Rails 6 select 随机 ActiveRecord object 每个类别

Question

I've got TestQuestion model where I store survey questions with predefined and hardcoded categories:

CATEGORIES = %w[Q1 Q2 Q3 Q4]

I want to present to user randomly selected one published question from each category of questions. I was trying something like:

CATEGORIES.each { |c| TestQuestion.where(category: c).random }

But I'm getting an error: NoMethodError (undefined method random' for <TestQuestion::ActiveRecord_Relation:0x00007f091cf1ac08>)

Besides I think it's a smelly code. Is there any better way to do that?

Answer 1

there is no random function but you can do (depending on your database)

Postgresql or SQLite:

TestQuestion.where(category: c).order('RANDOM()').first

MySQL:

TestQuestion.where(category: c).order('RAND()').first

you can also use Arel

TestQuestion.where(category: c).order(Arel.sql('RANDOM()')).first

note: that if your DB is large and there is a performance issue you might want to limit(1) then first

you are also using each. which will return the original object you are iterating through, you need to switch to map.