08.6 元类实现简易ORM

# -*- coding: utf-8 -*-
# @Time : 2021/8/1 19:13
# @Author : zy7y
# @Gitee : https://gitee.com/zy7y
# @File : metaclass_orm.py
# @Project : PythonBooks
import numbers


# 数据描述符 定义
class Field:
    pass


class IntField(Field):
    def __init__(self, db_column, min_value=None, max_value=None):
        self._value = None
        self.db_column = db_column
        self.min_value = min_value
        self.max_value = max_value

        if min_value is not None:
            if not isinstance(min_value, numbers.Integral):
                raise ValueError("min_value 必须是 int 类型")
            elif min_value < 0:
                raise ValueError("min_value 必须 大于 0 ")
            if not isinstance(max_value, numbers.Integral):
                raise ValueError("max_value 必须是 int 类型")
            elif max_value < 0:
                raise ValueError("max_value 必须 大于 0 ")

    def __get__(self, instance, owner):
        return self._value

    def __set__(self, instance, value):
        self._value = value


class CharField(Field):
    def __init__(self, db_column, max_length=None):
        self._value = None
        self.db_column = db_column
        self.max_length = None

        if max_length is None:
            raise ValueError("max_length 不能为None")

    def __get__(self, instance, owner):
        print(owner)
        return self._value

    def __set__(self, instance, value):
        if not isinstance(value, str):
            raise ValueError("value 必须是 字符串")
        # if len(value) > self.max_length:
        #     raise ValueError("超出长度")


# 元类定义
class ModelMetaClass(type):
    """元类定义 把字段 和元类信息进行处理 在加到 类属性中"""
    def __new__(cls, name, bases, attrs, **kwargs):
        print(attrs)
        fields = {}  # 存字段
        for key, value in attrs.items():
            if isinstance(value, Field):
                fields[key] = value
        attrs_meta = attrs.get("Meta", None)
        _meta = {}  # 存元类数据
        db_table = name.lower()
        if attrs_meta is not None:
            table = getattr(attrs_meta, "db_table", None)
            if table is not None:
                db_table = table
            del attrs["Meta"]
        _meta["db_table"] = db_table
        attrs["_meta"] = _meta
        attrs["fields"] = fields

        return super().__new__(cls, name, bases, attrs, **kwargs)


class BaseModel(metaclass=ModelMetaClass):
    def __init__(self, *args, **kwargs):
        for key, value in kwargs.items():
            setattr(self, key, value)
        return super().__init__()

    def save(self):
        fields = []
        values = []
        for key, value in self.fields.items():
            db_column = value.db_column
            if db_column is None:
                db_column = key.lower()
            fields.append(db_column)
            value = getattr(self, key)
            values.append(value)

        sql = f"insert into {db_column} ({fields}) values ({values})"
        print(sql)


class User(BaseModel):
    name = CharField(db_column="name", max_length=10)
    age = IntField(db_column="age", min_value=0, max_value=100)

    class Meta:
        db_table = "user"


if __name__ == '__main__':
    user = User()
    user.name = "zy7y"
    user.age = 1
    user.save()