Storing arrays in database : JSON vs. serialized array [closed]

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With ruby-on-rails, I want to store an array of 3 elements: the last 3 comments of a post. I know I could join the Comment table to the Post one, but I would avoid to do this heavy request for scaling purposes.

So I was wondering what was the best way to store those 3 elements, as I would like to update them easily every time a new comment is made: remove the last comment and add the new one.

What is the correct way to do this ? Store it in a serialized array or in a JSON object ?

I'm using postgres : you recommend using their array column type ? — titibouboul
– titibouboul, Commented Jan 23, 2014 at 15:22
Obviously. Why would you want to mess with JSON, if you have arrays. — Sergio Tulentsev
– Sergio Tulentsev, Commented Jan 23, 2014 at 15:23
I'm using Rails 3.2 and it doesn't seem to support that function of PG — titibouboul
– titibouboul, Commented Jan 23, 2014 at 15:27
@titibouboul It is a good practice to add your stack details especially rails and ruby version in question by default. It saves a lot of your time and experienced people can answer better and faster (: — ARK
– ARK, Commented Dec 3, 2019 at 13:22

Dennis · Accepted Answer · 2014-10-02 14:31:45Z

96

You can store Arrays and Hashes using ActiveRecord's serialize declaration:

class Comment < ActiveRecord::Base
  serialize :stuff
end

comment = Comment.new  # stuff: nil
comment.stuff = ['some', 'stuff', 'as array']
comment.save
comment.stuff # => ['some', 'stuff', 'as array']

You can specify the class name that the object type should equal to (in this case Array). This is more explicit and a bit safer. You also won't have to create the array when you assign the first value, since you'll be able to append to the existing (empty) array.

class Comment < ActiveRecord::Base
  serialize :stuff, Array
end

comment = Comment.new  # stuff: []
comment.stuff << 'some' << 'stuff' << 'as array'

You can even use a neater version called store: http://api.rubyonrails.org/classes/ActiveRecord/Store.html

This should handle your use case using a built in method.

edited Oct 2, 2014 at 14:31

Dennis

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answered Jan 23, 2014 at 17:29

DiegoSalazar

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2 Comments

Dennis Over a year ago

I'm guessing the stuff field would be of type string when stubbing out the model?

Dennis Over a year ago

To answer my own question, a type of string or text would work for this example, though text should be preferred since you don't want to accidentally run into the max length limit.

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