DTO Contracts

DTOs define structured, transport-safe data contracts used between layers of the application.

They exist to replace unstructured arrays when data shape matters, is reused, or must remain consistent across boundaries.

1. Responsibility

DTOs MUST:

• represent structured application data
• act as transport carriers between layers
• be filled by Transformers
• avoid business logic
• avoid persistence logic

DTOs MUST NOT:

• contain ORM logic
• contain validation rules
• contain side effects
• depend on framework components (Request, Eloquent models, etc.)

2. Structure

DTOs are simple POPOs with fluent getters and setters.

Example:

class InvoiceDto
{
    private int $invoiceId;
    private int $companyId;
    private float $amount;

    public function getInvoiceId(): int
    {
        return $this->invoiceId;
    }

    public function setInvoiceId(int $invoiceId): self
    {
        $this->invoiceId = $invoiceId;
        return $this;
    }

    public function getCompanyId(): int
    {
        return $this->companyId;
    }

    public function setCompanyId(int $companyId): self
    {
        $this->companyId = $companyId;
        return $this;
    }

    public function getAmount(): float
    {
        return $this->amount;
    }

    public function setAmount(float $amount): self
    {
        $this->amount = $amount;
        return $this;
    }
}

3. Creation Rule

DTOs MUST be created via Transformers.

$dto = InvoiceTransformer::fromModel($invoice);

or

$dto = InvoiceTransformer::fromArray($data);

DTOs MUST NOT be manually assembled inside services unless trivial and explicitly justified.

4. Transformer Dependency Rule

Transformers are the ONLY layer allowed to construct DTOs.

DTOs MUST NOT depend on Transformers.

Direction is strictly:

Model / Array → Transformer → DTO → Service

5. When DTOs are Required

Use DTOs when:

• data is shared across multiple services
• structure must remain stable across changes
• transformation logic exists (model → structured output)
• array shape would otherwise be ambiguous or inconsistent

6. When DTOs are NOT Required

DTOs MAY be skipped when:

• data is short-lived within a single method
• input comes from a validated FormRequest
• structure is trivial and not reused elsewhere

7. Core Principle

DTOs are explicit data contracts, not business logic containers.

IDE Hints (Optional)

DTOs MAY include region markers to improve IDE navigation (e.g. PhpStorm folding).

These are purely cosmetic and MUST NOT affect runtime behavior or architecture decisions.

Example:

class InvoiceDto
{
    #region Properties
    private int $invoiceId;
    private int $companyId;
    private float $amount;
    #endregion

    #region Getters
    public function getInvoiceId(): int { ... }
    public function getCompanyId(): int { ... }
    public function getAmount(): float { ... }
    #endregion

    #region Setters
    public function setInvoiceId(int $invoiceId): self { ... }
    public function setCompanyId(int $companyId): self { ... }
    public function setAmount(float $amount): self { ... }
    #endregion
}

They exist to stabilize data shape across the system, not to introduce unnecessary abstraction.