Protecting fields from being changed

Hi all,

I am familiar with attr_accessible. But lately I have realised that
it doesnt do exactly what I want it to do.

Once a user is created on the system, I want to prevent the person
from changing their username.

I need username to be accessible on create... but after that I need it
to be protected.

Similarly - passwords need to be protected malicious form submits. I
don't want peope to be able to change their password in a sneaky way
when, say, they submit a form to change their address.

Instead, passwords should only be changed after they submit a very
paticular form, and after they confirm the change through email.

Are there any ideas on how to lock down certain values in a model
after its initial creation?

thanks!

you could do a before_update, or try this:

http://locusfoc.us/2007/2/1/validates_unchangeable-plugin

with before_update

is the idea that i check the submitted fields and throw an exception
if a protected field is given for an existing record?

is there a clean way to do this already explored?

This sounds to me like you're expecting that an update via ActiveRecord will automatically write any data it recieves from a form. So, if you have a form that is intended to update a user's name, and they copy the HTML, then add a password field that they collected from the original account create form, then submit that version, you're suspicious that the password data actually makes it all the way through to the database. Is that what you're worried about?

Me too. :slight_smile: I'm new to Rails, and haven't yet figured out what it has to protect against this situation, but in my own framework, my form processing had a required attribute which is an explicit list of allowed inputs by name. SQL was generated based on which inputs were submitted, but no matter what gets sent by POST or GET, and no matter even if you handed over the entire params array, the SQL generator would only allow those explicitly named inputs to become part of the query.

IMO, it's an essential part of input validation. Accept only what you want to accept applies to the actual field count in addition to date/format per field. To me the protection you're looking for doesn't belong as a state of attribute in the model, it belongs at the poing of filtering the form to start with. That's how you achieve fields being changed by "a very particular form."

I would suspect Rails has some mechanism for this input filtering, but I haven't gotten that far yet.

-- gw

I haven't tested this, but i think for the fields /columns you want
write-once, you just return false/nil.

Also, there's this, and attr_readonly, but I haven't figured out how
to use it:
http://constancy.rubyforge.org/
http://dev.rubyonrails.org/ticket/6896

BTW, this is a pretty common requirement, dozens of blogs. Search for
"read-only", "write-once", "write-protected" "constant" fields/
columns/ objects/models etc.

Any methods that are declared as protected will not be updated by
update_attributes. You must set them explicitly using the attributes
setter method. This doesn’t prevent them from being changed, but it
does prevent form data sent to update_attributes from changing them.
Hope this helps.

-Bill

Greg Willits wrote: