A simple post on exposing other attributes when returning a json representation of a model instance.

Sometimes when querying information, we also want to display associations' information - instead of knowing only the foreign key id.

Disclaimer

Of course there could be other time saving or more efficient way of querying, like using Graph API or storing constant data in some other storage.

An example

Lets say our Ruby on Rails project has a model called Book.rb and Author.rb.

Author has many books and book belongs to an Author, hence book will have an author_id attribute, which most of the time is just a bigint.

For my case, I chose to expose the author name as part of the model.

# Book.rb
belongs_to :author

def author_name
  Author.find(author_id).name
end

def as_json(options = {})
  json = super(options)
  json[:author_name] = author_name
  json
end

Override the as_json method

1. Initialise json hash with current model
2. Add author_name key, and value to hash
3. Return final json hash

Tada! Simple :)