{
  "summary": [
    {"pkey": "id", "caption": "演示多人预览在线表", "tablename": "demo_presence", "module": "demo"}
  ],
  "fields": [
    {"name": "id", "type": "str(64)", "comment": "主键"},
    {"name": "session_id", "type": "str(64)", "comment": "演示会话ID"},
    {"name": "user_id", "type": "str(64)", "comment": "在线用户ID"},
    {"name": "user_name", "type": "str(64)", "comment": "在线用户名称"},
    {"name": "joined_at", "type": "datetime", "comment": "加入时间"},
    {"name": "last_seen_at", "type": "datetime", "comment": "最后活跃时间"}
  ],
  "indexes": [
    {"name": "idx_presence_session", "fields": ["session_id"]},
    {"name": "idx_presence_user", "fields": ["user_id"]}
  ],
  "codes": []
}