Specification Generator

Generate DDD-compliant Specifications for encapsulating business rules and filtering logic.

Specification Characteristics

• Single Responsibility: One business rule per specification
• Composable: AND, OR, NOT combinations
• Reusable: Same spec for validation and querying
• Domain Language: Named using ubiquitous language
• Testable: Easy to unit test in isolation
• Immutable: No state changes after creation

When to Use Specification

Scenario	Example
Business rule validation	IsActiveCustomer, CanPlaceOrder
Collection filtering	OverdueInvoice, PremiumProduct
Repository queries	OrdersByCustomer, ActiveUsers
Policy enforcement	EligibleForDiscount, CanBeShipped
Complex conditions	Composite AND/OR specifications

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Generation Process

Step 1: Generate Base Infrastructure

Path: src/Domain/Shared/Specification/

1. SpecificationInterface.php — Generic interface with isSatisfiedBy()
2. AbstractSpecification.php — Base with AND/OR/NOT methods
3. AndSpecification.php — Composite AND
4. OrSpecification.php — Composite OR
5. NotSpecification.php — Negation wrapper

Step 2: Generate Concrete Specification

Path: src/Domain/{BoundedContext}/Specification/

1. {Name}Specification.php — Implements business rule

Step 3: Generate Tests

Path: tests/Unit/Domain/{BoundedContext}/Specification/

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File Placement

Component	Path
Base Interface	src/Domain/Shared/Specification/
Abstract Spec	src/Domain/Shared/Specification/
Composites	src/Domain/Shared/Specification/
Concrete Specs	src/Domain/{BoundedContext}/Specification/
Unit Tests	tests/Unit/Domain/{BoundedContext}/Specification/

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Naming Conventions

Pattern	Example
Is{Condition}Specification	IsActiveCustomerSpecification
Has{Property}Specification	HasPurchaseHistorySpecification
Can{Action}Specification	CanBeCancelledSpecification
Factory Method	IsOverdueInvoiceSpecification::now()

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Quick Template Reference

Specification Interface

/**
 * @template T
 */
interface SpecificationInterface
{
    public function isSatisfiedBy(mixed $candidate): bool;
    public function and(self $other): self;
    public function or(self $other): self;
    public function not(): self;
}

Concrete Specification

/**
 * @extends AbstractSpecification<{Entity}>
 */
final readonly class {Name}Specification extends AbstractSpecification
{
    public function __construct({parameters}) {}

    public function isSatisfiedBy(mixed $candidate): bool
    {
        if (!$candidate instanceof {Entity}) {
            return false;
        }
        return {businessRule};
    }
}

Composite Usage

$eligible = $isActive
    ->and($hasPurchases)
    ->and($isNotBlacklisted->not());

$customers = array_filter(
    $all,
    fn($c) => $eligible->isSatisfiedBy($c)
);

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Anti-patterns to Avoid

Anti-pattern	Problem	Solution
God Specification	Too many conditions	Split into composable specs
Side Effects	Modifies candidate	Keep pure, read-only
Infrastructure	DB calls in spec	Keep in domain, use for in-memory
Weak Typing	isSatisfiedBy(mixed)	Add type check first
No Composition	Copy-paste conditions	Use AND/OR composition

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References

For complete PHP templates and examples, see:

• references/templates.md — Interface, Abstract, Composite, Concrete templates
• references/examples.md — Customer, Product, Invoice, Order specifications and tests