Ruby on rails 轨道3。如何从查询结果中删除重复的关联记录？

我有@invoices，其中包含与特定计划课程相关的所有发票

scheduled_course has_many :invoices, through => :enrollments
invoices belongs_to :scheduled_courses

@scheduled_course = ScheduledCourse.find(params[:id])
@invoices = @scheduled_course.invoices

现在，有些发票可能是重复的。例如，

@invoices-@scheduled_course.invoices

可能会输出

=> [#<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2bcc9c,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">, 
#<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2b828c,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">, 
#<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2b7e54,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">, 
#<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2b7a1c,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">, 
#<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2b75e4,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">, #<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2b7198,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">

=>，
#, 
#, 
#, 
#, #

如何从结果中删除重复的对象

@scheduled_course.invoices.uniq(&:id) # uniq elements in the array by their id

---

只需使用

@scheduled\u course.invoices.uniq

也应该可以使用。

您可以将

：uniq

选项传递到以下位置：

has_many :invoices, :through => :enrollments, :uniq => true

以下是RoR文档对此选项的描述：

如果为true，则将从集合中忽略重复项。与：至结合使用非常有用

此外，为了避免重复数据首先进入数据库，您可以使用唯一的数据库索引，该索引可能如下所示：

add_index :enrollments, [:invoice_id, :scheduled_course_id], :unique => true

---

您不能直接调用uniq吗？使用uniq会将查询转换为数组，这可能会对性能产生负面影响。请记住#uniq会将ActiveRecord关联转换为发票数组，这可能会对性能和获取元素所需的时间产生负面影响。是的，请改用

distinct

。Thi的解决方案在Rails 4.0中将不受欢迎，甚至可能在Rails 4.1中不存在，因此建议使用替代的lambda版本：has_many:invoices、>{get unique elements}、：through=>：enrollments