Ruby-on-rails Rails has_many 具有动态条件

Rails has_many with dynamic conditions

提问by Fabiano Soriani

What I want is to create a Model that connects with another using a has_many association in a dynamic way, without the foreign key like this:

我想要的是创建一个模型，该模型以动态方式使用 has_many 关联与另一个连接，而没有像这样的外键：

has_many :faixas_aliquotas, :class_name => 'Fiscal::FaixaAliquota',
            :conditions => ["regra_fiscal = ?", ( lambda { return self.regra_fiscal } ) ]

But I get the error:

但我收到错误：

: SELECT * FROM "fis_faixa_aliquota" WHERE ("fis_faixa_aliquota".situacao_fiscal_id = 1
AND (regra_fiscal = E'--- !ruby/object:Proc {}'))

Is this possible?

这可能吗？

回答by Chirantan

Rails 4+ way (Thanks to Thomas who answered this below):

Rails 4+ 方式（感谢 Thomas 在下面回答了这个问题）：

has_many :faixas_aliquotas, -> (object) { 
           where("regra_fiscal = ?", object.regra_fiscal)
         },
         :class_name => 'Fiscal::FaixaAliquota'

Rails 3.1+ way:

Rails 3.1+ 方式：

has_many :faixas_aliquotas, :class_name => 'Fiscal::FaixaAliquota',
         :conditions => proc { "regra_fiscal = #{self.regra_fiscal}" }

Rails 3 and below:

Rails 3 及以下：

has_many :faixas_aliquotas, :class_name => 'Fiscal::FaixaAliquota',
         :conditions => ['regra_fiscal = #{self.regra_fiscal}']

No. This is not a mistake. The conditions are specified in single quotes and still contains the code #{self.regra_fiscal}. When the conditions clause is evaulated, the regra_fiscal method will be called on the object of self(whatever the class is). Putting double quotes will not work.

不。这不是错误。条件用单引号指定，但仍包含代码#{self.regra_fiscal}。当评估条件子句时，将在self（无论类是什么）的对象上调用 regra_fiscal 方法。放双引号是行不通的。

I hope this is what you are looking for.

我希望这就是你正在寻找的。

回答by Thomas

Rails 4+ way:

Rails 4+ 方式：

has_many :faixas_aliquotas, 
         -> (object){ where("regra_fiscal = ?", object.regra_fiscal)},  
         :class_name => 'Fiscal::FaixaAliquota'

回答by Chirantan

There is another kind of solution. However, this wont be the default scope.

还有另一种解决方案。但是，这不会是默认范围。

has_many :faixas_aliquotas, :class_name => 'Fiscal::FaixaAliquota' do 
  def filter(situacao_fiscal)
    find(:all, :conditions => {:regra_fiscal => situacao_fiscal.regra_fiscal})
  end
end

This way you would be able to do

这样你就可以做到

situacao_fiscal.faixas_aliquotas.filter(situacao_fiscal)

I am not sure if this is elegant and something that would solve your problem. There may be better ways of doing this.

我不确定这是否优雅并且可以解决您的问题。可能有更好的方法来做到这一点。

回答by GeoffreyHervet

Rails 4+another way:

Rails 4+ 的另一种方式：

has_many :faixas_aliquotas, -> (object){ where(regra_fiscal: object.regra_fiscal) }, :class_name => 'Fiscal::FaixaAliquota'

回答by Amala

In Rails 3.1 need to use proc, Proc.new { "field = #{self.send(:other_field)}" }

在 Rails 3.1 中需要使用 proc, Proc.new { "field = #{self.send(:other_field)}" }

回答by bayfieldcoder

In Rails 3.1 you can use Proc.new for your conditions. as stated by @Amala, but instead generate a hash like this:

在 Rails 3.1 中，您可以将 Proc.new 用于您的条件。如@Amala 所述，而是生成这样的哈希：

has_many :faixas_aliquotas, :class_name => 'Fiscal::FaixaAliquota',
   :conditions => {:regra_fiscal => Proc.new { {:regra_fiscal => self.regra_fiscal} }

The benefit of this approach is that if you do object.faixas_aliquotas.build, the newly created object will automatically have the same regra_fiscalattribute as the parent.

这种方法的好处是，如果这样做object.faixas_aliquotas.build，新创建的对象将自动具有与regra_fiscal父对象相同的属性。