up with this very useful article.

Now I need to use GUI for input & not only server console. So say I have a text field called nums which logically should have int array. What should be the format of nums so that it becomes easy to retrieve & store the array out of that string ?

Answer 1

If you use serialize then you shouldn't have to worry about how the data is stored within the text field, although it's actually YAML.

serialize is documented in the Rails/ActiveRecord API (scroll down to the section headed "Saving arrays, hashes, and other non-mappable objects in text columns")

For display, you need a format that is understandable to users and that can be easily converted back into an array in your code. Comma- or space-delimited?

Formatting for output:

delim = ',' # or ' ' for spaces, or whatever you choose array.join(delim) 

Converting back into an array might work as follows:

num_array = nums.split(delim).map(&:to_i) # or to_f if not integers 

or perhaps using String#scan?

num_array = nums.scan(/\d+/).map(&:to_i) # for positive integers 

Answer 2

If you're using postgres and rails 4, now you have a better native option.

# db/migrate/20140207133952_create_books.rb create_table :books do |t|   t.string 'title'   t.string 'tags', array: true   t.integer 'ratings', array: true end add_index :books, :tags, using: 'gin' add_index :books, :ratings, using: 'gin'  # app/models/book.rb class Book < ActiveRecord::Base end  # Usage Book.create title: "Brave New World",             tags: ["fantasy", "fiction"],             ratings: [4, 5]  ## Books for a single tag Book.where("'fantasy' = ANY (tags)")  ## Books for multiple tags Book.where("tags @> ARRAY[?]::varchar[]", ["fantasy", "fiction"])  ## Books with 3 or more ratings Book.where("array_length(ratings, 1) >= 3") 

http://edgeguides.rubyonrails.org/active_record_postgresql.html