【修改】：

1. __pool.get()改成__pool.acquire()，官方文档只看到了Pool.acquire()

2. create_args_string() 的实现

3. sql 语句'`<sql field>`'改成'<sql field>'，去掉了繁琐的``，因此也无需escaped_fields

4. sql 语句关键字一律大写

5. python 变量名、函数名一律采用下划线_连接

# -*- coding: utf-8 -*-
# @author xian_wen
# @date 5/26/2021 3:39 PM

import logging
import aiomysql


def log(sql, args=()):
    logging.info('SQL: %s' % sql)


async def create_pool(loop, **kwargs):
    logging.info('Create a database connection pool...')
    global __pool
    __pool = await aiomysql.create_pool(
        host=kwargs.get('host', 'localhost'),
        port=kwargs.get('port', 3306),
        user=kwargs['user'],
        password=kwargs['password'],
        db=kwargs['db'],
        charset=kwargs.get('charset', 'utf8mb4'),
        autocommit=kwargs.get('autocommit', True),
        maxsize=kwargs.get('maxsize', 10),
        minsize=kwargs.get('minsize', 1),
        loop=loop
    )


# SELECT
async def select(sql, args, size=None):
    log(sql, args)
    global __pool
    async with __pool.acquire() as conn:
        async with conn.cursor(aiomysql.DictCursor) as cur:
            await cur.execute(sql.replace('?', '%s'), args or ())
            if size:
                # 获取指定数量的记录
                rows = await cur.fetchmany(size)
            else:
                # 获取所有记录
                rows = await cur.fetchall()
            logging.info('Rows returned: %s' % len(rows))
            return rows


# INSERT, UPDATE, DELETE
async def execute(sql, args, autocommit=True):
    log(sql)
    async with __pool.acquire() as conn:
        if not autocommit:
            await conn.begin()
        try:
            async with conn.cursor(aiomysql.DictCursor) as cur:
                await cur.execute(sql.replace('?', '%s'), args)
                affected = cur.rowcount
            if not autocommit:
                await conn.commit()
        except BaseException:
            if not autocommit:
                await conn.rollback()
            raise
        return affected


def create_args_string(num):
    return ', '.join(['?'] * num)


class Field(object):

    def __init__(self, name, column_type, primary_key, default):
        self.name = name
        self.column_type = column_type
        self.primary_key = primary_key
        self.default = default

    def __str__(self):
        return '<%s, %s:%s>' % (self.__class__.__name__, self.column_type, self.name)


class StringField(Field):

    def __init__(self, name=None, primary_key=False, default=None, ddl='varchar(100'):
        super().__init__(name, ddl, primary_key, default)


class BooleanField(Field):

    def __init__(self, name=None, default=False):
        super().__init__(name, 'boolean', False, default)


class IntegerField(Field):

    def __init__(self, name=None, primary_key=False, default=0):
        super().__init__(name, 'bigint', primary_key, default)


class FloatField(Field):

    def __init__(self, name=None, primary_key=False, default=0.0):
        super().__init__(name, 'real', primary_key, default)


class TextField(Field):

    def __init__(self, name=None, default=None):
        super().__init__(name, 'text', False, default)


class ModelMetaclass(type):

    def __new__(mcs, name, bases, attrs):
        # 排除 Model 类本身
        if name == 'Model':
            return type.__new__(mcs, name, bases, attrs)
        # 获取 table 名称
        table_name = attrs.get('__table__', None) or name
        logging.info('Found model: %s (table: %s)' % (name, table_name))
        # 获取所有的 Field 和主键名
        mappings = dict()
        fields = []
        primary_key = None
        for k, v in attrs.items():
            if isinstance(v, Field):
                logging.info('  Found mapping: %s ==> %s' % (k, v))
                mappings[k] = v
                # 判断 v 是否是主键
                if v.primary_key:
                    # 找到主键
                    if primary_key:
                        raise RuntimeError('Duplicate primary key for field: %s' % k)
                    primary_key = k
                else:
                    fields.append(k)
        if not primary_key:
            raise RuntimeError('Primary key not found.')
        for k in mappings.keys():
            attrs.pop(k)
        # 保存属性和列的映射关系
        attrs['__mappings__'] = mappings
        attrs['__table__'] = table_name
        # 主键属性名
        attrs['__primary_key__'] = primary_key
        # 除主键外的属性名
        attrs['__fields__'] = fields
        # 构造默认的 SELECT, INSERT, UPDATE 和 DELETE 语句
        attrs['__select__'] = 'SELECT %s, %s FROM %s' % (primary_key, ', '.join(fields), table_name)
        attrs['__insert__'] = 'INSERT INTO %s (%s, %s) VALUES (%s)' % (
            table_name, ', '.join(fields), primary_key, create_args_string(len(fields) + 1))
        attrs['__update__'] = 'UPDATE %s SET %s WHERE %s = ?' % (
            table_name, ', '.join(map(lambda f: '%s = ?' % (mappings.get(f).name or f), fields)), primary_key)
        attrs['__delete__'] = 'DELETE FROM %s WHERE %s = ?' % (table_name, primary_key)
        return type.__new__(mcs, name, bases, attrs)


class Model(dict, metaclass=ModelMetaclass):

    def __init__(self, **kwargs):
        # ** 传入关键字参数
        super().__init__(**kwargs)

    def __getattr__(self, key):
        try:
            return self[key]
        except KeyError:
            raise AttributeError(r"'Model' object has no attribute '%s'" % key)

    def __setattr__(self, key, value):
        self[key] = value

    def get_value(self, key):
        return getattr(self, key, None)

    def get_value_or_default(self, key):
        value = getattr(self, key, None)
        if value is None:
            field = self.__mappings__[key]
            if field.default is not None:
                value = field.default() if callable(field.default) else field.default
                logging.debug('Using default value for %s: %s' % (key, str(value)))
                setattr(self, key, value)
        return value

    @classmethod
    async def find_all(cls, where=None, args=None, **kwargs):
        """
        Find objects by WHERE clause.

        :param where:
        :param args:
        :param kwargs:
        :return:
        """
        sql = [cls.__select__]
        if where:
            sql.append('WHERE')
            sql.append(where)
        if args is None:
            args = []
        order_by = kwargs.get('order_by', None)
        if order_by:
            sql.append('ORDER BY')
            sql.append(order_by)
        limit = kwargs.get('limit', None)
        if limit is not None:
            sql.append('LIMIT')
            if isinstance(limit, int):
                sql.append('?')
                args.append(limit)
            elif isinstance(limit, tuple) and len(limit) == 2:
                sql.append('?, ?')
                # 在 args 末尾一次性添加 limit 中的所有值
                args.extend(limit)
            else:
                raise ValueError('Invalid limit value: %s' % str(limit))
        rows = await select(' '.join(sql), args)
        return [cls(**row) for row in rows]

    @classmethod
    async def find_number(cls, select_field, where=None, args=None):
        """
        Find number by SELECT and WHERE.

        :param select_field:
        :param where:
        :param args:
        :return:
        """
        sql = ['SELECT %s _num_ FROM %s' % (select_field, cls.__table__)]
        if where:
            sql.append('WHERE')
            sql.append(where)
        rows = await select(' '.join(sql), args, 1)
        if len(rows) == 0:
            return None
        return rows[0]['_num_']

    @classmethod
    async def find(cls, primary_key):
        """
        Find object by primary key

        :param primary_key:
        :return:
        """
        rows = await select('%s WHERE %s = ?' % (cls.__select__, cls.__primary_key__), [primary_key], 1)
        if len(rows) == 0:
            return None
        return cls(**rows[0])

    async def save(self):
        args = list(map(self.get_value_or_default, self.__fields__))
        args.append(self.get_value_or_default(self.__primary_key__))
        rows = await execute(self.__insert__, args)
        if rows != 1:
            logging.warning('Failed to insert record: affected rows: %s' % rows)

    async def update(self):
        args = list(map(self.get_value, self.__fields__))
        args.append(self.get_value(self.__primary_key__))
        rows = await execute(self.__update__, args)
        if rows != 1:
            logging.warning('Failed to update by primary key: affected rows: %s' % rows)

    async def remove(self):
        args = [self.get_value(self.__primary_key__)]
        print('args: %s' % args)
        rows = await execute(self.__delete__, args)
        if rows != 1:
            logging.warning('Failed to remove by primary key: affected rows %s' % rows)