Rails与has_many通过关系嵌套连接

我有一个DB存储学生对测验问题的答案。这些与学生学习成果相关，我想通过下面描述的一系列关系进行审查。我试图计算正确回答了多少个问题，并为每个学生的学习成果错误地回答了多少个问题，但我仍然收到错误。预先感谢您提供的任何帮助。Rails与has_many通过关系嵌套连接

一般的映射是

“答案”回答了这个测试，涵盖许多“KnowledgeTopic”问题（“KtCoveredBySLO”）“StudentLearningOutcome”

我车型有以下关系：

class Answer < ActiveRecord::Base 
    belongs_to :KnowledgeTopic 
end 

class KnowledgeTopic < ActiveRecord::Base 
    has_many :answers 
    has_many :kt_covered_by_slos 
    has_many :student_learning_outcomes, through: :kt_covered_by_slos 
end 

class KtCoveredBySlo < ActiveRecord::Base 
    belongs_to :StudentLearningOutcome 
    belongs_to :KnowledgeTopic 
end 

class StudentLearningOutcome < ActiveRecord::Base 
    has_many :kt_covered_by_slos 
    has_many :knowledge_topics, through: :kt_covered_by_slos 
end

我尝试运行的查询是：

@answers = Answer.joins(:KnowledgeTopic => {:kt_covered_by_slos => :StudentLearningOutcome}) 

.select('student_learning_outcomes.id As student_learning_outcomes_id', 
       :is_correct, "count(answers.id) AS total_answers") 

.group('student_learning_outcomes.id', :is_correct)

我收到的错误是：

的SQLite3 ::的SQLException：没有这样的列： kt_covered_by_slos.knowledge_topic_id：SELECT student_learning_outcomes.id作为student_learning_outcomes_id， “答案” “is_correct”，计数（ answers.id）AS total_answers从 “answers”INNER JOIN“knowledge_topics”ON“knowledge_topics”。“id” =“answers”。“KnowledgeTopic_id”INNER JOIN“kt_covered_by_slos”ON“kt_covered_by_slos”。“knowledge_topic_id”=“knowledge_topics” 。“id”
INNER JOIN“student_learning_outcomes”ON。“student_learning_outcomes”， “ID”= “kt_covered_by_slos” “StudentLearningOutcome_id” GROUP BY student_learning_outcomes.id，is_correct

迁移：

class CreateKtCoveredBySlos < ActiveRecord::Migration 
    def change 
    create_table :kt_covered_by_slos do |t| 
     t.references :StudentLearningOutcome, index: true 
     t.references :KnowledgeTopic, index: true 

     t.timestamps 
    end 
    end 
end 

class CreateAnswers < ActiveRecord::Migration 
    def change 
    create_table :answers do |t| 
     t.references :Question, index: true 
     t.references :Section, index: true 
     t.references :Student, index: true 
     t.references :KnowledgeTopic, index: true 
     t.boolean :is_correct 
     t.string :answer_text 
     t.references :Enroll, index: true 

     t.timestamps 
    end 
    end 
end 

class CreateKnowledgeTopics < ActiveRecord::Migration 
    def change 
    create_table :knowledge_topics do |t| 
     t.string :knowledge_area 
     t.string :knowledge_unit 
     t.string :knowledge_topic 
     t.integer :year_added 
     t.boolean :active 
     t.integer :correct_answers 
     t.integer :incorrect_answers 
     t.integer :temp_correct_answer 
     t.integer :temp_incorrect_answer 
     t.timestamps 
    end 
    end 
end 

class CreateStudentLearningOutcomes < ActiveRecord::Migration 
    def change 
    create_table :student_learning_outcomes do |t| 
     t.string :accredidation_body 
     t.string :title 
     t.string :description 
     t.integer :year_added 
     t.boolean :active 
     t.integer :correct_answers 
     t.integer :incorrect_answers 
     t.integer :temp_correct_answer 
     t.integer :temp_incorrect_answer 
     t.timestamps 
    end 
    end 
end

来源

2014-11-25 Katie T

运行查询您可以使用'Answer'，'KtCoveredBySlo'进行迁移来更新您的问题吗？您的查询为'KnowledgeTopic'的外键显示两个不同的列名。 – vee 2014-11-25 14:29:56

你还可以请你以更容易阅读的方式来构建你的查询，比如把它分成几行。 – 2014-11-25 14:32:15

您是否试图遵循rails惯例，并在模型中的迁移和关联声明中使用snake_case命名，或者它不是一个选项？ – ave 2014-11-25 15:00:40

谢谢大家。使用Ave的解释，我更改了参考名称，然后相应地更新了其他所有内容。之后，我可以用

@answers = Answer.joins(knowledge_topic: :student_learning_outcomes) 
.select('student_learning_outcomes.id As student_learning_outcomes_id', :is_correct, 
    "count(answers.id) AS total_answers") 
.group('student_learning_outcomes.id', :is_correct)

来源

2014-12-02 14:31:03

Rails与has_many通过关系嵌套连接

回答

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