Rails左外连接

Question

Let's say i have the following models:

class Employee < ActiveRecord::Base
    has_many :shifts    
end

class Shift < ActiveRecord::Base
    belongs_to :employee
end

In my controller I want to load all employees including their shifts in a certain date range. But I also want to include employees without any shifts in that range.

In my controller I tried:

@employees.joins("LEFT OUTER JOIN shifts ON employees.id = shifts.employee_id").where('shifts.starts_at BETWEEN ? and ?', weekBegin, weekEnd).to_json(:include => :shifts)

But this still just returns the employees with shifts in that date range. I also want to return employees with no shifts in that date range.

How does such a query work?

Answer 1

You should include conditions on the shifts start time into the join statement:

@employees.joins("
     LEFT OUTER JOIN shifts 
     ON employees.id = shifts.employee_id
     AND shifts.starts_at 
         BETWEEN #{ActiveRecord::Base.sanitize(weekBegin)} 
             AND #{ActiveRecord::Base.sanitize(weekEnd)}
").to_json(:include => :shifts)

Answer 2

您可以尝试这样做

LEFT OUTER JOIN shifts ON employees.id = shifts.employee_id AND shifts.starts_at BETWEEN weekBegin and weekEnd