OpenStack Nova 之使用SQLAlchemy 操作 Mysql 示例

SQLAlchemy 簡介 【鏈接】

The SQLAlchemy Object Relational Mapper presents a method of associating user-defined Python classes with database tables, and instances of those classes (objects) with rows in their corresponding tables. It includes a system that transparently synchronizes all changes in state between objects and their related rows, called a unit of work, as well as a system for expressing database queries in terms of the user defined classes and their defined relationships between each other.

我的理解是，SQLAlchemy 是實體/關系映射的一種操作數據的方式， 實體是由Python所編寫的類， 這個類的每一個實體，就對應於數據庫中的每一條元組（行數據）。其中對這個類的實體的操作，直接映射（影響）到數據庫中對應的元組， 這種方式叫做 工作單元（操作單元，有點類似於一個原子操作把）

自己寫的查詢Flavor 的樣例

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, Float, Boolean

sql_connection = "mysql://root:root@localhost/nova?charset=utf8" 
engine = create_engine(sql_connection, echo=True) #echo=True 設置該項后，可以打印出sql的執行過程
Session = sessionmaker(bind=engine)
session = Session()

class NovaBase():
    pass

BASE = declarative_base() # 用戶創建與DB映射的基類

class InstanceTypes(BASE, NovaBase):
    __tablename__ = "instance_types" # 數據庫中表的名稱
    id = Column(Integer, primary_key=True) #Column 用於定義數據表 "instance_types”的字段， 其參數是該字段的具體的類型
    name = Column(String(255))
    memory_mb = Column(Integer)
    vcpus = Column(Integer)
    root_gb = Column(Integer)
    ephemeral_gb = Column(Integer)
    flavorid = Column(String(255))
    swap = Column(Integer, nullable=False, default=0)
    rxtx_factor = Column(Float, nullable=False, default=1)
    vcpu_weight = Column(Integer, nullable=True)
    disabled = Column(Boolean, default=False)
    is_public = Column(Boolean, default=True)

flavors = session.query(InstanceTypes).all() #查詢數據表
for flavor in flavors:
    print flavor.id, flavor.name

代碼輸出

2013-05-15 18:41:10,928 INFO sqlalchemy.engine.base.Engine SELECT DATABASE()
2013-05-15 18:41:10,929 INFO sqlalchemy.engine.base.Engine ()
2013-05-15 18:41:10,933 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'character_set%%'
2013-05-15 18:41:10,934 INFO sqlalchemy.engine.base.Engine ()
2013-05-15 18:41:10,935 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'lower_case_table_names'
2013-05-15 18:41:10,936 INFO sqlalchemy.engine.base.Engine ()
2013-05-15 18:41:10,937 INFO sqlalchemy.engine.base.Engine SHOW COLLATION
2013-05-15 18:41:10,937 INFO sqlalchemy.engine.base.Engine ()
2013-05-15 18:41:10,946 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'sql_mode'
2013-05-15 18:41:10,946 INFO sqlalchemy.engine.base.Engine ()
2013-05-15 18:41:10,948 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2013-05-15 18:41:10,950 INFO sqlalchemy.engine.base.Engine SELECT instance_types.id AS instance_types_id, instance_types.name AS instance_types_name, instance_types.memory_mb AS instance_types_memory_mb, instance_types.vcpus AS instance_types_vcpus, instance_types.root_gb AS instance_types_root_gb, instance_types.ephemeral_gb AS instance_types_ephemeral_gb, instance_types.flavorid AS instance_types_flavorid, instance_types.swap AS instance_types_swap, instance_types.rxtx_factor AS instance_types_rxtx_factor, instance_types.vcpu_weight AS instance_types_vcpu_weight, instance_types.disabled AS instance_types_disabled, instance_types.is_public AS instance_types_is_public 
FROM instance_types
2013-05-15 18:41:10,950 INFO sqlalchemy.engine.base.Engine ()

1 m1.medium
2 m1.tiny
3 m1.large
4 m1.xlarge
5 m1.small
6 m1.nano
7 m1.micro

　　

Nova 中所對應的代碼結構

1. 1. nova/openstack/common/db/sqlalchemy/models.py 定義了SQLAlchemy 的基類， 所有的對數據的操作，通過該類中定義的方法來實現， 其子類，只需要調用相關的方法即可
   2. nova/db/sqlalchemy/models.py 定義了nova數據中的所有的表

以InstanceTypes 為例

 

BASE = declarative_base() # 與上一個類子中的方法一樣

class NovaBase(models.SoftDeleteMixin, models.ModelBase): #區別在這里， models 為1中定義的模塊
      pass

class InstanceTypes(BASE, NovaBase):
     __tablename__ = "instance_types" # 數據庫中表的名稱
     id = Column(Integer, primary_key=True) #Column 用於定義數據表 "instance_types”的字段， 其參數是該字段的具體的類型
     name = Column(String(255))
     memory_mb = Column(Integer)
     vcpus = Column(Integer)
     root_gb = Column(Integer)
     ephemeral_gb = Column(Integer)
     flavorid = Column(String(255))
     swap = Column(Integer, nullable=False, default=0)
     rxtx_factor = Column(Float, nullable=False, default=1)
     vcpu_weight = Column(Integer, nullable=True)
     disabled = Column(Boolean, default=False)
     is_public = Column(Boolean, default=True)