How to make a has_one through has_many association?

Merey Nurlan 0
Viewed 38

Context: I have 2 models ClinicalSystem and TemplateMessage

My goal: is to have ClinicalSystem with many TemplateMessage but also have multiple has_one realtion with TemplateMessage with different namings. e.g:

clinical_system.tempalte_messages, clinical_system.reschedule_template_message, clinical_system.cancellation_template_message.

How do I structure my associations to achieve that ? I have tried has_many: through but it failed.

activerecord ruby ruby-on-rails
2 Answers

You can define the main has_many association and the has_one associations separately like below:

class ClinicalSystem
  has_many :tempalte_messages
  has_one :reschedule_template_message, -> { CONDITION_FOR_RESCHEDULE }, class_name: TemplateMessage.name
  has_one :cancellation_template_message, -> { CONDITION_FOR_CANCELLATION }, class_name: TemplateMessage.name
end
userLZUS0

You can achieve that using foreign_key and class_name

class ClinicalSystem
  has_many :tempalte_messages
  belongs_to :reschedule_template_message, foreign_key: 'reschedule_template_message_id', class_name: 'TemplateMessage'
  belongs_to :cancellation_template_message, foreign_key: 'cancellation_template_message_id', class_name: 'TemplateMessage'
end

You will also need to add migration to add foreign_keys reschedule_template_message_id and cancellation_template_message_id in the clinical_systems table

Supriya Medankar0
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