Rails3 Arel访问自定义类

Question

我有一个自定义类,但我希望能够将它传递给Arel并让它解析其可查询部分.

module Custom
  class Item
    attr_accessor :name

    def initialize(name)
      self.name = name
    end
  end
end

custom_item = Custom::Item.new("Bill")
User.where(:name => custom_item)

有什么我可以在custom_item中定义,所以它会理解Arel想要它的名字吗？

目前我解决方法:

module Arel
  module Visitors
    class ToSql
      def visit_Custom_Item o
        "'#{o.name}'"
      end
    end
  end
end

Answer 1

我认为现在不可能.让我们试着找出原因.

当您尝试将自定义对象传递给where方法时,User.where(:name => custom_item)Arel尝试调用visit_YOUR_CLASS_NAME方法(https://github.com/rails/arel/blob/master/lib/arel/visitors/visitor.rb#L15)但它失败了.然后Arel尝试调用visit_+ object.class.ancestors.find {|klass| respond_to?(DISPATCH[klass], true)}但它再次失败,因为:

irb(main):001:0> class Foo
irb(main):002:1> end
=> nil
irb(main):003:0> foo = Foo.new
=> #<Foo:0x261edc0>
irb(main):004:0> foo.class.ancestors.map {|klass| p klass}
Foo
Object
Kernel
BasicObject
=> [Foo, Object, Kernel, BasicObject]

和Arel在此列表中没有任何此名称https://github.com/rails/arel/blob/master/lib/arel/visitors/to_sql.rb#L394:

alias :visit_ActiveSupport_Multibyte_Chars :quoted
alias :visit_ActiveSupport_StringInquirer  :quoted
alias :visit_BigDecimal                    :quoted
alias :visit_Class                         :quoted
alias :visit_Date                          :quoted
alias :visit_DateTime                      :quoted
alias :visit_FalseClass                    :quoted
alias :visit_Float                         :quoted
alias :visit_Hash                          :quoted
alias :visit_NilClass                      :quoted
alias :visit_String                        :quoted
alias :visit_Symbol                        :quoted
alias :visit_Time                          :quoted
alias :visit_TrueClass                     :quoted

实际上,我认为这不是一个非常有用的功能,但我已经问过Aaron Patterson,如果他愿意,我会尝试实现它.