error handling - Ruby on Rails i18n - Want To Translate Custom Messages in Models

Question

I have attributes with special validation where I use the message clause to display a special message just for that validation. Here is one example:

validates :email, presence:   true, length: { maximum: 60 },
                format:     { with: valid_email_regex, message: "is not a valid email address format." },
                uniqueness: { case_sensitive: false } 

I would like to translate the message here but I am not sure how to do it.

I have seen examples where they type something like this: message: t("some_value_here"). I'm not sure about the designation. I tried something like this message: t(:bad_email). I did the following in my yaml file just to try something.

activemodel:
  errors:
    bad_email: "is not a valid email address format."

When I tried to access my Rails application I got the following error:

ActionView::Template::Error (undefined method `t' for #<Class:0x007fefc1b709e0>)

I also tried this in my yaml file:

activemodel:
  errors:
    user:
      bad_email: "is not a valid email address format."

I have been researching this off and on all day long. All I can find is to replace built-in error hashes like blank or empty. Is there a way for me to have custom error hashes and replace them in the model? At this point I cannot get the t to work as coded. My hope is that the problem is how I have my yaml file set up. I have seen varying versions of how to set this up. I am not sure if I should put this under activemodel or activerecord. I assumed activemodel since that is where the custom message is that I want to translate.

Any help would be appreciated. This is the last piece I need to figure out before launching my first translation of the application.

UPDATE 7/29/2013 7:30 pm CDT

bgates gave me a very good start with how to setup my model files to receive the custom message in the YAML file. However I ended up having to do the following setup in my yaml file for the custom messages to be found.

activerecord:
  errors: 
    models: 
      user: 
        attributes: 
          bio: 
            no_links: "cannot contain email addresses or website links (URLs)."
          email: 
            bad_email: "is not a valid email address format."
          username: 
            bad_username: "can only contain numbers and letters.  No special characters or spaces."

Answer 1

Use a symbol for the message:

validates :email, presence:   true, length: { maximum: 60 },
            format:     { with: valid_email_regex, message: :bad_email },
            uniqueness: { case_sensitive: false } 

then in the yaml file

[lang]:
  activerecord:
    errors:
      messages:
        bad_email: "just ain't right"

If there's a translation specific to this model, it will override the general one above:

[lang]:
  activerecord:
    errors:
      models:
        model_name: # or namespace/model_name
          attributes:
            email:
              bad_email: "model-specific message for invalid email"

If you write custom validations, add_error(:email, :bad_email) will do the lookup above, but errors[:email] << :bad_email will not.