Class User has_many Referrals. Referrals have an instance variable
'point_value.' So on my users/index action I want to list the user
info, total referrals, and then total points. However, I am getting the
notorious N+1 problem when running this action.
USERS CONTROLLER
def index
@users = User.find(:all, :include => :referrals)
end
INDEX VIEW
<% for user in @users %>
<tr>
<td><%= h user.email %></td>
<td>Referrals: <%= user.referrals.size %></td>
<td>Points: <%= user.total_points %>
USER.RB MODEL
has_many :referrals,
:foreign_key => "referer_id"
def total_points
self.referrals.sum :point_value
end
The index action nails me with a nasty N+2 queries (i have six user
records in the test db):
Processing UsersController#index (for 127.0.0.1 at 2009-01-02 15:49:16)
[GET]
User Load (4.3ms) SELECT * FROM "users"
Referral Load (1.4ms) SELECT "referrals".* FROM "referrals" WHERE
("referrals".referer_id IN (1,2,3,4,6,7))
Rendering template within layouts/users
Rendering users/index
SQL (0.3ms) SELECT sum("referrals".point_value) AS sum_point_value
FROM "referrals" WHERE ("referrals".referer_id = 1)
SQL (0.3ms) SELECT sum("referrals".point_value) AS sum_point_value
FROM "referrals" WHERE ("referrals".referer_id = 2)
SQL (0.3ms) SELECT sum("referrals".point_value) AS sum_point_value
FROM "referrals" WHERE ("referrals".referer_id = 3)
SQL (0.2ms) SELECT sum("referrals".point_value) AS sum_point_value
FROM "referrals" WHERE ("referrals".referer_id = 4)
SQL (0.3ms) SELECT sum("referrals".point_value) AS sum_point_value
FROM "referrals" WHERE ("referrals".referer_id = 6)
SQL (0.3ms) SELECT sum("referrals".point_value) AS sum_point_value
FROM "referrals" WHERE ("referrals".referer_id = 7)
Is this a failing of the rails .sum method to look inside the collection
or am I doing something wrong?
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