如何通过 has_many 关联创建一个 has_one？

Question

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. eg:

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.

Answer 1

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

Answer 2

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