modify the project, everything go under app folder

app/models/__init__.py

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+from .base import Base
+
+from .user import User
+
+__all__ = ["Base", "User"]

app/models/base.py

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+import hashlib
+from sqlalchemy import Column, String
+from sqlalchemy.orm import declarative_base, declared_attr
+import ulid
+
+Base = declarative_base()
+
+# Base62 字符集
+ALPHABET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+
+
+def encode_base62(num: int) -> str:
+    """将一个整数编码为 Base62 字符串"""
+    if num == 0:
+        return ALPHABET[0]
+    arr = []
+    base = len(ALPHABET)
+    while num:
+        num, rem = divmod(num, base)
+        arr.append(ALPHABET[rem])
+    return "".join(reversed(arr))
+
+
+def encode_tablename_to_prefix(tablename: str, length: int = 3) -> str:
+    """
+    将表名 encode 成固定长度的前缀，使用 MD5 拿到表名的唯一哈希值，转为整数后用 Base62 截取前 N 位
+    """
+    # 计算表名的 MD5 哈希
+    hasher = hashlib.md5(tablename.encode("utf-8"))
+    hex_digest = hasher.hexdigest()
+    
+    # 将十六进制哈希转为大整数
+    num = int(hex_digest, 16)
+    
+    # 转为 Base62 字符串
+    b62_str = encode_base62(num)
+    
+    # 截取固定长度（例如 3 位）作为该表的专属代码
+    return b62_str[:length]
+
+
+def gen_convex_payload() -> str:
+    """生成 128位 ULID 转 Base62 的趋势递增 Payload"""
+    u = ulid.new()
+    return encode_base62(u.int)
+
+
+class AutoID:
+    """
+    全自动 Convex 风格 ID 注入器
+    不再需要手动定义任何 prefix，全自动根据 __tablename__ 编码生成
+    """
+    @declared_attr
+    def id(cls):
+        # 运行时动态获取子类的 __tablename__
+        tablename = cls.__tablename__
+        
+        # 将表名编码为固定前缀（例如 "users" -> "7X1"）
+        table_prefix = encode_tablename_to_prefix(tablename, length=3)
+        
+        # 核心工厂函数：拼接【编码后的表前缀】和【递增Payload】
+        def id_factory():
+            return f"{table_prefix}_{gen_convex_payload()}"
+
+        return Column(String(32), primary_key=True, default=id_factory)

app/models/message.py

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+from sqlalchemy import Column, DateTime, String, ForeignKey
+from sqlalchemy.sql import func
+from .base import Base, AutoID
+
+class Message(Base, AutoID):
+    __tablename__ = "messages"
+
+    user_id = Column(String, ForeignKey("users.id"), index=True)
+    content = Column(String)
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())

app/models/user.py

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+from sqlalchemy import Column, DateTime, String
+from sqlalchemy.sql import func
+
+from .base import AutoID, Base
+
+class User(Base, AutoID):
+    __tablename__ = "users"
+
+    google_id = Column(String, unique=True, index=True)
+    email = Column(String, unique=True, index=True)
+    name = Column(String)
+    avatar = Column(String)
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    def __repr__(self):
+        return f"<User(id={self.id}, name={self.name}, email={self.email})>"