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libphutil/src/symbols/PhutilClassMapQuery.php
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PhutilClassMapQuery.php
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<?php
/**
* Load a map of concrete subclasses of some abstract parent class.
*
* libphutil is extensively modular through runtime introspection of class
* maps. This method makes querying class maps easier.
*
* There are several common patterns used with modular class maps:
*
* - A `getUniqueKey()` method which returns a unique scalar key identifying
* the class.
* - An `expandVariants()` method which potentially returns multiple
* instances of the class with different configurations.
* - A `getSortName()` method which sorts results.
* - Caching of the map.
*
* This class provides support for these mechanisms.
*
* Using the unique key mechanism with @{method:setUniqueMethod} allows you to
* use a more human-readable, storage-friendly key to identify objects, allows
* classes to be freely renamed, and enables variant expansion.
*
* Using the expansion mechanism with @{method:setExpandMethod} allows you to
* have multiple similar modular instances, or configuration-driven instances.
*
* Even if they have no immediate need for either mechanism, class maps should
* generally provide unique keys in their initial design so they are more
* flexible later on. Adding unique keys later can require database migrations,
* while adding an expansion mechanism is trivial if a class map already has
* unique keys.
*
* This class automatically caches class maps and does not need to be wrapped
* in caching logic.
*
* @task config Configuring the Query
* @task exec Executing the Query
* @task cache Managing the Map Cache
*/
final class PhutilClassMapQuery extends Phobject {
private $ancestorClass;
private $expandMethod;
private $uniqueMethod;
private $sortMethod;
// NOTE: If you add more configurable properties here, make sure that
// cache key construction in getCacheKey() is updated properly.
private static $cache = array();
/* -( Configuring the Query )---------------------------------------------- */
/**
* Set the ancestor class name to load the concrete descendants of.
*
* @param string Ancestor class name.
* @return this
* @task config
*/
public function setAncestorClass($class) {
$this->ancestorClass = $class;
return $this;
}
/**
* Provide a method to select a unique key for each instance.
*
* If you provide a method here, the map will be keyed with these values,
* instead of with class names. Exceptions will be raised if entries are
* not unique.
*
* You must provide a method here to use @{method:setExpandMethod}.
*
* @param string Name of the unique key method.
* @return this
* @task config
*/
public function setUniqueMethod($unique_method) {
$this->uniqueMethod = $unique_method;
return $this;
}
/**
* Provide a method to expand each concrete subclass into available instances.
*
* With some class maps, each class is allowed to provide multiple entries
* in the map by returning alternatives from some method with a default
* implementation like this:
*
* public function generateVariants() {
* return array($this);
* }
*
* For example, a "color" class may really generate and configure several
* instances in the final class map:
*
* public function generateVariants() {
* return array(
* self::newColor('red'),
* self::newColor('green'),
* self::newColor('blue'),
* );
* }
*
* This allows multiple entires in the final map to share an entire
* implementation, rather than requiring that they each have their own unique
* subclass.
*
* This pattern is most useful if several variants are nearly identical (so
* the stub subclasses would be essentially empty) or the available variants
* are driven by configuration.
*
* If a class map uses this pattern, it must also provide a unique key for
* each instance with @{method:setUniqueMethod}.
*
* @param string Name of the expansion method.
* @return this
* @task config
*/
public function setExpandMethod($expand_method) {
$this->expandMethod = $expand_method;
return $this;
}
/**
* Provide a method to sort the final map.
*
* The map will be sorted using @{function:msort} and passing this method
* name.
*
* @param string Name of the sorting method.
* @return this
* @task config
*/
public function setSortMethod($sort_method) {
$this->sortMethod = $sort_method;
return $this;
}
/* -( Executing the Query )------------------------------------------------ */
/**
* Execute the query as configured.
*
* @return map<string, object> Realized class map.
* @task exec
*/
public function execute() {
$cache_key = $this->getCacheKey();
if (!isset(self::$cache[$cache_key])) {
self::$cache[$cache_key] = $this->loadMap();
}
return self::$cache[$cache_key];
}
/**
* Generate the core query results.
*
* This method is used to fill the cache.
*
* @return map<string, object> Realized class map.
* @task exec
*/
private function loadMap() {
$ancestor = $this->ancestorClass;
if (!strlen($ancestor)) {
throw new PhutilInvalidStateException('setAncestorClass');
}
if (!class_exists($ancestor)) {
throw new Exception(
pht(
'Trying to execute a class map query for descendants of class '.
'"%s", but no such class exists.',
$ancestor));
}
$expand = $this->expandMethod;
$unique = $this->uniqueMethod;
$sort = $this->sortMethod;
if (strlen($expand)) {
if (!strlen($unique)) {
throw new Exception(
pht(
'Trying to execute a class map query for descendants of class '.
'"%s", but the query specifies an "expand method" ("%s") without '.
'specifying a "unique method". Class maps which support expansion '.
'must have unique keys.',
$ancestor,
$expand));
}
}
$objects = id(new PhutilSymbolLoader())
->setAncestorClass($ancestor)
->loadObjects();
// Apply the "expand" mechanism, if it is configured.
if (strlen($expand)) {
$list = array();
foreach ($objects as $object) {
foreach (call_user_func(array($object, $expand)) as $instance) {
$list[] = $instance;
}
}
} else {
$list = $objects;
}
// Apply the "unique" mechanism, if it is configured.
if (strlen($unique)) {
$map = array();
foreach ($list as $object) {
$key = call_user_func(array($object, $unique));
if (empty($map[$key])) {
$map[$key] = $object;
continue;
}
throw new Exception(
pht(
'Two objects (of classes "%s" and "%s", descendants of ancestor '.
'class "%s") returned the same key from "%s" ("%s"), but each '.
'object in this class map must be identified by a unique key.',
get_class($object),
get_class($map[$key]),
$ancestor,
$unique.'()',
$key));
}
} else {
$map = $list;
}
// Apply the "sort" mechanism, if it is configured.
if (strlen($sort)) {
$map = msort($map, $sort);
}
return $map;
}
/* -( Managing the Map Cache )--------------------------------------------- */
/**
* Return a cache key for this query.
*
* @return string Cache key.
* @task cache
*/
private function getCacheKey() {
$parts = array(
$this->ancestorClass,
$this->uniqueMethod,
$this->expandMethod,
$this->sortMethod,
);
return implode(':', $parts);
}
}
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