Filter cache¶

Once parsed a filter is stored into session. This is not related to the session storage mechanism mentioned above. It is used automatically so that values from a previous parsing are preserved. This is useful if you want to change just one value in a filter and preserve the others.

The drawback – as with any caching mechanism – is that this cache sometimes needs to be cleared. For example, if the filter relates to a search form, the filter cache must be cleared when a new search is performed. This can be achieved by sending "clear_cache = 1" either as a GET or POST parameter. In the example of a search form, this could be a hidden field in the search form.

There's also a possibility to clear the cache more selectively, for a single value, using a configuration like:

tt_news_cat.uid = vars:showUid // \clear_cache

In this example, if there's no showUid to be found in the vars, the value returned by the parser will be \clear_cache. The Data Filter will act upon this and remove that value from the session cache.