I have two models/tables in my Rails application: discussions and comments. Each discussion has_many comments, and each comment belongs_to a discussion. My discussions table also includes a first_comment_id column and last_comment_id column for convenience and speed. I want to be able to call discussion.last_comment for the last comment model, but the following (in my discussion model) isn’t working to make this happen:
has_one :first_comment, :class_name => "Comment"
has_one :last_comment, :class_name => "Comment"
When I call discussion.last_comment, the following SQL is run:
SELECT * FROM `comments` WHERE (`comments`.discussion_id = 1) LIMIT 1
It’s using the discussions.id column to join against comments.discussion_id, when I want it to join discussions.last_comment_id against comments.id.
Am I using the wrong type of association here? Thanks for your help!
Try a
belongs_to, rather than ahas_one.The naming might be odd, but the difference between the two is really just about which of the tables holds the foreign key column.