Pydantic v2: pydantic_core.ValidationError: 1 validation error for Model

pydantic_core._pydantic_core.ValidationError: 1 validation error for UserModel age Input should be a valid integer, unable to parse string as an integer [type=int_parsing, input_value="twenty"]

Immediate Remediation

python

from pydantic import BaseModel, Field, field_validator

class UserModel(BaseModel):
    name: str
    age: int = Field(..., ge=0)

    # In Pydantic v2, use @field_validator instead of @validator:
    @field_validator('age', mode='before')
    @classmethod
    def parse_age(cls, v):
        if isinstance(v, str) and v.isdigit():
            return int(v)
        return v

Root Cause Analysis

Input payload failed strict schema type parsing. In Pydantic v2, type coercion rules are stricter, and legacy v1 @validator decorators are deprecated in favor of @field_validator.

Verification & Guardrails

In Pydantic v2, use model_dump() and model_validate() instead of dict() and parse_obj().
Use model_config = ConfigDict(coerce_numbers_to_str=True) for flexible string inputs.

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