I have a weird relationship that needs to be maintained for legacy processes. I'm trying to figure out how to create the relationship given the new model association. New Relationship Setup Machine has_many MachineReadings has_many Disks has_many DiskReadings Old Relationship Setup Machine has_many MachineReadings has_many DiskReadings has_many Disks The problem is data will come in on the Machine model as nested attributes using the new relationship setup. I need to update the machine_reading_id in the DiskReading model so the old association can continue to be used. I tried doing this via an after_save hook that would traverse back up to the machine and then down to the readings to get the machine_reading.id so I could populate the DiskReading model. However, the associations aren't being saved in the order I would expect. They are saving the Disks & DiskReadings before saving the MachineReadings. So when I go after the machine_reading.id it hasn't been written and thus I am unable to get access to it. For example: #machine_disk_reading.rb after_save :build_old_relationship def build_old_relationship self.machine_reading_id = self.disk.machine.readings.find_by_date_time(self.date_time).id end