rails select and include

Can anyone explain this?

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

This executes 3 queries, 开发者_开发技巧one to fetch projects, one to fetch users for those projects and one to fetch companies.

Project.select("name").includes([:user, :company])

This executes 3 queries, and completely ignores the select bit.

Project.select("user.name").includes([:user, :company])

This executes 1 query with proper left joins. And still completely ignores the select.

It would seem to me that rails ignores select with includes. Ok fine, but why when I put a related model in select does it switch from issuing 3 queries to issuing 1 query?

Note that the 1 query is what I want, I just can't imagine this is the right way to get it nor why it works, but I'm not sure how else to get the results in one query (.joins seems to only use INNER JOIN which I do not in fact want, and when I manually specifcy the join conditions to .joins the search gem we're using freaks out as it tries to re-add joins with the same name).

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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.

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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.

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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.

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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.

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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.

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The preload solution doesn't seem to do the same JOINs as eager_load and includes, so to get the best of all worlds I also wrote my own, and released it as a part of a data-related gem I maintain, The Brick.

By overriding ActiveRecord::Associations::JoinDependency.apply_column_aliases() like this then when you add a .select(...) then it can act as a filter to choose which column aliases get built out.

With gem 'brick' loaded, in order to enable this selective behaviour, add the special column name :_brick_eager_load as the first entry in your .select(...), which turns on the filtering of columns while the aliases are being built out. Here's an example:

Employee.includes(orders: :order_details)
        .references(orders: :order_details)
        .select(:_brick_eager_load,
                'employees.first_name', 'orders.order_date', 'order_details.product_id')

Because foreign keys are essential to have everything be properly associated, they are automatically added, so you do not need to include them in your select list.

Hope it can save you both query time and some RAM!