"where" doesn't work when on_shard (Rails 3.2)

[lukkry]

ActiveRecordShards tries to read from not sharded database when calling

ActiveRecord::Base.on_shard(1){ Project.where(:id => 1) }

Steps to reproduce:

• create a new rails 3.2.14 app
• add active_record_shards to Gemfile
• create database.yml

development:
  adapter: mysql2
  encoding: utf8
  database: mango
  pool: 5
  host: 127.0.0.1
  username: root
  password:
  slave:
    database: mango_slave
  shards:
    1:
      database: mango_shard0
      slave:
        database: mango_shard0_slave
    2:
      database: mango_shard1
      slave:
        database: mango_shard1_slave

• $ bundle exec rails g model Project name:string

class CreateProjects < ActiveRecord::Migration
  shard :all

  def change
    create_table :projects do |t|
      t.string :name

      t.timestamps
    end
  end
end

• $ bundle exec rake db:migrate
• $ bundle exec rails c

1.9.3-p429 :008 > ActiveRecord::Base.on_shard(1){ Project.connection.current_database }
   (2.5ms)  SELECT DATABASE() as db
 => "mango_shard0"
1.9.3-p429 :006 > ActiveRecord::Base.on_shard(1){ Project.all }
  Project Load (0.3ms)  SELECT `projects`.* FROM `projects`
 => []
1.9.3-p429 :001 > ActiveRecord::Base.on_shard(1){ Project.where(:id => 1) }
  Project Load (0.3ms)  SELECT `projects`.* FROM `projects` WHERE `projects`.`id` = 1
ActiveRecord::StatementInvalid: Mysql2::Error: Table 'mango.projects' doesn't exist: SELECT `projects`.* FROM `projects`  WHERE `projects`.`id` = 1

Am I missing something obvious here?

[lukkry]

It works if I set default_shard earlier

$ be rails c
Loading development environment (Rails 3.2.14)
1.9.3-p429 :001 > ActiveRecord::Base.default_shard = 1
 => 1
1.9.3-p429 :002 > ActiveRecord::Base.on_shard(1){ Project.where(:id => 1) }
  Project Load (0.3ms)  SELECT `projects`.* FROM `projects` WHERE `projects`.`id` = 1
 => []

[osheroff]

What's probably happening here is that the call to 'where' is returning an active relation object, ie a "promise" that is then evaluated outside the block (probably when irb calls "to_s") on it. Unfortunately, at that point we've already switched off the shard again.

On Sep 2, 2013, at 1:13 PM, Lukasz Krystkowiak [email protected] wrote:

ActiveRecordShards tries to read from not sharded database when calling

ActiveRecord::Base.on_shard(1){ Project.where(:id => 1) }
Steps to reproduce:

create a new rails 3.2.14 app
add active_record_shards to Gemfile
create database.yml
development:
adapter: mysql2
encoding: utf8
database: mango
pool: 5
host: 127.0.0.1
username: root
password:
slave:
database: mango_slave
shards:
1:
database: mango_shard0
slave:
database: mango_shard0_slave
2:
database: mango_shard1
slave:
database: mango_shard1_slave
$ bundle exec rails g model Project name:string
class CreateProjects < ActiveRecord::Migration
shard :all

def change
create_table :projects do |t|
t.string :name

  t.timestamps
end

end
end
$ bundle exec rake db:migrate
$ bundle exec rails c
1.9.3-p429 :008 > ActiveRecord::Base.on_shard(1){ Project.connection.current_database }
(2.5ms) SELECT DATABASE() as db
=> "mango_shard0"
1.9.3-p429 :006 > ActiveRecord::Base.on_shard(1){ Project.all }
Project Load (0.3ms) SELECT projects.* FROM projects
=> []
1.9.3-p429 :001 > ActiveRecord::Base.on_shard(1){ Project.where(:id => 1) }
Project Load (0.3ms) SELECT projects.* FROM projects WHERE projects.id = 1
ActiveRecord::StatementInvalid: Mysql2::Error: Table 'mango.projects' doesn't exist: SELECT projects.* FROM projects WHERE projects.id = 1
Am I missing something obvious here?

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[lukkry]

You're right, it works as expected when it's evaluated inside the block

1.9.3-p429 :001 > ActiveRecord::Base.on_shard(1){ Project.where(:id => 1).first }
  Project Load (0.3ms)  SELECT `projects`.* FROM `projects` WHERE `projects`.`id` = 1 LIMIT 1
 => nil

[osheroff]

re-opening, since this is very violiating of principle of least surprises -- any ideas on what it would take to stash the shard-selection alongside the activerelation promise object and switch in and out of the shard for the duration of the query?

[staugaard]

Something like what I did for the old ticket archive. RelationFromArchive in https://github.com/zendesk/zendesk/blob/master/lib/archive.rb