Rails has_many通過查詢取決於通過表屬性

Question

has_many通過查詢有一些問題。

使用這裏的例子：http://guides.rubyonrails.org/association_basics.html#the-has_many-through-association

class Physician < ActiveRecord::Base 
    has_many :appointments 
    has_many :patients, :through => :appointments 
end 

class Appointment < ActiveRecord::Base 
    belongs_to :physician 
    belongs_to :patient 
end 

class Patient < ActiveRecord::Base 
    has_many :appointments 
    has_many :physicians, :through => :appointments 
end 

的預約表有一欄名爲appointment_date

我怎麼會得到所有的患者從具有在給定日期的預約特定醫師？

Answer 1

Patient.includes(:physicians, :appointments).where('physicians.id = ? AND appointments.appointment_date = ?', <id or ids array>, Date.today) 

其中Date.today可以隨時更改，而pysician由id或id數組指定。

你也可以這樣做：

physician = Physician.find(id) 
patients = physician.patients.includes(:appointments).where('appointments.appointment_date = ?', some_date) 

編輯：

在Rails 4和轉發，你需要添加references(:appointments)到查詢，以便在where子句中使用的約會。