Question

此github gist中提供了一个自运行模板，其中包含所有要自行测试的模型 - 运行它并触发错误。

为了使其可视化，结构如下所示：

Colors
  |n|
  |:|
  |1| -----
Houses n:n Conditions
  |n| -----
  |:|
  |1|
People

从空白数据库开始，我创建了一些测试数据（控制台命令，省略了返回值以保持清晰）：

irb(main):001:0> Condition.create(condition: :damaged)
irb(main):002:0> house = House.create(conditions: [Condition.first])
irb(main):003:0> person = Person.create
irb(main):004:0> house.person = person
irb(main):005:0> house.save

所以现在我有一些测试数据。让我们检索一下这个人的房子（根据定义，这只是受损房屋）：

irb(main):006:0> person.damaged_houses
  House Load (0.2ms)
  SELECT "houses".* FROM "houses" 
    INNER JOIN "conditions_houses" ON "conditions_houses"."house_id" = "houses"."id"
    INNER JOIN "conditions" ON "conditions"."id" = "conditions_houses"."condition_id"
    WHERE "houses"."person_id" = ? AND "conditions"."condition" = 'damaged'
    [["person_id", 1]]
=> #<ActiveRecord::Associations::CollectionProxy [#<House id: 1, person_id: 1>]>

一切顺利，返回损坏的房子并且sql正确地加入了conditions表。现在我想得到人的所有颜色，这被定义为房屋的所有颜色，房屋仍然只是受损的房屋。这应该返回一个空集合（因为数据库中还没有颜色）。

irb(main):007:0> person.damaged_colors
  Color Load (0.4ms) 
  SELECT "colors".* FROM "colors"
    INNER JOIN "houses" ON "colors"."house_id" = "houses"."id" 
    WHERE "houses"."person_id" = ? AND "conditions"."condition" = 'damaged'
    [["person_id", 1]]
SQLite3::SQLException: no such column: conditions.condition:
  SELECT "colors".* FROM "colors"
    INNER JOIN "houses" ON "colors"."house_id" = "houses"."id"
    WHERE "houses"."person_id" = ? AND "conditions"."condition" = 'damaged'

从sql字符串中可以清楚地看到连接表conditions缺失，因此conditions.condition不可用。如果我看到它正确，只需要查询之前的字符串：

INNER JOIN "conditions_houses" ON "conditions_houses"."house_id" = "houses"."id"
INNER JOIN "conditions" ON "conditions"."id" = "conditions_houses"."condition_id"

所以查询应该是：

SELECT "colors".* FROM "colors"
  INNER JOIN "houses" ON "colors"."house_id" = "houses"."id"
  INNER JOIN "conditions_houses" ON "conditions_houses"."house_id" = "houses"."id"
  INNER JOIN "conditions" ON "conditions"."id" = "conditions_houses"."condition_id"
  WHERE "houses"."person_id" = ? AND "conditions"."condition" = 'damaged'

这是一个rails bug还是我做错了？为什么缺少联接conditions？

代码：

class Color < ActiveRecord::Base
    belongs_to :house
end

class Condition < ActiveRecord::Base
    has_and_belongs_to_many :houses
end

class House < ActiveRecord::Base
    has_many :colors
    belongs_to :person

    has_and_belongs_to_many :conditions

    scope :damaged, -> { joins(:conditions).where(:'conditions.condition' => 'damaged') }
end

class Person < ActiveRecord::Base
    has_many :damaged_houses, -> { damaged }, :class_name => "House"
    has_many :damaged_colors, through: :damaged_houses, :source => :colors
end

Answer 1

所以我能够通过修改以下内容来让你的要点得以运行：

has_many :damaged_colors, through: :damaged_houses, :source => :colors

到

has_many :damaged_colors, -> { joins({house: :conditions}).where(:'conditions.condition' => 'damaged') }, through: :damaged_houses, :source => :colors

在评论中提到的HABTM关联似乎是一个ActiveRecord错误...希望这有助于平均时间......

有趣的是，我把你的要点改为hm：hm并且有同样的问题......

rails嵌套has_many与外部作用域连接未命中连接表：sql错误

1 个答案: