Understanding Python metaclass series (4)

z417 2020-11-17 14:07:55
understanding python metaclass series

Write it at the front

In the previous chapter Understanding python The metaclass ( also called metaclass) Series of actual combat ( 3、 ... and ) It's done users class and users surface Field mapping for ;
Continue to enrich users class Before the operation of , It took us a chapter to complete mysql Link to ;
Please point out the mistakes .

Create a global connection pool , To avoid frequently opening and closing database connections

  • Because the query takes time , Plan to introduce asynchrony , namely async/await( I don't understand it doesn't matter , Think of it as plain code , It's just that it's called in a special way )

    $ pip3 install aiomysql # adopt pip install
  • establish Mysql class , Define static methods createPool

    import aiomysql
    class Mysql:
    async def createPool():
    ''' The connection pool is made up of global variables __pool Storage , By default, the encoding is set to utf8, Auto commit transaction '''
    global __pool
    __pool = await aiomysql.create_pool(
    host='localhost', # mysql Server address
    port=3306, # mysql Listening port
    user='root', # mysql user name
    password='passwd', # mysql password
    db='ormdemo', # mysql Instance name (database)
    charset='utf8', # Encoding settings
    autocommit=True, # Automatic submission insert/update/delete
    maxsize=10, # Connection pool upper limit
    minsize=1 # Connection pool lower limit
    print(' Create success ')
    except Exception as e:
    print(f' Connect mysql error :{e}')
    # Test code
    if __name__ == '__main__':
    import asyncio
    loop = asyncio.get_event_loop()
  • to Mysql class New static method selectexecute

    async def select(sql, args, size=None):
    ''' Pass in SQL Statement and SQL Parameters
    @sql : sql sentence
    @args: List of condition values
    @size: The result set size of the query
    print(f'{sql} ==> {args}')
    # Use with Context manager , Automatic execution close
    async with __pool.acquire() as conn:
    # acquire: Get connections from the free pool . if necessary , And the size of the pool is smaller than maxsize, Create a new connection .
    async with conn.cursor(aiomysql.DictCursor) as cur:
    # cursor: Connected cursor
    # DictCursor: A cursor that returns the result as a dictionary
    await cur.execute(sql.replace('?', '%s'), args or ())
    # sql.replace('?', '%s'): 'SELECT * FROM users WHERE uid=?'.replace('?', '%s')
    # args or (): 'SELECT * FROM users WHERE uid=%s' % (101,)
    if size:
    rs = await cur.fetchmany(size)
    rs = await cur.fetchall()
    print(f'rows returned: {len(rs)}')
    return rs
    async def execute(sql, args, autocommit=True):
    INSERT、UPDATE、DELETE operation , It's universal execute function ,
    Because of this 3 Kind of SQL The same parameters are required for the execution of , Returns an integer representing the number of rows affected
    print(f'{sql} ==> {args}')
    async with __pool.acquire() as conn:
    if not autocommit:
    await conn.begin() # Start to deal with
    async with conn.cursor(aiomysql.DictCursor) as cur:
    await cur.execute(sql.replace('?', '%s'), args)
    affected = cur.rowcount # Rows affected
    if not autocommit:
    await conn.commit() # Submit changes , Only when it is not submitted automatically
    except Exception as e:
    if not autocommit:
    await conn.rollback() # Roll back changes
    raise Exception(e)
    return affected

Under test select

if __name__ == '__main__':
import asyncio
loop = asyncio.get_event_loop()
rs = loop.run_until_complete(Mysql.select('select uid, name from users where uid=?', [101]))
  • Console output
 Create success
select * from users where uid=? ==> [101]
rows returned: 1
[{'uid': 101, 'name': 'z417'}]


  1. Defined Mysql class , Among them is 3 A static method

  2. Asynchronous is introduced , The calling method is divided into two steps


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