{
  "id": "python/fastapi-pydantic-v1-v2-migration-validator",
  "signature": "PydanticUserError: `@validator` cannot be applied to instance methods",
  "signature_zh": "PydanticUserError: `@validator` 不能应用于实例方法。",
  "regex": "PydanticUserError:\\ `@validator`\\ cannot\\ be\\ applied\\ to\\ instance\\ methods",
  "domain": "python",
  "category": "type_error",
  "subcategory": null,
  "root_cause": "Code migrated to Pydantic v2 but still uses `@validator` without `@classmethod`, or uses removed v1 APIs.",
  "root_cause_type": "generic",
  "root_cause_zh": "代码迁移到 Pydantic v2 后仍使用 `@validator` 且未加 `@classmethod`，或使用了已移除的 v1 API。",
  "versions": [
    {
      "version": "2.x",
      "introduced": null,
      "deprecated": null,
      "removed": null,
      "behavior_change": null,
      "status": "active"
    }
  ],
  "os_specific": {},
  "dead_ends": [
    {
      "action": "",
      "why_fails": "Blocks FastAPI updates and other deps; temporary only.",
      "fail_rate": 0.6,
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "why_fails": "Unrelated to validator decorator usage.",
      "fail_rate": 0.9,
      "condition": "",
      "sources": []
    }
  ],
  "workarounds": [
    {
      "action": "",
      "success_rate": 0.95,
      "how": "from pydantic import field_validator\nclass M(BaseModel):\n    x: int\n    @field_validator('x')\n    @classmethod\n    def check(cls, v):\n        return v",
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "success_rate": 0.9,
      "how": "@validator('x')\n@classmethod\ndef check(cls, v): ...",
      "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": "2024-03-06",
  "last_confirmed": "2025-01-01",
  "last_updated": "2025-01-01",
  "evidence_count": 0,
  "tags": [],
  "locale": "en",
  "aliases": []
}