sqlalchemy的声明层ORM访问方式
sqlalchemy中可以利用声明层进行表格类的建立,并利用ORM对象进行数据库的操作及访问,另一种方式为显式的 ORM 访问方式。
主要的建立步骤包括:
1. 设置DSN连接网址;
2. 创建引擎,利用引擎对DSN进行连接;
3. 创建会话类并绑定到引擎,创建引擎实例;
4. 创建表类,由于使用声明层元数据;
5. 利用会话实例来进行数据库操作。
基本连接关系图:
下面是完整代码
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 from sqlalchemy import create_engine, MetaData 2 from sqlalchemy.ext.declarative import declarative_base 3 from sqlalchemy.sql.schema import Table, Column 4 from sqlalchemy.sql.sqltypes import Integer, VARCHAR 5 from sqlalchemy.orm import sessionmaker 6 7 Base = declarative_base() 8 9 # Set DSN 10 dsn = 'mysql+mysqldb://root:root@localhost/test_db' 11 12 # Create engine, get connection 13 eng = create_engine(dsn) 14 cnx = eng.connect() 15 16 # Make a Session class binded with engine 17 Session = sessionmaker(bind=eng) 18 # Generate a session instance 19 session = Session() 20 21 # Build up Table class 22 class Test_tb(Base): 23 __table__ = Table('test_tb', Base.metadata, 24 Column('id', Integer, primary_key=True), 25 Column('name', VARCHAR(8)) 26 ) 27 28 29 # Insert value 30 # session.add_all([Test_tb(id=6, name='Momo')]) 31 session.add(Test_tb(id=6, name='Momo')) 32 session.commit() 33 34 # Delete value 35 session.query(Test_tb).filter(Test_tb.id==6).delete() 36 session.commit() 37 38 session.add_all([Test_tb(id=7, name='Momo'), Test_tb(id=8, name='Kitkat')]) 39 session.commit() 40 # Update value 41 fr = session.query(Test_tb).filter_by(id=7).all() 42 for f in fr: 43 f.id = 9 44 session.query(Test_tb).filter(Test_tb.id==8).delete() 45 session.query(Test_tb).filter(Test_tb.id==9).delete() 46 session.commit() 47 48 re = session.query(Test_tb).all() 49 # Show value: Each r is a row in table 50 for r in re: 51 print(r.__dict__) 52 53 cnx.close()
分段分析
首先导入所需的模块,创建声明层基类
1 from sqlalchemy import create_engine, MetaData 2 from sqlalchemy.ext.declarative import declarative_base 3 from sqlalchemy.sql.schema import Table, Column 4 from sqlalchemy.sql.sqltypes import Integer, VARCHAR 5 from sqlalchemy.orm import sessionmaker 6 7 Base = declarative_base() 8 9 # Set DSN 10 dsn = 'mysql+mysqldb://root:root@localhost/test_db'
创建引擎,以及会话实例
1 # Create engine, get connection 2 eng = create_engine(dsn) 3 cnx = eng.connect() 4 5 # Make a Session class binded with engine 6 Session = sessionmaker(bind=eng) 7 # Generate a session instance 8 session = Session()
基于声明层创建表格类
1 # Build up Table class 2 class Test_tb(Base): 3 __table__ = Table('test_tb', Base.metadata, 4 Column('id', Integer, primary_key=True), 5 Column('name', VARCHAR(8)) 6 )
最后利用会话实例对表格进行操作
1 # Insert value 2 # session.add_all([Test_tb(id=6, name='Momo')]) 3 session.add(Test_tb(id=6, name='Momo')) 4 session.commit() 5 6 # Delete value 7 session.query(Test_tb).filter(Test_tb.id==6).delete() 8 session.commit() 9 10 session.add_all([Test_tb(id=7, name='Momo'), Test_tb(id=8, name='Kitkat')]) 11 session.commit() 12 # Update value 13 fr = session.query(Test_tb).filter_by(id=7).all() 14 for f in fr: 15 f.id = 9 16 session.query(Test_tb).filter(Test_tb.id==8).delete() 17 session.query(Test_tb).filter(Test_tb.id==9).delete() 18 session.commit() 19 20 re = session.query(Test_tb).all() 21 # Show value: Each r is a row in table 22 for r in re: 23 print(r.__dict__) 24 25 cnx.close()
最终运行结果
{'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x000000000489F320>, 'id': 3, 'name': 'eric'} {'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x000000000489F390>, 'id': 5, 'name': 'mock'}
相关阅读
1. 显式的 ORM 访问方式