Question

I am using Ruby on Rails 3.0.7 and I would like to improve the following code:

@user.article_relationships.select(:category_id).map(&:category_id)

Where:

• @user is an instance of a User class
• article_relationships is the method “gained” by an User Active Record Association with the Article class
• :category_id is an attribute of each article_relationships (that is, a database table column of article_relationships)

The output of the above code is something like this:

# Those are all 'category_id' values present in the 'article_relationships' array
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]

There is a way to improve that code for performance purposes (mostly for the select(:category_id).map(&:category_id) part)? That is, there is a “direct” way to retrieve category_id data?

Answer 1

In a word… no. There’s not a more “direct” way to access the category_ids. Some notes though:

• You don’t have to do .select(:category_id). Unless article records contain lots of data, the performance increase would be negligible. @user.article_relationships.map(&:category_id) should do.

• More than anything, the largest performance boost you could get here is by indexing the user_id column in the articles table. This can easily be done in a migration: add_index :articles, :user_id.