docs/standards/src/lib/05_crud_template.md

CRUD Template

Summary

Every resource follows the same four-file slice. Repetition is intentional: it makes the codebase predictable and generatable.

---

The slice

domain/<resource>/
    models.py               # pure Pydantic model (no DB fields)
    ports/
        db.py               # document model + repository factory
        service.py          # service class + factory
        converters.py       # (optional) transforms

The id rule (model vs. document)

Two different objects, two different jobs:

Object	Lives in	Has id?	Purpose
Domain model	domain/<resource>/models.py	No	business shape, framework-free
Document	domain/<resource>/ports/db.py	Yes (from BaseDocument)	Mongo persistence shape

BaseDocument (mongo-ops) supplies id: Optional[PyObjectId] (aliased to _id) plus created_at / updated_at. The domain model must not declare id; Mongo owns it.

Trap — generated wire models. openapi-first models produces the HTTP contract (see the Build Recipe, step 3). Response schemas frequently declare a required id: str, so a generated class is not a domain model. If you write class ItemDocument(Item, BaseDocument) and Item re-exports a required id: str, that field shadows BaseDocument.id and no Mongo _id can ever be set. Fix it one of three ways:

1. Preferred: keep the domain model id-free (hand-author it from the CRUD template), and keep the required id only on the wire model.
2. Order the bases so the document wins: class ItemDocument(BaseDocument, Item).
3. Keep a separate document type and translate with ports/converters.py.

models.py

A framework-free Pydantic model describing the business shape (no id).

class Item(BaseModel):
    name: str
    quantity: int = 0

ports/db.py

The persistence model extends the business model and adds database concerns. The repository factory selects the right repository flavour.

# Item is id-free; BaseDocument adds id/created_at/updated_at.
class ItemDocument(Item, BaseDocument):
    pass

def create_item_repo(*, owner_repo=None) -> ItemRepository:
    return repo_factory(
        collection="items",
        document=ItemDocument,
        populate_rules=[PopulateRule(field="owner", collection="users")],
        cache=None,               # or a CachedBaseRepository config
    )

ports/service.py

The service is built through the DI library, injecting the repository. The generic CRUD base provides create/read/update/patch/delete/search/....

class ItemService(CrudsServiceAdaptor[Item, ItemDocument]):
    model = Item
    schema = ItemDocument

def get_item_service(repo) -> ItemService:
    return build(ItemService, instances={"repo": repo})

Naming conventions

Concept	Convention
collection	plural snake case (items)
document	<Resource>Document
repository factory	create_<resource>_repo
service	<Resource>Service
service factory	get_<resource>_service
resource key	<resource>_svc
operationId	list_items, create_item, ...

Optional files

• converters.py — pure functions mapping between domain types.
• ports/enrichment.py — adapts a pipeline into an async callable the service can invoke (used when a resource is populated by a pipeline).