我正在使用 Rails 3.2.9 并尝试将表的所有结果返回到由联接上的 department_id 过滤的categories表的任何匹配结果。incomesSQL 查询相当简单：
SELECT * FROM categories LEFT OUTER JOIN incomes ON incomes.category_id = categories.id AND dept_id = 86
现在我已经能够通过以下方式达到预期的结果joins：
Category.joins('LEFT OUTER JOIN incomes ON incomes.category_id = categories.id AND incomes.dept_id = 86')
但我不知道为什么我不能让它与include. 以下是我的模型：
类别
class Category < ActiveRecord::Base
attr_accessible :cat_code, :cat_ds
has_many :incomes, :conditions => ['dept_id = ?', 86]
end
收入
class Income < ActiveRecord::Base
attr_accessible :category_id, :year_id,:dept_id, :note
belongs_to :category
end
我尝试了许多不同的方法来获得所需的结果，但我将用上述模型说明我最近的尝试。
@cat_inc = Category.find(:all, :include => [:incomes])
但是我undefined method each for nil:NilClass在尝试debug(@cat_inc)
我很困惑为什么上面没有产生上面的 SQL 语句。有任何想法吗？
编辑
也许是一种更好的表达方式，我怎样才能有条件加入？就像上面的 SQL 语句有：AND dept_id = 86
我能得到的最接近的是：
Category.includes(:incomes).where("incomes.dept_id = ?", 86)
这给了我 LEFT OUTER JOIN 但在AND dept_id = 86加入后执行条件。
SELECT "categories"."id" AS t0_r0, "categories"."cat_code" AS t0_r1, "categories"."cat_ds" AS t0_r2, "incomes"."id" AS t1_r0, "incomes"."category_id" AS t1_r1, "incomes"."year_id" AS t1_r2, "incomes"."chart_id" AS t1_r3, "incomes"."dept_id" AS t1_r4, "incomes"."note" AS t1_r5, "incomes"."jan" AS t1_r6, "incomes"."feb" AS t1_r7, "incomes"."created_at" AS t1_r8, "incomes"."updated_at" AS t1_r9 FROM "categories" LEFT OUTER JOIN "incomes" ON "incomes"."category_id" = "categories"."id" WHERE (incomes.dept_id = 86)