Rails Select Random Record

Rails—get a random record from db?

You can try following database independent query:

User.find(User.pluck(:id).sample)
[DEBUG]  (36.5ms)  SELECT `users`.`id` FROM `users`
[DEBUG] User Load (0.5ms)  SELECT  `users`.* FROM `users` WHERE `users`.`id` = 58229 LIMIT 1

this one fires two queries but this one is performance efficient as it took only 37ms to get single random user record.

whereas the following query will take around 624.7ms

User.order("RAND()").first
[DEBUG] User Load (624.7ms)  SELECT  `users`.* FROM `users`  ORDER BY RAND() LIMIT 1

I have checked this for 105510 user records.

Random record in ActiveRecord

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.

Rails 3: Get Random Record

Thing.first(:order => "RANDOM()") # For MySQL :order => "RAND()", - thanx, @DanSingerman
# Rails 3
Thing.order("RANDOM()").first

or

Thing.first(:offset => rand(Thing.count))
# Rails 3
Thing.offset(rand(Thing.count)).first

Actually, in Rails 3 all examples will work. But using order RANDOM is quite slow for big tables but more sql-style

UPD. You can use the following trick on an indexed column (PostgreSQL syntax):

select * 
from my_table 
where id >= trunc(
  random() * (select max(id) from my_table) + 1
) 
order by id 
limit 1;

Rails select random record

In Rails 4 I would extend ActiveRecord::Relation:

class ActiveRecord::Relation
  def random
    offset(rand(count))
  end
end

This way you can use scopes:

SomeModel.all.random.first # Return one random record
SomeModel.some_scope.another_scope.random.first

Get random record

You can simply use .shuffle on active record relation which will return you an array.

Post.where(available: 'true', approved:  "true").shuffle.first

Or

Post.where(available: 'true', approved:  "true").sample

Or more efficient way

Post.where(available: 'true', approved:  "true").order("RANDOM()")

Selecting random record in rails

You'll need a separate spot to store the records being displayed already outside of your current process. The process might die or you will have multiple processes running (if it is meant for production purposes, that should definitely be the case).

As opposed to what tadman proposed I wouldn't recommend storing the sequence in the db as this will make adding new records more complicated.

Instead, I would add a simple displayed (boolean) column (or separate table) and rely on what has been proposed in a different thread but flavored to your specific use case. So the query might be like this:

@qotd = Quote.where(displayed: false).order("RAND()").limit(1)

and of course a

@qotd.update_attribute :displayed, true

later on.

The displayed column for all records will have to be reset if no candidate is found. All this, (query, update and reset) should probably happen within a single method.

What's the 'Rails 4 Way' of finding some number of random records?

You'll want to use the order and limit methods instead. You can get rid of the all.

For PostgreSQL and SQLite:

User.order("RANDOM()").limit(10)

Or for MySQL:

User.order("RAND()").limit(10)

how to get a random record from the database in rails

Try this:

# Get 5 random users
@users = User.order('RAND()').limit(5)

Note that the RAND() (MySQL) function is called RANDOM() in PostgreSQL and SQLite.

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