将SQL查询转换为Rails Active Record查询

Question

Anyhow, I am able to fetch result in rails console by putting lines below

group = UserGroup.find_by_sql("select user_group_memberships.user_group_id, sum(-bets.amount + bets.amount_paid) as bankroll_net_profit  from bets  inner join user_group_memberships ON bets.user_id = user_group_memberships.user_id GROUP BY user_group_memberships.user_group_id")

It gives result below:

-+-----------------------------------+
| user_group_id | bankroll_net_profit |
+---------------+---------------------+
|             1 |                4765 |
|            57 |                1517 |
|            58 |                 -20 |
|            62 |                1517 |
|            64 |                1517 |
|            66 |                1507 |
|            67 |                 995 |
|            82 |                1517 |
-+-----------------------------------+

But I needed to get active records in groups variable but I got an Array (checked via group.class ) so I won't be able to do extra calculations in active records.

Can anybuddy help me to find Active Record of Above Mysql Query: I need Model.joins(:another_model)

Associations are below:

 class UserGroup < ActiveRecord::Base
   has_many :user_group_memberships
   has_many :users, :through => :user_group_memberships

class User < ActiveRecord::Base
  has_many :user_group_memberships
  has_many :user_groups, :through => :user_group_memberships


class Bet < ActiveRecord::Base
  belongs_to :user

Answer 1

It's probably not exact, but I imagine you'd want something like this:

UserGroup.
  select('user_groups.*, sum(-bets.amount + bets.amount_paid) as bankroll_net_profit').
  joins(:users => :bets).
  group('user_groups.id')

Hopefully that will at least be enough to point you in the right direction. Given the associations you show, Rails should be smart enough to join UserGroups to UserGroupMemberships , UserGroupMemberships to Users , and Users to Bets .

When you use .select , you can fetch the non-attribute values from the resulting ActiveRecord objects, so if you save this relation as user_groups , you should be able to call user_groups.first.bankroll_net_profit . Note that if you're using PostGreSQL, this will be a String , and need to be converted to the correct data type with .to_f or whatever.