Rails - how to fetch random records from an object?

I am doing something like this:

data = Model.where('something="something"')
random_data = data.rand(100..200)

returns:

NoMethodError (private method `rand' called for #<User::ActiveRecord_Relation:0x007fbab27d7ea8>):

Once I get this random data, I need to iterate through that data, like this:

random_data.each do |rd|
  ...

I know there's a way to fetch random data in MySQL, but I need to pick the random data like 400 times, so I think to load data once from database and 400 times to pick random number is more efficient than to run the query 400 times on MySQL.

But - how to get rid of that error?

NoMethodError (private method `rand' called for #<User::ActiveRecord_Relation:0x007fbab27d7ea8>):

Thank you in advance