Rails 4 - how to give alias names to includes() and joins() in active record querying

Question

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

Answer 1

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.