ruby-on-rails - 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类(class)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 has many:

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

这是 RoR 文档中对此选项的描述:

If true, duplicates will be omitted from the collection. Useful in conjunction with :through.

此外，为了避免重复项首先进入数据库，您可以使用唯一的数据库索引，它可能看起来像这样:

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