如何在ruby on rails中使用instance_eval覆盖哈希常量

Question

如何使用插件中的instance_eval覆盖类中的常量这是我要覆盖的常量

```

类MessageTemplate

 TEMPLATE_KEYS = {

:guardian=>{
  :guardian_full_name=>"guardian_full_name",
  :guardian_first_name=>"guardian_first_name",
  :guardian_last_name=>"guardian_last_name",
  :ward_full_name=>"ward_full_name",
  :guardians_relation=>"guardians_relation",
  :ward_batch_name=>"ward_batch_name",
  :ward_admission_number=>"ward_admission_number",
  :guardian_email=>"guardian_email",
  :guardian_mobile_phone_no=>"guardian_mobile_phone_no"
}

}结束

I wand to add below values to the above constant from a plugin in ruby on rails
this is the way I tried and failed

模块IndepthEinvoice

     module MessageTemplate
def self.included(base)
  base.instance_eval do
    self.TEMPLATE_KEYS = {
      :guardian=>{
          :payment_link=>"payment_link",
          :ward_balance_fee=>"ward_balance_fee"
      }
  }
  end
end

Answer 1

修改重复项或克隆而不是常量

Ruby实际上不会阻止您重新分配常量；通常只会发出警告。尽管如此，通常还是故意修改常量被认为是不好的形式。相反，您应该使用Hash#merge或Hash#merge!将所做的更改存储在本地哈希对象中。例如：

TEMPLATE_KEYS = {
  guardian: {
    guardian_full_name:       "guardian_full_name",
    guardian_first_name:      "guardian_first_name",
    guardian_last_name:       "guardian_last_name",
    ward_full_name:           "ward_full_name",
    guardians_relation:       "guardians_relation",
    ward_batch_name:          "ward_batch_name",
    ward_admission_number:    "ward_admission_number",
    guardian_email:           "guardian_email",
    guardian_mobile_phone_no: "guardian_mobile_phone_no",
  }
}

# make a copy of your TEMPLATE_KEYS constant
@my_template = TEMPLATE_KEYS.dup

# merge your modifications into an instance variable
@my_template[:guardian].merge!(
  {
    payment_link:     "payment_link",
    ward_balance_fee: "ward_balance_fee",
  }
)

@my_template.dig :guardian, :payment_link
#=> "payment_link"

当然，还有其他方法可以做到这一点，有些方法比其他方法更优雅。但是，该原理是合理的，并且绝对比尝试直接修改该常量好，这可能会对您的应用程序产生意想不到的后果。