Builder Pattern Generator

Creates Builder pattern infrastructure for step-by-step construction of complex objects.

When to Use

Scenario	Example
Many constructor parameters	Order with 10+ fields
Optional parameters	Email with optional CC, BCC
Complex validation	Build-time validation
Step-by-step construction	Query building
Multiple representations	Different order types

Component Characteristics

Builder Interface

• Defines building steps
• Returns self for fluent interface
• Has build() method for final product

Concrete Builder

• Implements building steps
• Maintains product state
• Validates before building

Director (Optional)

• Defines construction order
• Reusable build sequences
• Hides complexity from client

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Generation Process

Step 1: Analyze Requirements

Determine:

• Target product class
• Required vs optional properties
• Validation rules
• Whether Director is needed

Step 2: Generate Builder Components

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

1. {Name}BuilderInterface.php — Builder contract
2. {Name}Builder.php — Concrete builder implementation
3. BuilderValidationException.php — Validation exception
4. {Name}Director.php — Optional director for common builds

Step 3: Generate Tests

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

1. {Name}BuilderTest.php — Builder functionality tests

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File Placement

Component	Path
Builder Interface	src/Domain/{BoundedContext}/Builder/
Concrete Builder	src/Domain/{BoundedContext}/Builder/
Director	src/Domain/{BoundedContext}/Builder/
Exception	src/Domain/{BoundedContext}/Builder/
Unit Tests	tests/Unit/Domain/{BoundedContext}/Builder/

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Naming Conventions

Component	Pattern	Example
Interface	{Name}BuilderInterface	OrderBuilderInterface
Concrete Builder	{Name}Builder	OrderBuilder
Director	{Name}Director	OrderDirector
Exception	BuilderValidationException	BuilderValidationException
Test	{ClassName}Test	OrderBuilderTest

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Quick Template Reference

Builder Interface

interface {Name}BuilderInterface
{
    public function with{Property1}({Type1} $value): self;
    public function with{Property2}({Type2} $value): self;
    public function build(): {Product};
    public function reset(): self;
}

Concrete Builder

final class {Name}Builder implements {Name}BuilderInterface
{
    private ?{Type1} ${property1} = null;
    private ?{Type2} ${property2} = null;
    private array $errors = [];

    public function with{Property1}({Type1} $value): self
    {
        $this->{property1} = $value;
        return $this;
    }

    public function build(): {Product}
    {
        $this->validate();
        if ($this->errors !== []) {
            throw new BuilderValidationException($this->errors);
        }
        return new {Product}(...);
    }

    public function reset(): self
    {
        $this->{property1} = null;
        $this->errors = [];
        return $this;
    }
}

Director

final readonly class {Name}Director
{
    public function __construct(private {Name}BuilderInterface $builder) {}

    public function buildMinimal{Name}(/* required params */): {Product}
    {
        return $this->builder
            ->reset()
            ->with{Required1}($value1)
            ->build();
    }

    public function buildFull{Name}(/* all params */): {Product}
    {
        return $this->builder
            ->reset()
            ->with{Property1}($value1)
            ->with{Property2}($value2)
            ->build();
    }
}

---

Usage Example

// Direct builder usage
$order = (new OrderBuilder())
    ->forCustomer($customerId)
    ->withShippingAddress($address)
    ->addItem($item1)
    ->addItem($item2)
    ->withDiscountCode('SAVE10')
    ->build();

// Using Director
$director = new OrderDirector(new OrderBuilder());
$minimalOrder = $director->buildMinimalOrder($customerId, $address, $item);
$giftOrder = $director->buildGiftOrder($customerId, $shipping, $billing, $items, 'Happy Birthday!');

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Anti-patterns to Avoid

Anti-pattern	Problem	Solution
No Validation	Invalid objects built	Validate in build()
Mutable Product	Product can change after build	Return immutable objects
Missing Reset	Builder state persists	Add reset() method
Too Many Steps	Hard to use	Use Director or defaults
No Fluent Interface	Verbose client code	Return self from setters

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References

For complete PHP templates and examples, see:

• references/templates.md — Builder, QueryBuilder templates
• references/examples.md — OrderBuilder, EmailBuilder examples and tests