Rails 4-如何在活动记录查询中为include（）和joins（）赋予别名 [英] Rails 4 - how to give alias names to includes() and joins() in active record querying

问题描述

我如何给例如一个别名 includes（）？
给出以下内容：

• 用户：活动记录模型


• 学生：活动记录模型，从用户（STI）继承


• 教师：活动记录模型


• 项目：活动记录模型

以下是一些示例：

首例（更多的STI协会）

  Project.all.includes（：students，：teachers）.order（'teachers_projects.name ASC'）＃教师订单
 Project.all.includes（：students，：teachers）.order（'users.name ASC'）＃学生订单
  

Rails在SQL中为：teachers 自动使用别名 teachers_projects 。如何覆盖此内容，以便可以在SQL中使用别名 teachers 代替 teachers_projects ？ ：学生获得别名用户。

此示例失败：

  Project.all.includes（：students，：teachers）.order（'teachers .name ASC'）
 Project.all.includes（：students，：teachers）.order（'students.name ASC'）
 Project.all.includes（：students，：teachers）.order（ 'students_projects.name ASC'）
  

第二种情况（一个STI协会）

如果我仅使用：学生（不使用：教师）在方法 includes（）中，Rails使用STI基类名称 users 的名称别名（不包含<$ c附加了$ c> _projects ）用于：学生：

  Project.all.includes（：students）.order（'users.name ASC'）＃对学生的订购
  

此示例失败：

  Project.all.includes（：students） .order（'students.name ASC'）
 Project.all.inclu des（：students）.order（'students_projects.name ASC'）
  

问题

可能存在以下内容：

  Project.all。 include（：students）.alias（students：：my_alias）
  

铁路别名跟踪器

https://github.com/rails/rails/blob/v4.2.0/activerecord/lib/active_record/associations/alias_tracker.rb#L59

测试应用

https://gist.github.com/phlegx/add77d24ebc57f211e8b

https://github.com/phlegx/rails_query_alias_names

解决方案

Arel实际上确实有一个lias方法。

  student_alias = Student.arel_table.alias（：my_student_table_alias）
  

：这将需要您使用更多手工制作的Arel并手动进行连接。如果您不习惯Arel中的联接，可能会变得有些复杂。

  student_alias_join = student_alias.create_on（
 Project.arel_table [：primary_key] .eq（student_alias [：project_id]）
）
 
 Project.joins（
 Project.arel_table.create_join（
 student_alias，student_alias_join，Arel :: Nodes :: OuterJoin 
）
）.order（...）
  

应该执行类似的操作。
当然，使用：my_student_table_alias 作为参数将其放入某些Class方法中会使其更加整洁和可重用，因为在控制器中看起来有些混乱。 p>

How can I give an alias name for e.g. includes()? Following is given:

• User: active record model
• Student: active record model, inherits from User (STI)
• Teacher: active record model, inherits from User (STI)
• Project: active record model

Here some examples:

FIRST CASE (more STI associations)

Project.all.includes(:students, :teachers).order('teachers_projects.name ASC') # order on teachers
Project.all.includes(:students, :teachers).order('users.name ASC') # order on students

Rails uses automatically alias name teachers_projects for :teachers in the SQL. How can I overwrite this, so that I can use alias name teachers instead of teachers_projects in the SQL? :students gets alias name users.

This examples fails:

Project.all.includes(:students, :teachers).order('teachers.name ASC')
Project.all.includes(:students, :teachers).order('students.name ASC')
Project.all.includes(:students, :teachers).order('students_projects.name ASC')

SECOND CASE (one STI association)

If I use only :students (without :teachers) in method includes(), Rails uses name alias of the STI base class name users (without _projects attached) for :students:

Project.all.includes(:students).order('users.name ASC') # order on students

This examples fails:

Project.all.includes(:students).order('students.name ASC')
Project.all.includes(:students).order('students_projects.name ASC')

QUESTION

Might exist something like:

Project.all.includes(:students).alias(students: :my_alias)

RAILS ALIAS TRACKER

https://github.com/rails/rails/blob/v4.2.0/activerecord/lib/active_record/associations/alias_tracker.rb#L59

TESTING APP

https://gist.github.com/phlegx/add77d24ebc57f211e8b

https://github.com/phlegx/rails_query_alias_names

解决方案

Arel does actually have an alias method.

student_alias = Student.arel_table.alias(:my_student_table_alias)

caveat: this will require you to use even more handcrafted Arel and do the join manually. And the joins in Arel can get a bit complicated if you're not used to them.

student_alias_join = student_alias.create_on(
  Project.arel_table[:primary_key].eq(student_alias[:project_id])
)

Project.joins(
  Project.arel_table.create_join(
    student_alias, student_alias_join, Arel::Nodes::OuterJoin
  )
).order(...)

Something like this should do it. Of course putting this into some Class method with :my_student_table_alias as parameter would make it more tidy and reusable as this would look a bit messy in a controller.

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