Rails has_many with dynamic conditions

Question

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:

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

But I get the error:

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

Is this possible?

Answer 1

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

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

Rails 3.1+ way:

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

Rails 3 and below:

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.

I hope this is what you are looking for.