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Improve error messages when json schema validation fails (Pydantic discriminators)

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
backend

Research direction

Start with declarative_component_schema.py, especially SimpleRetriever.selector and the requester union shown in the issue. Inspect the related union models and their discriminator fields, then validate representative manifests to confirm failures identify missing or unexpected fields instead of producing large anyOf errors.

Written by the indexing model from the issue text.

Description

We get really noising and difficult to parse error messages when manifests don't successfully validate against the json schema.

JSON Schema (and Pydantic) have a feature called "discriminator" which can help with this:

https://docs.pydantic.dev/latest/concepts/unions/#discriminated-unions

When Union validation fails, error messages can be quite verbose, as they will produce validation errors for each case in the union. This is especially noticeable when dealing with recursive models, where reasons may be generated at each level of recursion. Discriminated unions help to simplify error messages in this case, as validation errors are only produced for the case with a matching discriminator value.

Today: we get a huge error of the input not matching one of n "anyOf" conditions, which could be tens or hundreds of lines of error, without explicitly naming the field that was extra or missing.

Afterwards: we would get an error like field 'foo' is missing or unexpected field 'food' field

Sample code from the docs:

class Model(BaseModel):
    pet: Cat | Dog | Lizard = Field(discriminator='pet_type')
    n: int

Taking our SimpleRetriever.selector field, for example:

class SimpleRetriever(BaseModel):
    ...
    requester: Union[CustomRequester, HttpRequester] = Field(
        ...,
        description="Requester component that describes how to prepare HTTP requests to send to the source API.",
    )

We'd update as follows to declare discriminator:

class SimpleRetriever(BaseModel):
    ...
    requester: Union[CustomRequester, HttpRequester] = Field(
        ...,
        description="Requester component that describes how to prepare HTTP requests to send to the source API.",
        discriminator="type",
    )
Dominant language
Python
Stars
27
Forks
56
Avg merge
3d 18h
Merged PRs (30d)
30

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