CollectionViewSet

CollectionViewSet is a ready-made ImplMixin implementation that stores data in any Python in-memory collection. It is ideal for prototyping, demos, and tests — no database required.

Supported container types

Container type	Supported operations
list / MutableSequence	list, retrieve, create, update, destroy
set / MutableSet	list, retrieve, create, update, destroy
dict / MutableMapping	list, retrieve, create, update, destroy
Any Iterable (read-only)	list, retrieve only

Basic usage

from pydantic import BaseModel
from fastapi_viewsets.collection_viewset import CollectionViewSet
from fastapi_viewsets.mixins import BulkViewSetMixin
from fastapi_viewsets.decorators.route_viewset import route_viewset
from fastapi import APIRouter

class Item(BaseModel):
    id: int | None = None
    name: str
    price: float

items: list[Item] = []
router = APIRouter()

@route_viewset(router, base_path="/items", pk_field_name="id")
class ItemViewSet(CollectionViewSet[int, Item], BulkViewSetMixin[int, Item]):
    def __init__(self):
        super().__init__(container=items, pk_field="id")

That's it — all CRUD and bulk endpoints are available with no further code.

Constructor parameters

CollectionViewSet(container, pk_field="id")

Parameter	Type	Default	Description
container	collection	—	The backing Python collection
pk_field	str	"id"	Name of the primary key attribute/key on each item

Auto-increment PK

If your Pydantic model has a field annotated with json_schema_extra={"autoinc_int": True}, CollectionViewSet will automatically assign the next integer value when creating a new record and the field is None or 0.

class Item(BaseModel):
    id: int | None = Field(default=None, json_schema_extra={"autoinc_int": True})
    name: str
    price: float

Using a dict container

When using a dict, the key is the PK and the value is the item. CollectionViewSet handles the mapping transparently:

items: dict[int, Item] = {}

@route_viewset(router, base_path="/items", pk_field_name="id")
class ItemViewSet(CollectionViewSet[int, Item], BulkViewSetMixin[int, Item]):
    def __init__(self):
        super().__init__(container=items, pk_field="id")

Extending with custom logic

You can override any container_* method to add custom behaviour (e.g. validation, side effects):

class ItemViewSet(CollectionViewSet[int, Item], BulkViewSetMixin[int, Item]):
    def __init__(self):
        super().__init__(container=items, pk_field="id")

    async def container_add(self, data: Item) -> Item:
        # custom pre-processing
        data.name = data.name.strip()
        return await super().container_add(data)