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Application Basics
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Validation
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Async & Integration
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FastAPI / Validation

model validator

Learn model validator in FastAPI with a dedicated explanation, a topic-specific example, edge guidance, and a mastery check.

12 min read • Beginner
fastapi-016.py
python 
from pydantic import model_validator
class Period(BaseModel):
    start:date; end:date
    @model_validator(mode="after")
    def order(self):
        if self.end < self.start: raise ValueError("end before start")
        return self
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