A Polite Request - Zope

Take a look at this next example, which demonstrates how the <dtml-with> tag can be used to work around the problems encountered in the previous example.

<b>
<dtml-with REQUEST only>
<dtml-if id>The value of "id" is <dtml-var 
id><br></dtml-if> <dtml-if
icon>The value of "icon" is <dtml-var icon><br></dtml-if> 
<dtml-if
me>The value of "me" is <dtml-var me><br></dtml-if> </dtml-with> 
</b>

Now, take a look at the output:

The value of "id" is 1234
The value of "icon" is folder
The value of "me" is 
John 

How did this work? The <dtml-with> tag - it is used to push a object to the top of the DTML namespace. As a result, Zope will look for all the variables in this object first.

<dtml-with REQUEST only>

The above statement pushes the REQUEST object to the top of the namespace stack. This object consists of the CGI environment variables, cookies and form data sent using the GET and POST methods.

For a quick glimpse into this object, create a new DTML Document with the following code.

<dtml-var REQUEST>

And when you view the output of this script, you'll see exactly what the REQUEST object contains.

The additional "only" attribute in the call to <dtml-with> tells Zope that it should not look beyond the REQUEST object for these values. Why bother with this extra tag? Consider what will happen if you don't pass a value for the "id" parameter - once Zope checks the REQUEST object and fails to find a value for this variable, it will proceed down the namespace stack to see if a value exists anywhere else. And we know it does - which could lead to unexpected results. The "only" attribute is the only (pardon the pun) way to ensure that this does not happen.

<dtml-if id>The value of "id" is <dtml-var id><br></dtml-if> <dtml-if
icon>The 
value of "icon" is <dtml-var icon><br></dtml-if> <dtml-if
me>The value 
of "me" is <dtml-var me><br></dtml-if>

The rest of the code checks to see whether the named variable exists in the REQUEST object, and only displays the corresponding line of output if it does. Again, this is a good way to avoid the unexpected, and to prevent bugs creeping in.

>>> More Zope Articles          >>> More By Harish Kamath, (c) Melonfire

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