rails select and include

Question

Can anyone explain this?

Project.includes([:user, :company])

This executes 3 queries, one to fetch projects, one to fetch users for those proje

Answer 1

Rails has always ignored the select argument(s) when using include or includes. If you want to use your select argument then use joins instead.

You might be having a problem with the query gem you're talking about but you can also include sql fragments using the joins method.

Project.select("name").joins(['some sql fragement for users', 'left join companies c on c.id = projects.company_id'])

I don't know your schema so i'd have to guess at the exact relationships but this should get you started.

Answer 2

I had the same problem with select and includes. For eager loading of associated models I used native Rails scope 'preload' http://apidock.com/rails/ActiveRecord/QueryMethods/preload It provides eager load without skipping of 'select' at scopes chain.

I found it here https://github.com/rails/rails/pull/2303#issuecomment-3889821

Hope this tip will be helpful for someone as it was helpful for me.

Answer 3

Allright so here's what I came up with...

.joins("LEFT JOIN companies companies2 ON companies2.id = projects.company_id LEFT JOIN project_types project_types2 ON project_types2.id = projects.project_type_id LEFT JOIN users users2 ON users2.id = projects.user_id") \
.select("six, fields, I, want")

Works, pain in the butt but it gets me just the data I need in one query. The only lousy part is I have to give everything a model2 alias since we're using meta_search, which seems to not be able to figure out that a table is already joined when you specify your own join conditions.

Answer 4

I wanted that functionality myself,so please use it. Include this method in your class

#ACCEPTS args in string format "ASSOCIATION_NAME:COLUMN_NAME-COLUMN_NAME"

def self.includes_with_select(*m)
    association_arr = []
    m.each do |part|
      parts = part.split(':')
      association = parts[0].to_sym
      select_columns = parts[1].split('-')
      association_macro = (self.reflect_on_association(association).macro)
      association_arr << association.to_sym
      class_name = self.reflect_on_association(association).class_name 
      self.send(association_macro, association, -> {select *select_columns}, class_name: "#{class_name.to_sym}")
    end
    self.includes(*association_arr)
  end

And you will be able to call like: Contract.includes_with_select('user:id-name-status', 'confirmation:confirmed-id'), and it will select those specified columns.

Answer 5

I might be totally missing something here but select and include are not a part of ActiveRecord. The usual way to do what you're trying to do is like this:

Project.find(:all, :select => "users.name", :include => [:user, :company], :joins => "LEFT JOIN users on projects.user_id = users.id")

Take a look at the api documentation for more examples. Occasionally I've had to go manual and use find_by_sql:

Project.find_by_sql("select users.name from projects left join users on projects.user_id = users.id")

Hopefully this will point you in the right direction.