Random record in ActiveRecord

Question

I'm in need of getting a random record from a table via ActiveRecord. I've followed the example from Jamis Buck from 2006.

However, I've also come across another way via a Google search (can't attribute with a link due to new user restrictions):

 rand_id = rand(Model.count)  rand_record = Model.first(:conditions => ["id >= ?", rand_id]) 

I'm curious how others on here have done it or if anyone knows what way would be more efficient.

Answer 1

Rails 6

As stated by Jason in the comments, in Rails 6, non-attribute arguments are not allowed. You must wrap the value in an Arel.sql() statement.

Model.order(Arel.sql('RANDOM()')).first 

Rails 5, 4

In Rails 4 and 5, using Postgresql or SQLite, using RANDOM():

Model.order('RANDOM()').first 

Presumably the same would work for MySQL with RAND()

Model.order('RAND()').first 

This is about 2.5 times faster than the approach in the accepted answer.

Caveat: This is slow for large datasets with millions of records, so you might want to add a limit clause.

Answer 2

I haven't found an ideal way to do this without at least two queries.

The following uses a randomly generated number (up to the current record count) as an offset.

offset = rand(Model.count)  # Rails 4 rand_record = Model.offset(offset).first  # Rails 3 rand_record = Model.first(:offset => offset) 

To be honest, I've just been using ORDER BY RAND() or RANDOM() (depending on the database). It's not a performance issue if you don't have a performance issue.