How to validate date attributes in rails(custom_validations)?

See more:

Ruby

database

model

Rails

I have two models.

models/Resident.rb : has_many: leaves

models/leave.rb: belongs_to: resident

Now what I want to validate leave model attributes before they get created..

leave.rb attributes : start_date,end_date,destination

here is my leave model:

class Leave < ActiveRecord::Base
  belongs_to :resident
  validates :destination,presence:true
  validates :end_date,presence: true
  validates :start_date,presence: true
  before_create :check_correct_leave

  private

  def check_correct_leave

   if resident.hostel.hostel=='J'
     (self.end_date - self.start_date).to_i == 4 ||  (self.end_date - self.start_date).to_i == 5

   else
     errors.add(:start_date, "Leave are granted only 4 or 5 days")
   end

  end

end

I want check_correct_leave method to also check if the resident already have a leave (stored in a leave model) of that a month (month means jan,feb,etc) then it should generate an error that:

You cant mark leave cause you have already marked leave for this month and model should not store that leave.
Thanks

What I have tried:

I tried this
def has_leave_for_the_same_month?
resident.leaves.any? do |other_leave|
other_leave.start_date.month == leave.start_date.month
end
end

errors.add(...) if has_leave_for_the_same_month?
not working