[Zope] Dynamic Reference, mixing ZOPE and SQL

30 Jan 2004

      I have a sequence of code that is monstrously inefficient and am
looking for help. I am storing the id tag of an ExtFile object in my
sql database along with other information and am now creating a page
that displays info from the database record by record. For each
record displayed, I also want to pull the file size from the Zope
side of things.

The method which works is something like this:

    <dtml-in my_query>
      <dtml-comment>
        query returns file_id amongst other values
      </dtml-comment>
      <dtml-with files>
        <dtml-in "objectValues(['ExtFile'])">
          <dtml-if "id == file_id">
            <dtml-var size>
          </dtml-if>
        </dtml-in>
      </dtml-with>
    </dtml-in>

With a 1000+ ExtFile objects in the "files" folder, the search is ok
for just one record being displayed; however, if this page is
displaying all 1000+ files based on the SQL records, then for each
SQL record returned it is iterating through the entire contents of
my files folder, and is very slow to resolve.

What I am looking for is a way to say:

    <dtml-in my_query>
      <dtml-comment>
        query returns file_id amongst other values
      </dtml-comment>
      <dtml-var files.file_id.size>  //where file_id is a dynamic ref
                                     // not the id itself
    </dtml-in>

However, I don't know a good method for doing a dynamic reference
here, such as the following which fails:

    <dtml-in my_query>
      <dtml-comment>
        query returns file_id amongst other values
      </dtml-comment>
      <dtml-with files>
        <dtml-in "objectValues(['ExtFile'])._['file_id']">
          <dtml-var size>
        </dtml-in>
      </dtml-with>
    </dtml-in>

I am just extrapolating from things like using "sequence-item" in an
expression changes it over to "_['sequence-item']". Not even sure
the dtml-in would work the way I want, but the idea is there. Maybe
to effectively use something like this to reference an object I
explicitly know:

    <dtml-in my_query>
      <dtml-comment>
        query returns file_id amongst other values
      </dtml-comment>
      <dtml-var "files._['file_id'].size">
    </dtml-in>

The above approach throws unauthorized exceptions, so obviously not
the right way to go about it.

Anyone know the correct syntax for achieving this both inside a
python expression and/or as a direct dtml expression?

Thanks,
-- 
Ryan T. Bard
Webmaster/Software Developer
Department of Medical Education
University of Miami School of Medicine
Office: (305) 243-3273

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