Ruby on rails 如何在Rails中通过关联搜索组_

我不知道我是如何描述这个问题的，首先我想展示我的模型，它保持了如下的关系

category.rb

class Category < ApplicationRecord
  has_many :job_categories, dependent: :destroy
  has_many :jobs, through: :job_categories
end

class JobCategory < ApplicationRecord
  belongs_to :category, counter_cache: :jobs_count
  belongs_to :job
end

父级是一个列，它维护类似组的技术，在这个ruby、rails、programming等下，它与技术相关

下面是我对按类别显示组的查询

Category.select(:id, :name, :parent).group_by{|p| p.parent}

就这样表现出来的

技术

红宝石 轨道 等 现在我想按技术显示组中的所有作业，我有一个类似这样的查询

Job.joins(:categories).where('lower(categories.parent) LIKE lower(?)', "%#{params[:parent]}%")

它显示了错误的输出，比如如果我只有一个作业，分类是ruby，rails，那么这个作业显示了两次，一次是ruby，一次是rails

---

谢谢

您的关联是正确的，您可以通过以下方式检索某些类别的所有唯一作业：

Job.joins(:job_categories).joins(:categories).where('lower(categories.parent) LIKE lower(?)', "%#{params[:parent]}%").distinct

这将把作业与中间表job_类别和相关键上的作业连接起来，where子句将允许您选择要检索的内容

SELECT DISTINCT "jobs" .*
FROM "jobs" INNER
JOIN "job_categories" ON "job_categories" ."job_id" = "jobs" ."id" INNER
JOIN "job_categories" "job_categories_jobs_join" ON "job_categories_jobs_join" ."job_id" = "jobs" ."id" INNER
JOIN "categories" ON "categories" ."id" = "job_categories_jobs_join" ."category_id"
WHERE
(
 lower ( categories.parent ) LIKE lower ( "Technology" ) )

更新： 实际上，我们也不需要显式连接到job_类别，以下内容就足够了：

Job.joins(:categories).where('lower(categories.parent) LIKE lower(?)', "%#{params[:parent]}%").distinct

SELECT DISTINCT "jobs".* FROM "jobs" INNER JOIN "job_categories" ON "job_categories"."job_id" = "jobs"."id" INNER JOIN "categories" ON "categories"."id" = "job_categories"."category_id" WHERE (lower ( categories.parent ) LIKE lower ( "Technology" ))

---

只有少数几个其他选项可用于获取和分组具有关联的记录，这些选项有很多：

# Filtering by query
Job.joins(:categories).select('jobs.id, jobs.name, categories.parent').where('lower(categories.parent) LIKE lower(?)', "Technology").distinct.inspect
# => #<ActiveRecord::Relation [#<Job id: 1, name: "Developer">, #<Job id: 2, name: "Debugger">]>

# Grouping by categories.parent, return a hash
Job.joins(:categories).select('jobs.id, jobs.name, categories.parent').all.distinct.group_by(&:parent)
# => {"Technology"=>[#<Job id: 1, name: "Developer">, #<Job id: 2, name: "Debugger">], "Mechanics"=>[#<Job id: 3, name: "Technic">]}

# Accessing the hash by key
Job.joins(:categories).select('jobs.id, jobs.name, categories.parent').all.distinct.group_by(&:parent)["Technology"]
#=> [#<Job id: 1, name: "Developer">, #<Job id: 2, name: "Debugger">]

---

如果只需要按顺序列出它们，为什么要应用where条件？现在显示三重而不是双重，请查看日志中的查询SELECT COUNT*from jobs INTERNAL job job job job job job job\U CATEGORES ON job\U categories job\U job\U job job\U id=job.id INTERNAL job job job job job\U categories job\U job\U job job\U CONTIEGORES ONcategories.id=job\u categories\u jobs\u join.categories\u id其中lowercategories.parent类较低的“%Technology%”添加。在关系结尾处不同。job.join:job\u categories.joins:categories.WHERE'lowercategories.parent类较低的“，%{params[：parent]}%.distinct此查询的好处是它仍然是一个ActiveRelation，使您能够与其他查询链接，并在需要时加入。

Job.joins(:categories).where('lower(categories.parent) LIKE lower(?)', "%#{params[:parent]}%").distinct

SELECT DISTINCT "jobs".* FROM "jobs" INNER JOIN "job_categories" ON "job_categories"."job_id" = "jobs"."id" INNER JOIN "categories" ON "categories"."id" = "job_categories"."category_id" WHERE (lower ( categories.parent ) LIKE lower ( "Technology" ))

# Filtering by query
Job.joins(:categories).select('jobs.id, jobs.name, categories.parent').where('lower(categories.parent) LIKE lower(?)', "Technology").distinct.inspect
# => #<ActiveRecord::Relation [#<Job id: 1, name: "Developer">, #<Job id: 2, name: "Debugger">]>

# Grouping by categories.parent, return a hash
Job.joins(:categories).select('jobs.id, jobs.name, categories.parent').all.distinct.group_by(&:parent)
# => {"Technology"=>[#<Job id: 1, name: "Developer">, #<Job id: 2, name: "Debugger">], "Mechanics"=>[#<Job id: 3, name: "Technic">]}

# Accessing the hash by key
Job.joins(:categories).select('jobs.id, jobs.name, categories.parent').all.distinct.group_by(&:parent)["Technology"]
#=> [#<Job id: 1, name: "Developer">, #<Job id: 2, name: "Debugger">]