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<?php |
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namespace izzum\statemachine; |
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/** |
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* EntityBuilder is an object that builds an entity (an application domain |
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* specific model) for a Context object so your statemachine can interact with your |
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* domain model. |
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* |
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* The entity returned is the application domain specific object that will be |
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* injected in the Rules and Commands for a specific statemachine (eg: Order) |
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* and can implement event handlers and callables. |
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* A typical statemachine would use a subclass of this builder. |
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* |
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* The Context can build the entity by using the associated Identity object of the |
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* Context. the entity can be obtained via the factory method EntityBuilder::getEntity(). |
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* |
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* Of course, a specific Rule or Command can just accept the Identifier directly |
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* and use the entity_id to generate the domain object itself. But this would |
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* also mean that the Rules and Commands will not be specific to the applications' |
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* problem domain but to that of the statemachine (and therefore possibly less |
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* reusable). It is therefore advisable to let a builder build your domain model. |
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* |
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* The Context instance is configured with this builder class by default. It can |
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* be configured with a subclass for your application domain if necessary (and the |
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* configuration can be done automatically by using a concrete instance of the AbstractFactory) |
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* |
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* This class implements caching of the domain model/entity returned. |
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* The builder is reusable for different statemachines (that have |
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* a different Entity by definition). The cache will be rebuilt whenever a new |
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* Identifier object is passed to the 'getEntity' method. |
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* |
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* This specific class (in contrast to subclasses) returns the Identifier itself instead of a domain model. |
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* This is useful because it allows us to test a lot of scenarios without side effects. |
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* It also allows us to use the Identifier object for our rules and commands, so |
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* you do not necessarily have to write your own entitybuilder. |
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* |
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* This is a prime candidate to be overriden by subclasses (if need be). |
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* Subclass this class and override the 'build' method to return a |
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* domain specific object of choice. The building of that domain object depends |
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* on the information in the Context, specifically the entity_id. |
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* |
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* the builder can be configured via dependency injection at creation time so |
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* the builder can make use of the injected data when it is called via 'getEntity'. |
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* |
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* An example of a builder would be an 'EntityBuilderOrder' class, |
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* which would be used for a statemachine that uses rules and commands to act |
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* upon an 'Order' object from your applation domain. |
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* |
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* @see Context::getEntity() |
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* @link https://en.wikipedia.org/wiki/Builder_pattern |
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* |
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* @author Rolf Vreijdenberger |
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* |
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*/ |
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class EntityBuilder { |
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/** |
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* a cached instance of the built entity object |
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* |
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* @var Object |
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*/ |
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protected $entity; |
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/** |
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* a cached instance of the used Identifier. |
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* |
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* @var Identifier |
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*/ |
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protected $identifier; |
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/** |
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* Gets an application domain specific model of choice, as implemented by a |
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* subclass. |
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* |
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* @param Identifier $identifier |
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* @param boolean $create_fresh_entity |
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* optional. if true, then a new instance is always created, |
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* else it might be cached if used for the same Identifier |
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* (performance). |
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* Since a statemachine might run multiple transitions in memory |
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* and alter the data in the persistence layer, |
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* there might be a need to refresh the entity (create it again) |
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* if the in memory object and the data |
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* in the persistence layer are not synchronized. this might |
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* cause rules or commands to act on |
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* in-memory data while it should use the persisted data. |
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* (an ORM should handle this automatically) |
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* |
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* @return Object an object of any type, depending on the statemachine. |
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* This object will be used by the Rule and Command that go with a |
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* certain statemachine. It will be injected in the constructor of |
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* the |
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* Rule and Command. |
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* It implements caching so we always get the same entity instance |
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* on |
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* each call of 'getEntity' with the same Context |
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* @see Context::getEntity() |
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* @throws Exception |
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*/ |
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final public function getEntity(Identifier $identifier, $create_fresh_entity = false) |
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{ |
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try { |
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// lazy loading with caching. |
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// we cache the context so we can be sure to provide |
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// a new reference to the entity when the builder is used on a new |
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// Identifier. |
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if ($this->entity === null || $this->identifier !== $identifier || $create_fresh_entity === true) { |
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// crate new entity and build cache |
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$this->entity = $this->build($identifier); |
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$this->identifier = $identifier; |
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} |
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return $this->entity; |
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} catch(Exception $e) { |
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// already a statemachine exception, just rethrow, it is logged |
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throw $e; |
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} catch(\Exception $e) { |
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// a non statemachine type exception, wrap it so it is logged and |
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// throw |
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$e = new Exception($e->getMessage(), Exception::BUILDER_FAILURE, $e); |
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throw $e; |
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} |
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} |
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/** |
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* the actual building function. |
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* Override this method to return an application specific domain model. |
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* |
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* In an overriden function it is possible to use the state of the concrete |
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* builder itself, which can be passed in via dependency injection at |
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* construction time, so we have additional information on how to build the |
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* domain object. |
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* |
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* @param Identifier $identifier |
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* @return Object an object of any type defined by the subclass |
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*/ |
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protected function build(Identifier $identifier) |
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{ |
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// the default implementation returns an Identifier, which holds an id |
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// that can be used in your rules and commands to build your domain |
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// logic or build your domain object. specialized builders return a domain |
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// model that will be accepted by your specialized rules/commands for |
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// your application. |
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return $identifier; |
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} |
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/** |
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* returns the string representation |
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* |
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* @return string |
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*/ |
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public function toString() |
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{ |
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return get_class($this); |
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} |
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/** |
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* returns the string representation |
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* |
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* @return string |
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*/ |
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public function __toString() |
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{ |
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return $this->toString(); |
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} |
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} |
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rolfvreijdenberger /
izzum-statemachine
