[Erp5-dev] count method in listbox

[Yoshinori Okuji]

I have added yet another attribute into ListBox. A "Count Method" is used to 
count the number of objects correctly. This feature is optional, so you do 
not have to it. Using this feature, however, is recommended for the 
performance improvement. It changes significantly if a module has many 
objects.

Here I describe how to use it:

- Add support for limit_expression into a list method. Add limit_expression 
into "Arguments", and add this into the SQL:

<dtml-if limit_expression>
LIMIT <dtml-var "limit_expression">
<dtml-else>
LIMIT 1000
</dtml-if>

You can change the default limit to whatever else you like.

- Set "Maximum rows to retrieve" to zero, so that ZMySQLDA won't add LIMIT 
automatically.

- Make a count method. For consistency, I recommend using the same Z SQL Mehod 
as the list method. You can use dtml conditionals to return different 
information, like this:

SELECT
  <dtml-if stat>
    SUM(stock.quantity) AS quantity
  <dtml-elif count>
    COUNT(DISTINCT catalog.id) AS count
  <dtml-else>
    DISTINCT
    <dtml-in "portal_catalog.getCatalogSearchResultKeys()"> <dtml-var 
sequence-item> <dtml-unless sequence-end>,</dtml-unless> </dtml-in>
    <dtml-if select_expression>, <dtml-var select_expression> </dtml-if>
  </dtml-if>
...

- If a ListBox uses portal_catalog for a list method, you can just specify 
portal_catalog for the count method as well. This results in calling 
portal_catalog.countResults after all.

YO
-- 
Yoshinori Okuji, Nexedi Research Director
Nexedi: Consulting and Development of Free / Open Source Software
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