Find all users unless has_many matches a specific date

finder.rb

User

has_many :bookings

| id  | name  |
---------------
| 1   | amy   |
| 2   | jack  |


Booking

belongs_to :user

| id  |     date    | user_id |
-------------------------------
| 1   | 2014-01-01  |       1 |
| 2   | 2014-01-02  |       2 |
| 3   | 2014-01-03  |       1 |
| 4   | 2014-01-04  |       2 |
| 5   | 2014-01-05  |       1 |


specific_date = '2014-01-03'

# I've tried a whole bunch of combinations of the following:

User.joins(:bookings).where('bookings.date = ?', specific_date).having('count(*) != 1')

# Query should only return User 'jack' because 'amy' has an associated booking with date = specific_date

# The following in plain mysql works for what I want, but I cannot find a solution to write this activerecord query:

HAVING (SELECT COUNT(*) FROM bookings WHERE bookings.date = '2014-01-03' AND bookings.user_id = users.id) != 1

# I cannot use straight sql because "#{specific_date}" opens up sql injection... and it's just ugly

hmmm, been looking into it. Haven't been able to find a way, other than having two queries, finding the booked vendors first, then getting the users not in the result... Too expensive?