X-Combinator

Say you have the following data model

and you want to execute a single query that returns all the data at once within the ActiveRecord tables, with the proper rails associations between them. Wouldn’t it be nice if you could do something like

? Though this is not even valid ruby code, it actually comes very close to what you can do in Ruby on Rails. To get this right, let’s take a closer look at the rails associations within the class definitions:

Let’s try the rails code again, putting an ’s’ after the :c and :e as required by rails in order to denote they are “many”-type associations:

That’s closer, but still not valid ruby code. To fix that, think of the => operator as being right-associative, and instead of putting in parentheses (), put in curly braces {} in order to create nested hashes:

That’s it! Looking in the logs, we see that this only produced a single query, with all the desired SQL joins:

A Load Including Associations (0.001088) SELECT `as`.`id` AS t0_r0, `as`.`b_id` AS t0_r1, `bs`.`id` AS t1_r0, `cs`.`id` AS t2_r0, `cs`.`b_id` AS t2_r1, `cs`.`d_id` AS t2_r2, `ds`.`id` AS t3_r0, `ds`.`c_id` AS t3_r1, `es`.`id` AS t4_r0 FROM `as` LEFT OUTER JOIN `bs` ON `bs`.id = `as`.b_id LEFT OUTER JOIN `cs` ON cs.b_id = bs.id LEFT OUTER JOIN `ds` ON ds.c_id = cs.id LEFT OUTER JOIN `ds_es` ON `ds_es`.d_id = `ds`.id LEFT OUTER JOIN `es` ON `es`.id = `ds_es`.e_id

With this tool in mind, you can use this in any ActiveRecord function that accepts the :include option to reduce the number of times the rails app hits the database, and ultimately speed up your rails application.