Question

我的Rails 2.3应用程序中有以下数据模型

class PortraitSubject
  has_many    :portraits
  has_one     :primary_portrait, :through => :portraits, :source => :asset, :conditions => ['portraits.primary = ?', true]
  has_many    :supplementary_portraits, :through => :portraits, :source => :asset, :conditions => ['portraits.primary = ?', false]

  ...
end

class Portrait
  belongs_to :portrait_subject
  belongs_to :asset

  ...
end

我想使用Rails构建关联的代理模型，但尝试构建primary_portrait失败并出现异常。即。

# This works
subject = PortraitSubject.new
subject.supplementary_portraits.build
subject.save

# This doesn't
subject = PortraitSubject.new
subject.build_primary_portrait
# => NoMethodError: undefined method `build_primary_portrait' for #<PortraitSubject:0x007ff16fe38948>

我不确定我做错了什么。通过Rails指南查看，看起来应该可以使用has_one关系。任何帮助将不胜感激。

Answer 1

你会对这些命名惯例感到疯狂。 PrimaryPortrait和SecondaryPortrait应该是Portrait的特殊情况，而不是属于Portrait的资产。它已经破坏了你的设计，你不能建立一个。

试试这个：

class PortraitSubject
  has_many    :portraits
  has_one     :primary_portrait, :conditions => {:primary => true}
  has_many    :supplementary_portraits, :conditions => {:primary => false}

  has_many    :portrait_assests, :through => :portraits
  has_one     :primary_portrait_asset, :through => :primary_portrait
  has_many    :supplementary_portrait_assets, :through => :supplementary_portraits

end

然后，如果你需要构建一个primary_portait_asset写一个实例方法

def build_primary_portrait_asset
  primary_portrait || build_primary_portrait
  primary_portrait.asset || primary_portrait.build_asset
end

Answer 2

为什么不这样做。

class Portrait
  belongs_to :portrait_subject
  belongs_to :asset

  ...
end

-

class PrimaryPortrait < Portrait
  ...
end

-

class SupplementaryPortraits < Portrait
  ...
end

-

class PortraitSubject
  has_one     :primary_portrait
  has_many    :supplementary_portraits
  ...
end

这更紧密地遵循导轨设计模式。您必须添加一个类型列。

Answer 3

我建议将其分为两个组合：

class PortraitSubject
  has_many    :portraits
  has_one     :primary_portrait, :class_name => "Portrait", :conditions => ['portraits.primary = ?', true]
  has_one     :primary_portrait_asset, :through => :primary_portrait, :source => :asset

  has_many    :supplementary_portraits, :class_name => "Portrait", :conditions => ['portraits.primary = ?', false]
  has_many     :supplementary_portrait_assets, :through => :supplementary_portraits, :source => :asset

  ...
end

然后，您可以使用subject.build_primary_portrait创建肖像模型，并通过subject.primary_portrait_asset访问其资源。

Rails has_one：通过。构建关联对象

3 个答案: