Rails has_many association count child rows

Question

What is the \"rails way\" to efficiently grab all rows of a parent table along with a count of the number of children each row has?

I don\'t want to use counte

Answer 1

This activerecord call should do what you want:

Article.find(:all, :select => 'articles.*, count(posts.id) as post_count',
             :joins => 'left outer join posts on posts.article_id = articles.id',
             :group => 'articles.id'
            )

This will return a list of article objects, each of which has the method post_count on it that contains the number of posts on the article as a string.

The method executes sql similar to the following:

SELECT articles.*, count(posts.id) AS post_count
FROM `articles`
LEFT OUTER JOIN posts ON posts.article_id = articles.id
GROUP BY articles.id

If you're curious, this is a sample of the MySQL results you might see from running such a query:

+----+----------------+------------+
| id | text           | post_count |
+----+----------------+------------+
|  1 | TEXT TEXT TEXT |          1 |
|  2 | TEXT TEXT TEXT |          3 |
|  3 | TEXT TEXT TEXT |          0 |
+----+----------------+------------+