implement-cqrs-handlers

implement-cqrs-handlers

Handlers live in src/Adapter/{Domain}/CommandHandler/ and QueryHandler/. See CQRS/CONTEXT.md for conventions (#[AsCommandHandler]/#[AsQueryHandler] attributes, no cross-handler calls, return types).

1. Add handler

Add{Domain}Handler.php implementing Add{Domain}HandlerInterface:

• Inject {Domain}Repository
• handle(Add{Domain}Command $command): {Domain}Id:
  • Construct the ObjectModel entity from command data
  • For multilingual fields, map $command->getLocalizedNames() to the lang array
  • Call $this->repository->create(...)
  • Return the new {Domain}Id
• Catch persistence exceptions, rethrow as domain exceptions

Reference: src/Adapter/Tax/CommandHandler/AddTaxHandler.php (simple), src/Adapter/Manufacturer/CommandHandler/AddManufacturerHandler.php (with image)

2. Edit handler (partial-update)

Edit{Domain}Handler.php implementing Edit{Domain}HandlerInterface:

• Load entity: $entity = $this->repository->get{Domain}($command->getId())
• For each field: if ($command->getName() !== null) { $entity->name = $command->getName(); }
• Apply only non-null fields — never overwrite with null
• Call $this->repository->update($entity)
• Sub-resource commands are dispatched independently, not composed here

Reference: src/Adapter/Tax/CommandHandler/EditTaxHandler.php (simple), src/Adapter/Carrier/CommandHandler/EditCarrierHandler.php (many fields)

3. Delete handler

Delete{Domain}Handler.php implementing Delete{Domain}HandlerInterface:

• Load entity to verify existence (throws {Domain}NotFoundException)
• Check business constraints: if entity is referenced by active orders/other entities, throw CannotDelete{Domain}Exception
• Call $this->repository->delete($command->getId())

4. Toggle status handler

Toggle{Domain}StatusHandler.php:

• Load entity by ID
• Flip: $entity->active = !$entity->active
• Call repository update
• Return void — the controller reads back state from the grid

5. Sub-resource handler (if sub-resources exist)

Set{Domain}{SubResource}sHandler.php:

Two strategies depending on complexity:

Strategy A: Atomic replace (simpler, quicker)

Used when sub-resources have no identity of their own or when maintaining existing rows isn't important:

• Begin a DB transaction
• Delete all existing sub-resource rows for the entity
• Insert new rows from $command->getItems()
• Commit; on failure, rollback and throw domain exception
• Empty array = delete all (valid use case)

Reference: src/Adapter/Carrier/CommandHandler/SetCarrierRangesHandler.php

Strategy B: Incremental update (cleaner, preserves existing sub-resources)

Preferred when sub-resources have their own identity or when preserving existing rows matters (e.g., to keep audit trails, auto-increment IDs, or related data):

• Load existing sub-resources for the entity
• Compare with the new collection: identify additions, updates, and removals
• Apply only the necessary changes (insert new, update changed, delete removed)
• Wrap in a transaction

Choose Strategy B when possible for cleaner data management. Use Strategy A when sub-resources are simple value-like collections without individual identity.

6. Get-for-editing handler

Get{Domain}ForEditingHandler.php in QueryHandler/:

• Load entity via repository
• Map ALL fields to the return DTO: scalars, multilingual (array keyed by langId), related IDs
• Return typed Editable{Domain} DTO (with scalar types only — no VOs in the DTO)
• No write side effects

Reference: src/Adapter/Tax/QueryHandler/GetTaxForEditingHandler.php (simple)

7. List query handler (if explicit query exists)

Most domains use the grid QueryBuilder pattern — no handler needed. Only create if the domain uses an explicit Get{Domain}sForListing query class.

Rules

Conventions (attributes, no SQL, no cross-handler calls, return types) are in CQRS/CONTEXT.md. Skill-specific reminders:

• Check null before every field update in Edit handler (partial-update pattern)
• Always verify existence before deletion — never delete blindly