Data Transformation Tracer

Overview

Traces how data transforms as it passes through application layers — from raw HTTP input through DTOs, Commands, Entities, and back to Response objects. Identifies mappers, serializers, converters, and potential data loss points.

Transformation Chain Patterns

Standard CQRS Chain

HTTP Request Body (JSON/Form)
  → Request DTO (validated input)
    → Command/Query (application layer input)
      → Entity/Aggregate (domain model)
        → Domain Event (side effect data)
        → Response DTO (output format)
          → HTTP Response (JSON/XML)

Detection Patterns

Input Transformation

# Request DTOs / Form Requests
Grep: "class.*Request|class.*Input" --glob "**/Api/**/*.php"
Grep: "class.*Request" --glob "**/Presentation/**/*.php"

# Request to Command mapping
Grep: "new.*Command\\(|Command::from|Command::create" --glob "**/*.php"

# Deserialization
Grep: "deserialize|fromArray|fromRequest|fromJson" --glob "**/*.php"
Grep: "Serializer::deserialize|denormalize" --glob "**/*.php"

Entity Transformation

# Entity factories / named constructors
Grep: "static function (create|from|of|new)" --glob "**/Domain/**/*.php"

# Entity to DTO conversion
Grep: "function (toArray|toDTO|toResponse|toView)" --glob "**/Domain/**/*.php"
Grep: "::fromEntity|::fromDomain|::fromModel" --glob "**/*.php"

Output Transformation

# Response DTOs
Grep: "class.*Response|class.*Output|class.*View" --glob "**/Api/**/*.php"
Grep: "class.*Resource" --glob "**/Http/**/*.php"

# Serialization
Grep: "jsonSerialize|toArray|normalize" --glob "**/*.php"
Grep: "JsonResponse|json_encode" --glob "**/*.php"

# Collection transformation
Grep: "->map\\(|array_map|->transform" --glob "**/*.php"

Mappers and Converters

# Explicit mapper classes
Grep: "class.*Mapper|class.*Converter|class.*Transformer|class.*Assembler" --glob "**/*.php"

# Mapping methods
Grep: "function (map|convert|transform|assemble|adapt)" --glob "**/*.php"

# AutoMapper / Symfony Serializer
Grep: "AutoMapper|ObjectNormalizer|PropertyNormalizer" --glob "**/*.php"

Analysis Process

Step 1: Identify Transformation Points

For a given request flow:

1. Read the entry point — what data format comes in
2. Find each class boundary — where data changes shape
3. Read constructor/factory — what fields are mapped
4. Track field names — which fields are renamed, combined, or dropped

Step 2: Map Field Transformations

Source	Target	Transformation
request.customer_name	CreateOrderCommand.customerName	snake_case → camelCase
command.customerId	Customer entity	ID → full entity (repo lookup)
entity.createdAt	response.created_at	DateTime → string ISO 8601
entity.money	response.amount	Money VO → float

Step 3: Identify Data Loss Points

Check for:

• Fields present in source but missing in target
• Type narrowing (DateTime → string, loses timezone)
• Precision loss (float → int)
• Relationship flattening (Entity → ID only)

Output Format

## Data Transformation Map

### Flow: Create Order

#### Transformation Chain

[1] JSON Input { "customer_id": "uuid-123", "items": [{"product_id": "p-1", "quantity": 2}], "shipping_address": {"street": "...", "city": "..."} } │ ▼ (Deserialization + Validation) [2] CreateOrderRequest customerId: string (validated: uuid format) items: CreateOrderItemRequest[] (validated: non-empty) shippingAddress: AddressRequest (validated: all fields required) │ ▼ (Mapping: CreateOrderRequest → CreateOrderCommand) [3] CreateOrderCommand customerId: CustomerId (Value Object wrapping) items: OrderItemData[] (DTO with productId + quantity) shippingAddress: AddressData (DTO) │ ▼ (Domain Factory: Order::create()) [4] Order Entity id: OrderId (generated) customerId: CustomerId items: OrderItem[] (entities with calculated prices) total: Money (calculated from items) status: OrderStatus::Pending shippingAddress: ShippingAddress (Value Object) createdAt: DateTimeImmutable │ ▼ (Response Mapping: OrderResponse::fromEntity()) [5] OrderResponse id: string (OrderId → string) customerId: string (CustomerId → string) items: OrderItemResponse[] (entity → response) total: float (Money → float, currency separate) currency: string (from Money) status: string (enum → string) shippingAddress: AddressResponse createdAt: string (ISO 8601) │ ▼ (JSON Serialization) [6] JSON Output {"id": "...", "customer_id": "...", "total": 150.00, ...}

#### Field Mapping Table

| Layer | Field | Type | Source | Transformation |
|-------|-------|------|--------|---------------|
| Input → Request | customer_id → customerId | string | JSON key | snake → camel |
| Request → Command | customerId → customerId | string → CustomerId | DTO | Wrap in VO |
| Command → Entity | items → OrderItem[] | DTO[] → Entity[] | Factory | Enrich with prices |
| Entity → Response | total → total | Money → float | Mapper | Extract amount |
| Entity → Response | createdAt → createdAt | DateTimeImmutable → string | Mapper | Format ISO 8601 |
| Response → JSON | customerId → customer_id | string | Serializer | camel → snake |

#### Data Enrichment Points

| Step | What's Added | Source |
|------|-------------|--------|
| Command → Entity | OrderId | Generated (UUID) |
| Command → Entity | Item prices | ProductRepository lookup |
| Command → Entity | Total amount | Calculated from items |
| Command → Entity | Created timestamp | System clock |
| Command → Entity | Initial status | Domain default (Pending) |

#### Potential Data Loss Points

| Step | Field | Issue |
|------|-------|-------|
| Money → float | precision | Floating point precision loss |
| DateTime → string | timezone | Check if timezone preserved |
| Entity → Response | internal state | Domain internals not exposed (expected) |

Transformation Quality Indicators

Indicator	Good	Warning
Type safety	Typed DTOs at boundaries	Untyped arrays
Validation	At input boundary	Scattered or missing
Mapping	Explicit mapper/factory	Implicit in controller
Value Objects	Domain uses VOs	Primitives throughout
Serialization	Controlled (toArray/normalize)	json_encode on entity

Common Anti-Patterns

Anti-Pattern	Detection	Issue
Entity as Response	return json_encode($entity)	Exposes internals
Array transport	$data = ['key' => $value]	No type safety
Missing DTO	Controller → Repository direct	Skips validation
Leaky abstraction	Domain types in API response	Tight coupling

Integration

This skill is used by:

• data-flow-analyst — documents data transformation chains
• trace-request-lifecycle — enriches lifecycle with data details
• explain-business-process — shows data perspective of processes