{
  "id": "python/fastapi-pydantic-v2-validator-removed",
  "signature": "PydanticUserError: `@validator` cannot be applied to instance methods. Use `@field_validator` instead.",
  "signature_zh": "PydanticUserError: `@validator` 不能应用于实例方法，请改用 `@field_validator`。",
  "regex": "PydanticUserError:\\ `@validator`\\ cannot\\ be\\ applied\\ to\\ instance\\ methods\\.\\ Use\\ `@field_validator`\\ instead\\.",
  "domain": "python",
  "category": "runtime_error",
  "subcategory": null,
  "root_cause": "Code written for Pydantic v1 uses the removed `validator` decorator under Pydantic v2.",
  "root_cause_type": "generic",
  "root_cause_zh": "为 Pydantic v1 编写的代码在 Pydantic v2 下使用了已移除的 `validator` 装饰器。",
  "versions": [
    {
      "version": "3.x",
      "introduced": null,
      "deprecated": null,
      "removed": null,
      "behavior_change": null,
      "status": "active"
    }
  ],
  "os_specific": {},
  "dead_ends": [
    {
      "action": "",
      "why_fails": "FastAPI 0.100+ expects v2; downgrading causes other incompatibilities.",
      "fail_rate": 0.6,
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "why_fails": "Loses validation logic and may accept bad data.",
      "fail_rate": 0.7,
      "condition": "",
      "sources": []
    }
  ],
  "workarounds": [
    {
      "action": "",
      "success_rate": 0.92,
      "how": "Migrate to field_validator:\nfrom pydantic import field_validator\n@field_validator('name')\n@classmethod\ndef check(cls, v): ...",
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "success_rate": 0.85,
      "how": "Use bump-pydantic to automate migration.",
      "condition": "",
      "sources": []
    }
  ],
  "workarounds_zh": [],
  "transition_graph": {
    "leads_to": [],
    "preceded_by": [],
    "frequently_confused_with": []
  },
  "official_doc_url": null,
  "official_doc_section": null,
  "error_code": null,
  "verification_tier": "ai_generated",
  "confidence": 0.88,
  "fix_success_rate": 0.8,
  "resolvable": "true",
  "first_seen": "2024-04-18",
  "last_confirmed": "2025-01-01",
  "last_updated": "2025-01-01",
  "evidence_count": 0,
  "tags": [],
  "locale": "en",
  "aliases": []
}