Re: Using validators

Mike Orr wrote:
> I've got a few questions about validators.  The FormEncode docs are
> great for explaining how the validators work, but they don't say which
> ones are best for various input controls.  I've also got a couple
> complex situations.
> 
> 1) What's the right validator for a checkbox?  I'm using
> StringBoolean(), and it says "Missing value" unless the box is
> checked.  Which is great if the box is labelled "Transfer $1,000,000
> into Mike's bank account", but not for other things.

They should have if_missing=False added.

> 2) Submit buttons should be String?  And hidden values too?

Generally I don't name my submit buttons.  If you have ignore/remove 
hidden set on the schema, they can be nothing (and the value is just 
removed).  Otherwise string.

> 3) I notice String returns unicode, at least in Pylons with the form
> set to utf-8.  Hopefully it will remain that way.

Yes.  Perhaps confusingly Unicode does encoding/decoding (though it 
should be safe given unicode input, but it would still produce str output).

> 4) My forms have a second submit button labeled Cancel, which simply
> does a redirect to an appropriate place.  I could make this a
> hyperlink but would like to keep it a button.  I need to bypass all
> the other validators if Cancel is pressed because their value doesn't
> matter.  How would I set this up?

You'd have to check this up-front before doing the validation.  You 
could do:

<button onclick="location.href='location'; return false">Cancel</button>

The degradation isn't great, though.  I think if you add a name 
attribute you could avoid the submit on cancel, but without Javascript 
still test the submission.

> 5) I need to make an attachment widget that's simply an upload control
> if there's no existing attachment.  But if there is an existing
> attachment, it needs to show its info and thumbnail, radio buttons for
> "keep", "replace with...", "delete", and an upload control for
> replacement.  In Quixote I used a composite widget that returned a
> tuple.  How would I make a validator for this?  How would I set up the
> dict-dot feature for:
> 
>     fieldname.file => file upload control
>     fieldname.action => radiobutton value ("keep", "replace",
> "delete"), or hidden value ("add")

A composite widget is a schema.  As long as you name them these names 
and use variabledecode, then "fieldname" will be a dictionary.  So you'd 
have:

class MyForm(Schema):
     class fieldname(Schema):
         file = File()
         action = String()

You'll get back {'fieldname': {'file': value, 'action': value}}.  If you 
want to make something reusable you can create all this in a subclass of 
Schema, overriding _to_python and _from_python.  Some of the 
file-related validators in FormEncode are meant to be used much like 
this.  I could go into more detail later if you want, but can't at the 
moment.

   Ian

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