Difference between revisions of "DPL:Manual - DPL parameters: Other parameters"

Revision as of 13:36, 27 April 2009

goal

Syntax:

goal=pages | categories

Explanation:

Default is 'pages', which means that DPL produces a list of pages. And this is exactly what the name DPL promises.

If you set the goal parameter to 'categories' the list of pages will still be produced but you won´t see it. Instead it will be used to calculate a unique ordered list of all categories these pages belong to.

This allows you to ask a question like: Given all pages that are member of category X with a title matching "y%" and which use template "Z": to which categories do these pages belong?

One of the more useful applications would be question like: "To which categories do the pages belong which contain a reference to the current page?"

The output of "goal=categories" is technically a list of pages of type category. This means that you can use all DPL formatting options (mode=userformat, listseparators, columns etc.) and pseudo variables (%TITLE%, %PAGE%) to customise the layout of your report.

Technical Note:

Due to some limitations in MySQL it is currently not possible to restrict the intermediate result set of pages to a certain maximum (using the LIMIT clause). In addition the generated SQL code is not in all cases optimal (as its structure provides for complex selection criteria and therefore is unnecessarily complex in simple cases). So be careful and apply precise selection criteria.

allowcachedresults

Syntax:

allowcachedresults=true | false | yes+warn

Explanation:

Default is FALSE, so normally DPL will disable the parser cache before it produces a result. Disabling the cache produces some extra server load but guarantees always correct results.

So, if you do not use this parameter you will always get a result which is based on the latest changes made on any articles. But in many cases you could have gotten the same result with using less server resources!

If you set 'allowcachedresults=true', the parser cache will be used. That means, your results might be a little bit outdated (usually one hour or so). But there are less resources used on the server side. You might want to experiment with that parameter and check the size of load reduction (i.e. gain in term of response time).

If you allow cached results you can still enforce DPL to produce a correct result via using "&action=purge" in the command line.

'yes+warn' will use the cache; in addition the result will contain a warning indicating that the result may be out-dated. This is achieved by including the template DPL Cache Warning into the result header. It is up to you to provide a useful text under that name, see e.g. Template:DPL Cache Warning.

reset

Syntax:

reset=keyword,.., where keyword is one of:

• categories
• templates
• images
• links
• all — a synonym for all of the above

The output of a DPL statement typically creates links to all pages which are part of the result set. The inclusion of contents from other pages via DPL (using 'include') normally has the consequence

• that the page containing the DPL query becomes part of the categories of the transcluded page
• that it shares ('adopts') their use of templates
• that it shares their references to images
• that it shares their references to other articles.

In some cases this may be useful. But in many cases this is not wanted. Especially when you use DPL to create a printable document which contains the full text of other articles you will probably not want to duplicate all links, template uses etc. of those articles.

The reset parameter will suppress all or some of the effects described above.

There are some subtle differences here depending on the mode in which you use DPL. These differences affect the question how links, and categories etc. are treated which are direct part of the document containing the DPL query. Example:

 [[Category:Q Cat]] linking to [[Q Link]] and showing [[Image:Q Image]] and using {{Q Template}}
 ... DPL query which includes contents from other articles.
     assuming that this contents contains links and images, 
              that it uses templates and thatthe articles are part of one or more categories
     RESET statement at the end of the DPL query with one or more of 'categories,templates,images,links'
 ...

In parser extension mode (DPL tag like <DPL>):

reset=categories

will ignore categories of included contents but keep 'own' categories like 'Q Cat'.

reset=images

will throw away references to images contained in included contents but keep 'own' images like 'Q Image'.

reset=templates

will ignore templates used in included contents but keep 'own' template usage ('Q Template').

reset=links

will throw away all references to other pages, i.e. links contained in included contents and links like 'Q Link' will be ignored. This means that all links can be used in the normal "FORWARD" way, but no "BACKLINKS" are available for them.

If you want to avoid the above described effect of reset on your 'own' links you can use eliminate. But you should know that eliminate is rather expensive in terms of computer power as it does a second parse for all included contents.

In parser fuction mode ({{#DPL:....}}):

reset=categories

will ignore all categories

reset=images

will throw away all references to images

reset=templates

will ignore all template invocations

reset=links

will throw away all references to other pages

As you see, using reset in parser function mode will clear everything regardless whether it comes from included contents or whether it is direct part of the document containing the DPL query.

If you want to avoid the above described effect of reset, you can use eliminate. But you should know that eliminate is rather expensive in terms of computing power as it does a second parse for all included contents. The extra parser step is conducted as soon as you specify eliminate. In terms of extra processing needed it does not make a difference whether you specify one or more arguments for the 'eliminate' command.

If you have more than one DPL query in a document the effects will depend on the exact mode (parser extension or parser function mode), on the sequence of the statements and on the presence of 'reset' or 'eliminate' statements in each of the queries and on their individual arguments. As this is a very rare case we only give a simple rule of thumb here: Once you have used 'reset' in parser function mode or 'reset=links' in parser extension mode the effect of these statements will dominate the rest.

eliminate

Syntax:

eliminate=keyword,..

Where keyword is one of:

• categories
• templates
• images
• links
• all — a synonym for all of the above

The output of a DPL statement typically creates links to all pages which are part of the result set. The inclusion of contents from other pages via DPL (using include) normally has these consequences:

• the page containing the DPL query becomes part of the categories of the transcluded page
• shares ('adopts') their use of templates
• shares their references to images
• shares their references to other articles

In some cases this may be useful. But in many cases this is not wanted. Especially when you use DPL to create a printable document which contains the full text of other articles you will probably not want to duplicate all links, template uses etc. of those articles.

The eliminate parameter will suppress all or some of the effects described above.

For further explanation see reset.

Please note that the use of eliminate needs a considerable amount of extra computing power as it performs a second parser step for each included document.

debug

Syntax:

debug=n, where n is one of:

• 0 — silent mode, shows nothing
• 1 — quiet mode, shows (fatal) errors
• 2 — default mode, like 1 + shows warnings; — (default)
• 3 — verbose mode, like 2 + shows SQL query.
• 4 — for internal use only
• 5 — show Wiki text output from DPL instead of parsed wiki text

If you use debug param but not in first position in the DPL element, the new debug settings are not applied before all previous parameters have been parsed and checked. This will generate a warning for debug=2 and above.

Example:

<DPL>
  namespace=Media
  debug=0
  namespace=Special
</DPL>

This list will output the error for the first namespace: Media is not a valid namespace value (pseudo-namespace). Assuming you haven't changed the default debug value (2), you will also get a warning: debug=1 is not input first (before namespace=Media). So it did not apply to namespace=Media but only to what's after. Indeed, you won't get the warning for the second namespace (Special) since debug=0 changed debug settings to silent mode.

DPL debug messages are translatable in DynamicPageList2.i18n.php. See also #Internationalization.

'debug=1' will suppress warning messages (e.g. if the result set of a DPL query is empty). As an alternative, you can use the suppresserrors statement.