Use @validator in pydantic model for date comparison

Question

I'm using Pydantic and i'm trying to compare than date_from is inferior to date_to (both of these fields are optional) in my Pydantic BaseModel and return a 422 error if it's not the case.

I tried to use to method presented in the StackOverflow question: pydantic Multi-field comparison - but I didn't get any success with it, I alway got a 200 succeed.

Here's my model:

class MyModel(BaseModel):
    startFrom: Optional[date] = Field(
        ...,
        description='XXX',
        example='2023-03-15',
    )

    StartTo: Optional[date] = Field(
        ...,
        description='XXX',
        example='2023-03-31',
    )

    otherData: str = Field(
        ...,
        description='XXX',
        example='XX',
    )

    @validator('startFrom')
    def date_order(cls, startFrom, values, **kwargs):
        if ('StartTo' not in values):
            return startFrom

        if (startFrom > values['StartTo']):
            raise ValueError('startFrom must be inferior to StartTo.')
        return startFrom

I don't really know what I do wrong.

Thanks to everyone for you help :)

Please have a look at [this answer](https://stackoverflow.com/a/71258131/17865804) and [this answer](https://stackoverflow.com/a/72003724/17865804) — Chris, Mar 06 '23 at 06:57

score 2 · Accepted Answer · answered Mar 05 '23 at 20:22

2

You need to change the order of fields so startFrom comes after startTo, review the docs on order of fields.

answered Mar 05 '23 at 20:22

SColvin

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Or you can use a `root_validator`, which will get all the field values instead of depending on the order of the fields in the class. – MatsLindh Mar 05 '23 at 22:53
but the error will no have the location `startFrom` or `startTo` – SColvin Mar 06 '23 at 19:41

Use @validator in pydantic model for date comparison

1 Answers1