如何访问对虾表格单元格中内容的另一个模型/记录？

Question

我正在构建一个带有表格(对虾和对虾-表格)的PDF，其中特定章节的所有教育目标(EO)都与其用例(UC)一起显示。我直接得到了EO，但不知道如何让UC进入单元格。这是我的代码。也许有人比我更有想法，或者知道如何做得更好。提前感谢！

class UseCase < ApplicationRecord
    has_and_belongs_to_many :educational_objectives
end

class EducationalObjective < ApplicationRecord
    has_and_belongs_to_many :use_cases
end

app/pdfs/章节_pdf.rb

require 'prawn'

class ChapterPdf < Prawn::Document
    def initialize(eo, chapter)
        @educational_objectives = eo
        @chapter = chapter
        @subject_id = @chapter.subject_id

        chapter_header
        chapter_text
        items
    end

    ...

    def items
        table_data = []

        @educational_objectives.map do |item|
            table_data << [item.position, item.educational_objective, use_cases(item.id)]
        end
        ...
    end

    def use_cases(id)
      ucs = @educational_objectives.joins(:use_cases).
                                where(educational_objectives: {id: id}).
                                select(:use_case)
      ucs.join do |uc|
        uc
      end
    end
end

当我查看服务器日志时，我看到以下内容：

SELECT "use_case" FROM "educational_objectives" INNER JOIN "educational_objectives_use_cases" ON "educational_objectives_use_cases"."educational_objective_id" = "educational_objectives"."id" INNER JOIN "use_cases" ON "use_cases"."id" = "educational_objectives_use_cases"."use_case_id" WHERE "educational_objectives"."chapter_id" = ? AND "educational_objectives"."id" = ?  [["chapter_id", 9], ["id", 169]]

SELECT  1 AS one FROM "educational_objectives" INNER JOIN "educational_objectives_use_cases" ON "educational_objectives_use_cases"."educational_objective_id" = "educational_objectives"."id" INNER JOIN "use_cases" ON "use_cases"."id" = "educational_objectives_use_cases"."use_case_id" WHERE "educational_objectives"."chapter_id" = ? AND "educational_objectives"."id" = ? LIMIT ?  [["chapter_id", 9], ["id", 171], ["LIMIT", 1]]

在我的PDF中，我看到了单元格

#<EducationalObjective:0x00007f8569997370>#<EducationalObjecti
ve:0x00007f85699971e0>#<EducationalObjective:0x00007f85699970
50>

我的错误在哪里？然后我想用逗号分隔显示它...是的，我是一个新手，非常感谢你的帮助！

Answer 1

has_and_belongs_to_many关联提供了a number of helper methods -对于您的情况，您将能够调用educational_objective.use_cases来返回相关记录的集合。

这意味着您可以删除use_cases方法，并使用类似于以下内容的内容：

  table_data = @educational_objectives.map do |item|
    [item.position, item.educational_objective, item.use_cases]
  end

由于您使用的是map，因此不需要使用在此之外定义的数组。

这假设上例中的item是EducationalObjective的一个实例，尽管我对此有点困惑，因为您也在调用item.educational_objective。

如果这对你有什么帮助或者你有任何问题，请告诉我。