{
  "id": "python/fastapi-missing-form-data",
  "signature": "fastapi.exceptions.RequestValidationError: 1 validation error for Body\nbody -> username\n  field required (type=value_error.missing)",
  "signature_zh": "fastapi.exceptions.RequestValidationError: Body 有 1 个验证错误\nbody -> username\n  字段必填 (type=value_error.missing)",
  "regex": "fastapi\\.exceptions\\.RequestValidationError:\\ 1\\ validation\\ error\\ for\\ Body\\\nbody\\ \\->\\ username\\\n\\ \\ field\\ required\\ \\(type=value_error\\.missing\\)",
  "domain": "python",
  "category": "data_error",
  "subcategory": null,
  "root_cause": "Endpoint declares Form(...) but client sends JSON, or declares JSON body but client sends form-urlencoded.",
  "root_cause_type": "generic",
  "root_cause_zh": "端点声明了 Form(...) 但客户端发送 JSON，或声明了 JSON body 但客户端发送 form-urlencoded。",
  "versions": [
    {
      "version": "0.100+",
      "introduced": null,
      "deprecated": null,
      "removed": null,
      "behavior_change": null,
      "status": "active"
    },
    {
      "version": "0.110+",
      "introduced": null,
      "deprecated": null,
      "removed": null,
      "behavior_change": null,
      "status": "active"
    }
  ],
  "os_specific": {},
  "dead_ends": [
    {
      "action": "",
      "why_fails": "Server starts but Form parsing still fails at runtime.",
      "fail_rate": 0.8,
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "why_fails": "Breaks form clients; still 422 for the other content type.",
      "fail_rate": 0.65,
      "condition": "",
      "sources": []
    }
  ],
  "workarounds": [
    {
      "action": "",
      "success_rate": 0.95,
      "how": "pip install python-multipart  # required for Form/File",
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "success_rate": 0.9,
      "how": "async def login(username: str = Form(...), password: str = Form(...))  # and client must send application/x-www-form-urlencoded",
      "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": 0.85,
  "fix_success_rate": 0.8,
  "resolvable": "true",
  "first_seen": "2024-10-15",
  "last_confirmed": "2025-01-01",
  "last_updated": "2025-01-01",
  "evidence_count": 0,
  "tags": [],
  "locale": "en",
  "aliases": []
}