4种Python基于字段的不使用元类的ORM实现方法总结

class Field:
    def __init__(self, **kwargs):
        self.name = kwargs.get('name')
        self.column_type = kwargs.get('column_type')

    def __eq__(self, other):
        return Compare(self, '=', other)

    # 其他比较操作略...

class Compare:
    def __init__(self, left: Field, operation: str, right: Any):
        self.condition = f'`{left.name}` {operation} "{right}"'

    def __or__(self, other: "Compare"):
        self.condition = f'({self.condition}) OR ({other.condition})'
        return self

    def __and__(self, other: "Compare"):
        self.condition = f'({self.condition}) AND ({other.condition})'
        return self

class Model:
    def __init__(self, **kwargs):
        _meta = self.get_class_meta()

        for k, v in kwargs.items():
            if k in _meta:
                self.__dict__[k] = v

    @classmethod
    def get_class_meta(cls) -> Dict:
        if hasattr(cls, '_meta'):
            return cls.__dict__['_meta']
        _meta = {}

        for k, v in cls.__dict__.items():
            if isinstance(v, Field):
                if v.name is None:
                    v.name = k
                name = v.name
                _meta[k] = (name, v)

        table = cls.__dict__.get('__table__')
        table = cls.__name__ if table is None else table
        _meta['__table__'] = table

        setattr(cls, '_meta', _meta)

        return _meta

    def insert(self):
        _meta = self.get_class_meta()
        column_li = []
        val_li = []

        for k, v in self.__dict__.items():
            field_tuple = _meta.get(k)
            if field_tuple:
                column, field = field_tuple
                column_li.append(column)
                val = str(v) if field.column_type == 'INT' else f'"{str(v)}"'
                val_li.append(val)

        sql = f'INSERT INTO {_meta["__table__"]} ({",".join(column_li)}) VALUES ({",".join(val_li)});'
        print(sql)

class Query:
    def __init__(self, cls: Model):
        self._model = cls
        self._order_columns = None
        self._desc = ''
        self._meta = self._model.get_class_meta()
        self._compare = None
        self.sql = ''

    def _get(self) -> str:
        sql = ''

        if self._compare:
            sql += f' WHERE {self._compare.condition}'

        if self._order_columns:
            sql += f' ORDER BY {self._order_columns}'

        sql += f' {self._desc}'
        return sql

    def get(self, *args: Field) -> List[Model]:
        sql = self._get()
        table = self._meta['__table__']

        column_li = []

        if len(args) > 0:
            for field in args:
                column_li.append(f'`{field.name}`')
        else:
            for v in self._meta.values():
                if type(v) == tuple and isinstance(v[1], Field):
                    column_li.append(f'`{v[0]}`')

        columns = ",".join(column_li)
        sql = f'SELECT {columns} FROM {table} {sql}'
        self.sql = sql
        print(self.sql)

    def order_by(self, columns: Union[List, str], desc: bool = False) -> "Query":
        if isinstance(columns, str):
            self._order_columns = f'`{columns}`'
        elif isinstance(columns, list):
            self._order_columns = ','.join([f'`{x}`' for x in columns])

        self._desc = 'DESC' if desc else ''
        return self

    def where(self, compare: "Compare") -> "Query":
        self._compare = compare
        return self

class User(Model):
    name = Field()
    age = Field()

# 插入数据
user = User(name='Tom', age=24)
user.insert()

# 构建查询条件并查询数据
User.query().where((User.name == 'Tom') & (User.age >= 20)).order_by('age').get()

class Query:
    # ...

    def limit(self, num: int) -> "Query":
        self.sql += f' LIMIT {num}'
        return self

    def offset(self, num: int) -> "Query":
        self.sql += f' OFFSET {num}'
        return self

class Query:
    # ...

    def group_by(self, columns: Union[List, str]) -> "Query":
        if isinstance(columns, str):
            columns = [columns]
        self.sql += f' GROUP BY {",".join([f"`{x}`" for x in columns])}'
        return self

    def having(self, condition: Compare) -> "Query":
        self.sql += f' HAVING {condition.condition}'
        return self

class User(Model):
    name = Field()
    age = Field()

# 插入数据
user = User(name='Tom', age=24)
user.insert()

# 构建查询条件并查询数据
query = User.query().where((User.name == 'Tom') & (User.age >= 20)).order_by('age').limit(1).offset(0)
query.get(User.name, User.age)  # 仅查询指定字段

# 更复杂的查询
query = User.query().group_by('age').having((User.age > 20) & (User.age < 30)).order_by('age').limit(10).offset(0)
query.get(User.age, User.count(User.name))  # 查询年龄在20到30之间的用户数量