我有一个相当复杂的应用程序（超过30个表），有一些持续的N + 1问题，而且我认为这是因为我没有做一些事情＆＃39; The Rails Way™＆＃39;
我将给出一个更复杂的例子。这一个包括四个表：clins, positions_tasks, tasks和labor_hours。
positions_tasks是clins, positions（此示例不需要）和tasks以及{{1}之间的三向多对多联接}}。 labor_hours表有一年中每个月的整数字段和一些其他数据。方法has_many :labor_hours将所有月份总计为一年中的总小时数。在临床视图中，它显示临床信息和所有相关任务的表格[与其他相关数据]，并汇总每个任务的小时数total_hours。我急切地加载所有相关的表，包括labor_hours，除了labor_hours之外，所有N + 1问题都消失了。
代码片段如下。
clins_controller的急切负载：
has_many :labor_hours, :through => :positions_tasks在clins / _form.html.erb中显示表格行：
@clin = Clin.includes(:proposal).includes(:positions_tasks).includes(:tasks).includes(:labor_hours).includes(:wbss).find(params[:id])`
_task_row partial：
<tbody>
<% @clin.tasks.distinct.each do |t| %>
<%= f.fields_for :task, t do |builder| %>
<%= render "tasks/task_row", f: builder %>
<% end %>
<% end %>
</tbody>
临床模型：
<tr>
<td><%= f.object.wbs_line_item.wbs.wbs_title %></td>
<td><%= f.object.wbs_line_item.wbs_line_item %></td>
<td><%= f.object.description %></td>
<td><%= f.object.labor_hours.distinct.each.sum(&:total_hours) %>
<td><div id="jump">
<%= link_to "Edit", {:controller => :tasks, :action => :edit, :id => f.object.id } %>
</div></td>
</tr>
劳动时间模型：
class Clin < ActiveRecord::Base
nilify_blanks
belongs_to :proposal
belongs_to :parent, :class_name => "Clin"
has_many :children, :class_name => "Clin"
has_many :positions_tasks
has_many :labor_hours, :through => :positions_tasks
has_many :tasks, :through => :positions_tasks
has_many :wbs_line_items, :through => :tasks
has_many :wbss, :through => :wbs_line_items
has_many :pws_line_items, :through => :wbs_line_items
has_many :pwss, :through => :wbss
end
positionsTask模型：
class LaborHours < ActiveRecord::Base
nilify_blanks
belongs_to :positions_task
belongs_to :year
has_one :proposal, :through => :positions_task
has_many :valid_years, :through => :proposal, :source => :years
def total_hours
m1 + m2 + m3 + m4 + m5 + m6 + m7 + m8 + m9 + m10 + m11 + m12
end
end
任务模型：
class PositionsTask < ActiveRecord::Base
nilify_blanks
belongs_to :task
belongs_to :position
belongs_to :clin
has_many :labor_hours
has_one :company, :through => :position
has_one :proposal, :through => :clin
has_one :wbs_line_item, :through => :task
delegate :wbs, :to => :wbs_line_item
delegate :pws_line_items, :to => :wbs_line_item
delegate :pwss, :to => :wbs_line_item
validates_presence_of :task
validates_presence_of :position
validates_presence_of :clin
accepts_nested_attributes_for :labor_hours, allow_destroy: true
end
GET和SQL加载：
class Task < ActiveRecord::Base
nilify_blanks
belongs_to :wbs_line_item
belongs_to :task_category
has_many :positions_tasks
has_many :labor_hours, :through => :positions_tasks
has_many :positions, :through => :positions_tasks
has_many :clins, :through => :positions_tasks
has_many :proposals, :through => :positions_tasks
delegate :wbs, :to => :wbs_line_item
delegate :pws_line_items, :to => :wbs_line_item
delegate :pwss, :to => :wbs
accepts_nested_attributes_for :positions_tasks, allow_destroy: true
accepts_nested_attributes_for :labor_hours, allow_destroy: true
validates_associated :positions_tasks
end
我认为正在发生的事情是，_form.html.erb中的Started GET "/clins/11/edit" for 127.0.0.1 at 2015-07-20 17:48:49 -0400
Processing by ClinsController#edit as HTML
Parameters: {"id"=>"11"}
Clin Load (0.2ms) SELECT "clins".* FROM "clins" WHERE "clins"."id" = $1 LIMIT 1 [["id", 11]]
Proposal Load (0.2ms) SELECT "proposals".* FROM "proposals" WHERE "proposals"."id" IN (1)
PositionsTask Load (0.4ms) SELECT "positions_tasks".* FROM "positions_tasks" WHERE "positions_tasks"."clin_id" IN (11)
Task Load (0.6ms) SELECT "tasks".* FROM "tasks" WHERE "tasks"."id" IN (1, 2, 3, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 20, 23, 24)
LaborHours Load (1.1ms) SELECT "labor_hours".* FROM "labor_hours" WHERE "labor_hours"."positions_task_id" IN (1, 2, 3, 6, 7, 8, 9, 10, 12, 13, 14, 18, 19, 20, 21, 23, 24, 25, 26, 27, 30, 35, 36, 37)
WbsLineItem Load (0.5ms) SELECT "wbs_line_items".* FROM "wbs_line_items" WHERE "wbs_line_items"."id" IN (310, 312, 314, 316, 317, 318, 319, 413, 320, 321, 322, 324, 325, 326, 327, 328, 330, 333, 334)
Wbs Load (0.4ms) SELECT "wbss".* FROM "wbss" WHERE "wbss"."id" IN (1)
Clin Load (0.2ms) SELECT "clins".* FROM "clins"
Rendered tasks/_task_header.html.erb (0.0ms)
LaborHours Load (0.4ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 1]]
Rendered tasks/_task_row.erb (2.6ms)
LaborHours Load (0.3ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 2]]
Rendered tasks/_task_row.erb (1.7ms)
LaborHours Load (0.2ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 3]]
Rendered tasks/_task_row.erb (1.4ms)
LaborHours Load (0.2ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 5]]
Rendered tasks/_task_row.erb (1.3ms)
LaborHours Load (0.2ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 6]]
Rendered tasks/_task_row.erb (1.4ms)
LaborHours Load (0.2ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 7]]
Rendered tasks/_task_row.erb (1.5ms)
LaborHours Load (0.2ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 8]]
Rendered tasks/_task_row.erb (1.3ms)
LaborHours Load (0.2ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 9]]
Rendered tasks/_task_row.erb (1.3ms)
LaborHours Load (0.4ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 10]]
Rendered tasks/_task_row.erb (1.9ms)
LaborHours Load (0.2ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 11]]
Rendered tasks/_task_row.erb (1.5ms)
LaborHours Load (0.4ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 12]]
Rendered tasks/_task_row.erb (2.2ms)
LaborHours Load (0.5ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 14]]
Rendered tasks/_task_row.erb (2.6ms)
LaborHours Load (0.4ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 15]]
Rendered tasks/_task_row.erb (2.2ms)
LaborHours Load (0.2ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 16]]
Rendered tasks/_task_row.erb (1.5ms)
LaborHours Load (0.3ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 17]]
Rendered tasks/_task_row.erb (1.9ms)
LaborHours Load (0.3ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 18]]
Rendered tasks/_task_row.erb (1.6ms)
LaborHours Load (0.3ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 20]]
Rendered tasks/_task_row.erb (1.9ms)
LaborHours Load (0.2ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 23]]
Rendered tasks/_task_row.erb (1.6ms)
LaborHours Load (0.3ms) SELECT "labor_hours".* FROM "labor_hours" INNER JOIN "positions_tasks" ON "labor_hours"."positions_task_id" = "positions_tasks"."id" WHERE "positions_tasks"."task_id" = $1 [["task_id", 24]]
Rendered tasks/_task_row.erb (1.9ms)
Rendered clins/_form.html.erb (47.6ms)
Rendered clins/_errors.html.erb (0.0ms)
Rendered clins/edit.html.erb within layouts/application (48.6ms)
Rendered layouts/_header.html.erb (60.5ms)
Rendered layouts/_sidenav.html.erb (0.4ms)
Rendered layouts/_footer.html.erb (0.0ms)
Completed 200 OK in 140ms (Views: 106.4ms | ActiveRecord: 8.8ms)
和distinct.each中的急切加载会丢失，因为它传递的是任务对象而不是临床对象， /或者对total_hours的调用会导致调用它的每个对象的负载，但是我不确定如何确定它是什么，也不知道如何解决它们。
如何在没有N + 1加载劳动时间的情况下为表中的每项任务提供总计fields_for？
答案 0 :(得分：1)
我不确定，但我是一个理论。你有这个（我已经删除了刚刚关注我们的includes电话：
@clin = Clin.includes(:tasks).includes(:labor_hours).find(params[:id])
您在这里做的是急切加载与每个Clin相关联的任务以及与每个Clin相关联的LaborHours - 到目前为止，这很好，但在您看来，您正在这样做（或多或少） ）：
@clin.tasks.distinct.each do |task|
# inside the partial...
task.labor_hours...
end
在这里，您无法访问与每个Clin相关联的LaborHours - 这是您渴望加载的 - 您正在访问与每个Clin关联的每个任务相关联的LaborHours。要访问与每个Clin关联的LaborHours，您必须执行此操作：
@clin.labor_hours.each do |labor_hour|
# ...
end
但是既然你正在渲染任务（而不仅仅是工作时间），我不会认为这是你想要的。相反，你需要告诉Rails你想要加载二阶关联 - 即。与任务关联的LaborHours，而不是与Clins关联的LaborHours - 通过将哈希传递给includes：
@clin = Clin.includes(:tasks => :labor_hours).find(params[:id])
P.S。您可以进行一些额外的改进 - 例如，看起来您实际上并未使用LaborHours的任何属性，您实际上只是使用了total_hours的总和柱。但是，只要让数据库执行它，计算Ruby中的总和是一种浪费。但是，这超出了这个答案的范围。