Rails 3.如何从查询结果中删除重复的关联记录？

Question

我有@invoices,其中包含与特定预定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,一些发票可能会重复.例如,@invoices - @scheduled_course.invoices可能输出...

=> [#<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？

Answer 1

您可以将:uniq选项传递给多个:

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

以下是此选项的RoR文档的说明:

如果为true,则将从集合中省略重复项.与以下内容结合使用:通过.

此外,为避免重复进入数据库,您可以使用唯一的DB索引,可能如下所示:

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