Filter Chains
Often multiple filters should be applied to some value in a particular order. For example, a
login form accepts a username that should be only lowercase, alphabetic characters.
Zend_Filter provides a simple method by which filters may be chained
together. The following code illustrates how to chain together two filters for the submitted
username:
// Create a filter chain and add filters to the chain
$filterChain = new Zend_Filter();
$filterChain->addFilter(new Zend_Filter_Alpha())
->addFilter(new Zend_Filter_StringToLower());
// Filter the username
$username = $filterChain->filter($_POST['username']);
Filters are run in the order they were added to
Zend_Filter. In the
above example, the username is first removed of any non-alphabetic characters, and then any
uppercase characters are converted to lowercase.
Any object that implements Zend_Filter_Interface may be used in a
filter chain.
Changing filter chain order
Since 1.10, the Zend_Filter chain also
supports altering the chain by prepending or appending filters. For
example, the next piece of code does exactly the same as the other
username filter chain example:
// Create a filter chain and add filters to the chain
$filterChain = new Zend_Filter();
// this filter will be appended to the filter chain
$filterChain->appendFilter(new Zend_Filter_StringToLower());
// this filter will be prepended at the beginning of the filter chain.
$filterChain->prependFilter(new Zend_Filter_Alpha());
// Filter the username
$username = $filterChain->filter($_POST['username']);