load_entity: an empty result is not a list, and resolve() pairs IRIs with the wrong entities #198

Two defects in how the result of OSW.load_entity is shaped and consumed. Both produce wrong results.

1. An empty result is an OswBaseModel, not a list

LoadEntityResult.entities is typed Union[model.OswBaseModel, List[model.OswBaseModel]]:

pydantic v1 tries the first member of the Union first. BaseModel.validate([]) succeeds, because it falls back to dict([]), which is {}. So when no page yields an entity, the result is an empty model:

>>> r = OSW.LoadEntityResult(entities=[])
>>> r.entities
OswBaseModel()
>>> bool(r.entities)
True
>>> r.entities[0]
TypeError: 'OswBaseModel' object is not subscriptable
>>> len(r.entities)
TypeError: object of type 'OswBaseModel' has no len()

A non-empty list is not affected. dict() needs each element to yield exactly two items, and an entity yields one item per field (19 for a plain Item), so validation falls through to List[...]. Checked with lists of one and two entities.

Affected caller: export_entity_jsonld wraps a non-list result in a list, so its if not entities check never fires:

For a title that yields no entity, it therefore passes [OswBaseModel()] to export_jsonld instead of raising NotFound. This part follows from the code; I did not run it end to end.

Suggested fix: type the field as List[model.OswBaseModel], or at least put List[...] first in the Union. load_entity always passes a list.

2. resolve() pairs IRIs with the wrong entities

The oold backend's resolve() pairs request.iris with load_entity(...).entities by position:

load_entity skips a page it cannot build, both when a schema is missing and when construction fails:

The list is then shorter than the titles, and every later IRI is paired with the entity of the following page. Reproduced offline, with a page that has no jsondata followed by a valid page:

titles:               ['Item:OSWAlignBad', 'Item:OSWAlignGood']
entities:             ['good']
zip as in resolve():  {'Item:OSWAlignBad': 'good'}

A reference to the first IRI resolves to the second entity, and the second IRI resolves to nothing.

Suggested fix: key the result by page title instead of by position. load_entity already sets entity.meta.wiki_page.namespace and .title on every entity it returns.

Related

#166 changes how load_entity chooses a class, and does not change either behaviour above.