Webmozart Expression
Latest release: 1.0.0
PHP >= 5.3.9
This library implements the Specification Pattern for PHP. You can use it to
easily filter results of your domain services by evaluating logical expressions.
Conversely to rulerz, this library focuses on providing a usable and efficient
PHP API first. An expression language that converts string expressions into
Expression instances can be built on top, but is not included in the current
release.
Visitors can be implemented that convert Expression objects into Doctrine
queries and similar objects.
Installation
Use Composer to install the package:
$ composer require webmozart/expression
Basic Usage
Use the Expression interface in finder methods of your service classes:
use Webmozart\Expression\Expression;
interface PersonRepository
{
public function findPersons(Expression $expr);
}
When querying persons from the repository, you can create new expressions with
the Expr factory class:
$expr = Expr::method('getFirstName', Expr::startsWith('Tho'))
->andMethod('getAge', Expr::greaterThan(35));
$persons = $repository->findPersons($expr);
The repository implementation can use the evaluate() method to match
individual persons against the criteria:
class PersonRepositoryImpl implements PersonRepository
{
private $persons = [];
public function findPersons(Expression $expr)
{
return Expr::filter($this->persons, $expr);
}
}
Visitors can be built to convert expressions into
other types of specifications, such as Doctrine query builders.
Domain Expressions
Extend existing expressions to build domain-specific expressions:
class IsPremium extends Method
{
public function __construct()
{
parent::__construct('isPremium', [], Expr::same(true));
}
}
class HasPreviousBookings extends Method
{
public function __construct()
{
parent::__construct(
'getBookings',
[],
Expr::count(Expr::greaterThan(0))
);
}
}
// Check if a customer is premium
if ((new IsPremium())->evaluate($customer)) {
// ...
}
// Get premium customers with bookings
$customers = $repo->findCustomers(Expr::andX([
new IsPremium(),
new HasPreviousBookings(),
]));
The following sections describe the core expressions in detail.
Expressions
The Expr class is able to create the following expressions:
Method, Description
---------------------------, --------------------------------------------------------
null(), Check that a value is null
notNull(), Check that a value is not null
isEmpty(), Check that a value is empty (using empty())
notEmpty(), Check that a value is not empty (using empty())
isInstanceOf($className), Check that a value is instance of a class (using instanceof)
equals($value), Check that a value equals another value (using ==)
notEquals($value), Check that a value does not equal another value (using !=)
same($value), Check that a value is identical to another value (using ===)
notSame($value), Check that a value does not equal another value (using !==)
greaterThan($value), Check that a value is greater than another value
greaterThanEqual($value), Check that a value is greater than or equal to another value
lessThan($value), Check that a value is less than another value
lessThanEqual($value), Check that a value is less than or equal to another value
startsWith($prefix), Check that a value starts with a given string
endsWith($suffix), Check that a value ends with a given string
contains($string), Check that a value contains a given string
matches($regExp), Check that a value matches a regular expression
in($values), Check that a value occurs in a list of values
keyExists($key), Check that a key exists in a value
keyNotExists($key), Check that a key does not exist in a value
true(), Always true (tautology)
false(), Always false (contradiction)
Selectors
With composite values like arrays or objects, you often want to match only a
part of that value (like an array key or the result of a getter) against an
expression. You can select the evaluated parts with a selector.
When you evaluate arrays, use the key() selector to match the value of an
array key:
$expr = Expr::key('age', Expr::greaterThan(10));
$expr->evaluate(['age' => 12]);
// => true
Each selector method accepts the expression as last argument that should be
evaluated for the selected value.
When evaluating objects, use property() and method() to evaluate the values
of properties and the results of method calls:
$expr = Expr::property('age', Expr::greaterThan(10));
$expr->evaluate(new Person(12));
// => true
$expr = Expr::method('getAge', Expr::greaterThan(10));
$expr->evaluate(new Person(12));
// => true
The method() selector also accepts arguments that will be passed to the
method. Pass the arguments before the evaluated expression:
$expr = Expr::method('getParameter', 'age', Expr::greaterThan(10));
$expr->evaluate(new Person(12));
// => true
You can nest selectors to evaluate expressions for nested objects or arrays:
$expr = Expr::method('getBirthDate', Expr::method('format', 'Y', Expr::lessThan(2000)));
$expr->evaluate(new Person(12));
// => false
The following table lists all available selectors:
Method, Description
------------------------, -------------------------------------------------------------------------------
key($key, $expr), Evaluate an expression for a key of an array
method($name, $expr), Evaluate an expression for the result of a method call
property($name, $expr), Evaluate an expression for the value of a property
count($expr), Evaluate an expression for the count of a collection
The count() selector accepts arrays and Countable objects.
Quantors
Quantors are applied to collections and test whether an expression matches for a
certain number of elements. A famous one is the all-quantor:
$expr = Expr::all(Expr::method('getAge', Expr::greaterThan(10)));
$expr->evaluate([new Person(12), new Person(11)]);
// => true
Quantors accept both arrays and Traversable instances. The following table
lists all available quantors:
Method, Description
------------------------, -------------------------------------------------------------------------------
all($expr), Check that an expression matches for all entries of a collection
atLeast($count, $expr), Check that an expression matches for at least $count entries of a collection
atMost($count, $expr), Check that an expression matches for at most $count entries of a collection
exactly($count, $expr), Check that an expression matches for exactly $count entries of a collection
Logical Operators
You can negate an expression with not():
$expr = Expr::not(Expr::method('getFirstName', Expr::startsWith('Tho')));
You can connect multiple expressions with "and" using the and*() methods:
$expr = Expr::method('getFirstName', Expr::startsWith('Tho'))
->andMethod('getAge', Expr::greaterThan(35));
The same is possible for the "or" operator:
$expr = Expr::method('getFirstName', Expr::startsWith('Tho'))
->orMethod('getAge', Expr::greaterThan(35));
You can use and/or inside selectors:
$expr = Expr::method('getAge', Expr::greaterThan(35)->orLessThan(20));
If you want to mix and match "and" and "or" operators, use andX() and orX()
to add embedded expressions:
$expr = Expr::method('getFirstName', Expr::startsWith('Tho'))
->andX(
Expr::method('getAge', Expr::lessThan(14))
->orMethod('isReduced', Expr::same(true))
);
Testing
To make sure that PHPUnit compares Expression objects correctly, you should
register the ExpressionComparator with PHPUnit in your PHPUnit bootstrap file:
// tests/bootstrap.php
use SebastianBergmann\Comparator\Factory;
use Webmozart\Expression\PhpUnit\ExpressionComparator;
require_once __DIR__.'/../vendor/autoload.php';
Factory::getInstance()->register(new ExpressionComparator());
Make sure the file is registered correctly in phpunit.xml.dist:
<!-- phpunit.xml.dist -->
<?xml version="1.0" encoding="UTF-8"?>
<phpunit bootstrap="tests/bootstrap.php" colors="true">
<!-- ... -->
</phpunit>
The ExpressionComparator makes sure that PHPUnit compares different
Expression instances by logical equivalence instead of by object equality.
For example, the following Expression are logically equivalent, but not equal
as objects:
// Logically equivalent
$c1 = Expr::notNull()->andSame(35);
$c2 = Expr::same(35)->andNotNull();
$c1 == $c2;
// => false
$c1->equivalentTo($c2);
// => true
// Also logically equivalent
$c1 = Expr::same(35);
$c2 = Expr::oneOf([35]);
$c1 == $c2;
// => false
$c1->equivalentTo($c2);
// => true
Expression Transformation
In some cases, you will want to transform expressions to some other
representation. A prime example is the transformation of an expression to a
Doctrine query.
You can implement a custom ExpressionVisitor to do the transformation. The
visitor's methods enterExpression() and leaveExpression() are called for
every node of the expression tree:
use Webmozart\Expression\Traversal\ExpressionVisitor;
class QueryBuilderVisitor implements ExpressionVisitor
{
private $qb;
public function __construct(QueryBuilder $qb)
{
$this->qb = $qb;
}
public function enterExpression(Expression $expr)
{
// configure the $qb...
}
public function leaveExpression(Expression $expr)
{
// configure the $qb...
}
}
Use an ExpressionTraverser to traverse an expression with your visitor:
public function expressionToQueryBuilder(Expression $expr)
{
$qb = new QueryBuilder();
$traverser = new ExpressionTraverser();
$traverser->addVisitor(new QueryBuilderVisitor($qb));
$traverser->traverse($expr);
return $qb;
}
Authors
Contribute
Contributions to the package are always welcome!
- Report any bugs or issues you find on the issue tracker.
- You can grab the source code at the package's Git repository.
Support
If you are having problems, send a mail to bschussek@gmail.com or shout out to
@webmozart on Twitter.
License
All contents of this package are licensed under the MIT license.