ActiveRecord appends 'AND (1=0)' to end of queries

Question

I've been playing around in the rails console trying to get things to work, and I notice that one of my queries keeps returning nil when it shouldn't. Upon looking at the generated SQL query I notice that it has AND (1=0) appended to it each time. This is kind of annoying, and I'm not sure why it's doing this.

Note: Using the actable gem.

Steps to reproduce:

(After connecting to tables in rails console)

2.1.2 :xxxx > @parent = Parent.take Parent Load (38.1ms)  SELECT  `parents`.* FROM `parents`  LIMIT 1  => #<Parent id: 37, ...>  2.1.2 :xxxx > @child = Child.where(id: @parent.actable_id) SQL (0.7ms)  SELECT `childs`.`id` AS t0_r0, `childs`.`attribute` AS t0_r1, FROM `childs` ... LEFT OUTER JOIN `parents` ON `parents`.`actable_id` = `childs`.`id` AND `parents`.`actable_type` = 'child type' WHERE `childs`.`id` = 20 AND (1=0)  => #<ActiveRecord::Relation []> 

Why is this happening? How do I make it stop?

Answer 1

Rails will generate SQL like AND (1=0) when you query for a column whose value is in an empty array:

Child.where(id: []) 

Intuitively, you'd expect that to generate SQL like SELECT * FROM children WHERE id IN (), but () isn't actually valid SQL. Since no rows will match that query, though, Rails works around this by generating an equivalent query that also returns no rows:

SELECT * FROM children WHERE 1=0;