[Zope] Re: Can't compare apples to apples. (document_id != id_of_my_document)

[Steve Alexander]

T.J. Mannos wrote:
>
> I have a DTML document called "apples".
>
> A call to <dtml-var document_id> gives the string "apples"
>
> However, a <dtml-if "document_id == 'apples'"> returns false.  Am I missing
> something?  I've tried _.str(document_id) and even
> _.string.strip(_.str(document_id)).

The tag <dtml-var document_id> gets a value for document_id, and looks
to see if it is callable. If so, it calls it and returns the result of
calling it. If not, it just returns it. This is a feature of <dtml-var
name="whatever">, which is another way of writing <dtml-var whatever>.

However, when you use an expression, such as you are doing in the
dtml-if tag, you are writing in Python, and you need to call an object
if it ought to be called.
An expression is something like <dtml-var "expression"> or <dtml-var
expr="expression>, which are equivalent. The same goes for <dtml-if
"expression">.

In your case, you might find that this works:

<dtml-if "document_id() == 'apples'">

Or perhaps this:

<dtml-if "document_id(_.None, _) == 'apples'">

The reason is that ids ought always to be simple string objects, but
some aren't. There are lots of legacy programs that rely on some ids
being methods, so the odd cases won't be changed for a while yet.

The general answer is to use a special function that calls the value if
it is callable.

You have a choice here. These are equivalent.

<dtml-if "_['document_id'] == 'apples'">

<dtml-if "_.getitem('document_id', 1) == 'apples'">


--
Steve Alexander
Software Engineer
Cat-Box limited
http://www.cat-box.net