References/Meta Artifact

referenceplatformCARE 3.0+

A MetaArtifact attaches a freeform metadata payload to any Care object without a dedicated foreign key. You reach for it when a feature needs to hang structured data — a drawing on a patient, say — off an existing record without adding a column or a join table.

Storage and schema split across two layers. The Django model stays loose: object_value is an opaque JSONField, and associating_type / object_type are bare CharFields. The Pydantic resource specs constrain those values to known enums and define the request/response shapes the API accepts.

Source:

Model: [https://github.com/ohcnetwork/care/blob/develop/care/emr/models/meta_artifact.py care/emr/models/meta_artifact.py]
Resource specs: [https://github.com/ohcnetwork/care/blob/develop/care/emr/resources/meta_artifact/spec.py care/emr/resources/meta_artifact/spec.py]

Models

Model	Purpose
`MetaArtifact`	Generic, polymorphic metadata record attached to any Care object by type + external ID

MetaArtifact extends EMRBaseModel, the shared Care EMR base that provides external_id, the audit fields created_by / updated_by and created_date / modified_date, and the soft-delete flag deleted.

`MetaArtifact` fields

Association

There is no Django ForeignKey to a parent. A MetaArtifact points at its target by storing the target's type and external_id instead.

Field	Type	Notes {{Field\|model=MetaArtifact\|section=Association\|name=associating_type\|type=CharField(255)\|notes=Non-null. The kind of object this artifact hangs off. API-constrained to [[#metaartifactassociatingtypechoices-values}} {{Field\|model=MetaArtifact\|section=Association\|name=associating_external_id\|type=UUIDField\|notes=Non-null. The parent's `external_id`. Set server-side from the spec's `associating_id` (see [[#resource-specs-api-schema}}

A composite database index covers these two fields (see Methods & save behaviour), so looking up every artifact for a given parent stays cheap.

Content

Field	Type	Notes
`name`	`CharField(255)`	Spec rejects blank/whitespace-only on create {{Field\|model=MetaArtifact\|section=Content\|name=object_type\|type=CharField(255)\|notes=Names the shape held in `object_value`. API-constrained to [[#metaartifactobjecttypechoices-values}}
`object_value`	`JSONField`	The payload. Spec types it as `dict`
`note`	`TextField`	Nullable. Spec: `str`

Enum values

Two str enums constrain associating_type and object_type at the API layer. Both live in spec.py — this resource has no separate constants.py or valueset.py.

`MetaArtifactAssociatingTypeChoices` values

Binds associating_type.

Value
`patient`
`encounter`

`MetaArtifactObjectTypeChoices` values

Binds object_type.

Value
`drawing`

Resource specs (API schema)

All specs extend EMRResource ([https://github.com/ohcnetwork/care/blob/develop/care/emr/resources/base.py care/emr/resources/base.py]), which provides serialize (model → pydantic) and de_serialize (pydantic → model) along with the perform_extra_serialization / perform_extra_deserialization hooks. __model__ = MetaArtifact.

Spec	Role	Fields exposed
`MetaArtifactBaseSpec`	shared	None), `object_value` (`dict \| list`), `note` (`str \| None`)
`MetaArtifactCreateSpec`	write · create	base + `associating_type`, `associating_id` (`UUID4`), `object_type`, `name`
`MetaArtifactUpdateSpec`	write · update	identical to `MetaArtifactBaseSpec` (only `object_value` / `note` are mutable; association and type are fixed after create)
`MetaArtifactReadSpec`	read · detail/list	None), `updated_by` (`dict \| None`)

Field-level details and validation:

Field	Spec type	Required	Default	Validation / behaviour
`id`	None	optional	`None`	Read-only; populated from `obj.external_id` in `perform_extra_serialization`
`object_value`	list	yes	—	Arbitrary JSON object or array
`note`	None	no	`None`	Free text
`associating_type`	`MetaArtifactAssociatingTypeChoices`	yes (create)	—	`patient` or `encounter`
`associating_id`	`UUID4`	yes (create)	—	Parent's `external_id`; copied to model field `associating_external_id` in `perform_extra_deserialization`
`object_type`	`MetaArtifactObjectTypeChoices`	yes (create)	—	`drawing`
`name`	`str`	yes (create)	—	`validate_name` rejects blank/whitespace-only with `"Name cannot be empty"`
`created_date`	`datetime`	read	—	From `EMRBaseModel`
`modified_date`	`datetime`	read	—	From `EMRBaseModel`
`created_by` / `updated_by`	None	read	`None`	Serialized via `serialize_audit_users` (cached `UserSpec`)

Server-maintained behaviour:

Create (MetaArtifactCreateSpec.perform_extra_deserialization): sets obj.associating_external_id = self.associating_id. Clients send the parent's external_id as associating_id; the model stores it under associating_external_id.
Read (MetaArtifactReadSpec.perform_extra_serialization): sets mapping["id"] = obj.external_id and calls serialize_audit_users to attach created_by / updated_by.
Update: MetaArtifactUpdateSpec exposes only object_value and note (plus the inherited optional id). It never re-accepts associating_type, associating_id, object_type, or name, so association and classification are immutable once the record exists.

No field on this resource binds to a value set (there is no valueset.py); the only constrained vocabularies are the two str enums above.

Methods & save behaviour

MetaArtifact adds no custom methods and overrides neither save() nor delete(). Audit and soft-delete behaviour come entirely from EMRBaseModel.

Its Meta declares one composite index to back parent-object lookups:

Index(fields=["associating_type", "associating_external_id"])

API integration notes

Reference the target by its external_id (UUID), never its internal primary key, and pass it as associating_id on create. The associating_type + associating_external_id pair lets one table hold metadata for many Care object types without per-type foreign keys.
Add a new association or artifact kind by extending the str enums in spec.py — no schema migration, since the underlying CharFields are already open.
object_value accepts any dict | list, so payloads carry feature-specific structure without migrations; object_type records which shape to expect (e.g. drawing).
After creation, associating_type, associating_id, object_type, and name are fixed. Only object_value and note can change, via MetaArtifactUpdateSpec.
EMRBaseModel maintains the audit fields (created_by, updated_by, created_date, modified_date), the public external_id (exposed as id), and soft-delete (deleted). Don't set them from clients.

Reference: References/Encounter