has_many through association dependent destroy under condition of who called destroy

Question

Is there a way to check, within a `before_destroy` hook, what object (class) called `destroy`? In the following example, when a `patient` is destroyed, so are their `appointments` (which is what I want); however I don't want to allow a `physician` to be destroyed if there are any `appointments` associated with that `physician`. Again, is there a way to do such a check in the `before_destory` callback? If not, is there any other way to accomplish this "destruction check" based on the "direction" of the call (i.e. based on who called)? ``` class Physician < ActiveRecord::Base has_many :appointments, dependent: :destroy has_many :patients, through: :appointments end class Patient < ActiveRecord::Base has_many :appointments, dependent: :destroy has_many :physicians, through: :appointments end class Appointment < ActiveRecord::Base belongs_to :patient belongs_to :physician before_destroy :ensure_not_referenced_by_anything_important private def ensure_not_referenced_by_anything_important un…

Accepted Answer

Just say:

```
class Physician < ActiveRecord::Base
  has_many :appointments, dependent: :restrict_with_exception
  has_many :patients, through: :appointments
end
```

Note the `dependent: :restrict_with_exception`. This will cause Active Record to refuse to destroy any Physician records that have associated Appointment records.

See the API docs and the association basics guide.

has_many through association dependent destroy under condition of who called destroy

Solution

Problem