This is my implementation of the "Specification" design pattern. It differs from the original one since i find it simpler and more straight forward.
It also allows the composition of multiple Specifications that takes in different types of parameters
The Goal of this pattern is to have separate classes of logic in order to do condition composition without rewriting and maintaining the conditions at different places.
Here is a detailed "how to" for thi package :
Create a class that implements the SpecificationInterface and that holds your logic :
Here is basic example of a list of specifications that checks differents things about products and customers
A class the checks if a product is available :
class IsProductAvaialble implement SpecificationInterface
{
protected $product;
protected $neededQuantity;
public function __construc(Product $product, $neededQuantity = 1)
{
$this->product = $product;
$this->neededQuantity = $neededQuantity;
}
public function isValid(): bool
{
//here your code logic that uses the data set in the construct and returns a boolean
}
}A class the checks if a product can be shipped to the customer :
class IsProductShipableForCustomer implement SpecificationInterface
{
protected $product;
protected $customer;
public function __construc(Product $product, Customer $customer)
{
$this->product = $product;
$this->customer = $customer;
}
public function isValid(): bool
{
//doing the logic to check if the product is avaialble in the customer's country
}
}A class the checks if a product is special (a special product is supposed to be (magically?) always in stock)
class IsASpecialProduct implement SpecificationInterface
{
protected $product;
public function __construc(Product $product)
{
$this->product = $product;
}
public function isValid(): bool
{
//doing the logic to check if the product is special
}
}A class that checks if a customer is not blacklisted
class IsCustomerBlackListed implement SpecificationInterface
{
protected $customer;
public function __construc(Customer $customer)
{
$this->customer = $customer;
}
public function isValid(): bool
{
//doing the logic to checks if the customer is banned
}
}One of the tree entry points of the specification pattern.
It Has to be used before any operator.
If used after an operator it will throw a WrongUsageException
Example :
$specification = (new Specification())->isSatisfiedBy(new IsProductAvaialble($product));
if ($specification->isValid()) {
...
}the second possible entry point of the specification pattern.
Checks if all the Specifications sent are Valid ones (equivalent to chaining and operators)
It Has to be used before any operator.
If used after an operator it will throw a WrongUsageException
Example :
$specification = (new Specification())->isSatisfiedByAll(
new IsProductAvaialble($product),
new IsProductShipableForCustome($product, $customer)
);
if ($specification->isValid()) {
...
}the third and last possible starting point of the specification pattern.
Checks if one of the Specifications sent is a Valid one (equivalent to chaining or operators)
It Has to be used before any operator.
If used after an operator it will throw a WrongUsageException
Example :
$specification = (new Specification())->isSatisfiedByAny(
new IsProductAvaialble($product),
new IsASpecialProduct($product)
);
if ($specification->isValid()) {
...
}adds an '&&' condition to the previously set specifications
It can not be used first or else it will throw a WrongUsageException
Example :
$specification = (new Specification())
->isSatisfiedBy(new IsProductAvaialble($product))
->and(new IsProductShipableForCustomer($product, $customer))
...
;
if ($specification->isValid()) {
...
}adds an '&& !' condition to the previously set specifications
It can not be used first or else it will throw a WrongUsageException
Example :
$specification = (new Specification())
->isSatisfiedBy(new IsProductAvaialble($product))
->and(new IsProductShipableForCustomer($product, $customer))
->andNot(new IsCustomerBlackListed($customer)
...
;
if ($specification->isValid()) {
...
}adds an '||' condition to the previously set specifications
It can not be used first or else it will throw a WrongUsageException
Example :
$specification = (new Specification())
->isSatisfiedBy(new IsProductAvaialble($product))
->or(new IsASpecialProduc($product))
...
;
if ($specification->isValid()) {
...
}adds an '|| !' condition to the previously set specifications
It can not be used first or else it will throw a WrongUsageException
Example :
$specification = (new Specification())
->isSatisfiedBy(new IsProductAvaialble($product))
->orNot(new IsASpecialProduc($product))
;
if ($specification->isValid()) {
...
}adds a 'xor' condition to the previously set specifications
It can not be used first or else it will throw a WrongUsageException
Example :
$specification = (new Specification())
->isSatisfiedBy(new IsProductAvaialble($product))
->xor(new IsASpecialProduc($product))
;
if ($specification->isValid()) {
...
}adds a 'xor !' condition to the previously set specifications
It can not be used first or else it will throw a WrongUsageException
Example :
$specification = (new Specification())
->isSatisfiedBy(new IsProductAvaialble($product))
->xorNot(new IsASpecialProduc($product))
;
if ($specification->isValid()) {
...
}The specifications can be composed :
Example:
$specification = (new Specification())
->isSatisfiedBy(new IsProductShipableForCustomer($product, $customer))
->and(
(new Specification())
->isSatisfiedBy(new IsProductAvaialble($product))
->or(new IsASpecialProduct($product))
)
;
if ($specification->isValid()) {
...
}