python 學習筆記十一 SQLALchemy ORM(進階篇)

SqlAlchemy ORM　　

SQLAlchemy是Python編程語言下的一款ORM框架，該框架建立在數據庫API之上，使用關系對象映射進行數據庫操作，簡言之便是：將對象轉換成SQL，然后使用數據API執行SQL並獲取執行結果.

 

Python MySQL API (DBAPI)

通過 pymysql 連接管理mysql

create table students
    (
        id int  not null auto_increment primary key,
        name char(8) not null,
        sex char(4) not null,
        age tinyint unsigned not null,
        tel char(13) null default "-"
    );

1.插入數據

import pymysql

conn  = pymysql.connect("127.0.0.1",user='root',db='test') cur = conn.cursor() recount = cur.execute("insert into students(name,sex,age,tel) values('koka','man',18,'10000')") recount2 = cur.execute("insert into students(name,sex,age,tel) values('akok','man',20,'10010')") 

li = [    ("hehe","man",11,"110"), ("xixi","falme",12,"112")] recount3 = cur.executemany("insert into students(name,sex,age,tel) values(%s,%s,%s,%s)",li)

conn.commit()
cur.close()
conn.close()

  print(recount, recount2, recount3)

2.刪除數據

import pymysql 

conn = pymysql.connect("127.0.0.1",user='root',db='test') 
cur = conn.cursor()

recount = cur.execute("delete from students where name='akok';")

conn.commit()
cur.close()
conn.close()

3.修改數據

import pymysql 

conn = pymysql.connect("127.0.0.1",user='root',db='test') 
cur = conn.cursor()

recount = cur.execute("update students set age=24 where name='alex';")

conn.commit()
cur.close()
conn.close()

4.查數據

import pymysql 

conn = pymysql.connect("127.0.0.1",user='root',db='test') 
cur = conn.cursor()

recount = cur.execute("update students set age=24 where name='alex';") recount = cur.execute("select * from students;") print(cur.fetchone()) #匹配一條 print(cur.fetchone()) #cur.scroll(-1,mode="relative") #回退一條 print(cur.fetchone()) print(cur.fetchone()) cur.scroll(0,mode='absolute')#重置 print(cur.fetchone()) print(cur.fetchone())

conn.commit()
cur.close()
conn.close()

############################## fetchall  ##############################
import pymysql 

conn = pymysql.connect("127.0.0.1",user='root',db='test') 
cur = conn.cursor()
recount = cur.execute("select * from user;") nret = cur.fetchall() #所有查詢到的數據以元組返回 conn.commit() cur.close() conn.close() print(nret) for i in nret: print(i[0],i[1])

Dialect用於和數據API進行交流，根據配置文件的不同調用不同的數據庫API，從而實現對數據庫的操作，如：

MySQL-Python
    mysql+mysqldb://<user>:<password>@<host>[:<port>]/<dbname>
  
pymysql
    mysql+pymysql://<username>:<password>@<host>/<dbname>[?<options>]
  
MySQL-Connector
    mysql+mysqlconnector://<user>:<password>@<host>[:<port>]/<dbname>
  
cx_Oracle
    oracle+cx_oracle://user:pass@host:port/dbname[?key=value&key=value...]
  
更多詳見：http://docs.sqlalchemy.org/en/latest/dialects/index.html

步驟一：

使用 Engine/ConnectionPooling/Dialect 進行數據庫操作，Engine使用ConnectionPooling連接數據庫，然后再通過Dialect執行SQL語句。

from sqlalchemy import create_engine
import pymysql

engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/test",max_overflow=5)

engine.execute(
        "INSERT INTO hosts (hostname,ip_addr,port,group_id) VALUES ('web4','4.4.4.4',22,3)"
)

result = engine.execute("select * from hosts")

result.fetchall()

步驟二：

使用 Schema Type/SQL Expression Language/Engine/ConnectionPooling/Dialect 進行數據庫操作。Engine使用Schema Type創建一個特定的結構對象，之后通過SQL Expression Language將該對象轉換成SQL語句，然后通過 ConnectionPooling 連接數據庫，再然后通過 Dialect 執行SQL，並獲取結果。

from sqlalchemy import  create_engine, Table, Column, Integer, String, MetaData, ForeignKey, select
import pymysql

#生成metadata類
metadata = MetaData()

#創建user表，繼承metadata類
#Engine使用Schama Type創建一個特定的結構對象
user = Table("user", metadata,
             Column("id", Integer, primary_key=True),
             Column("name", String(20)))

color = Table("color", metadata,
              Column("id", Integer, primary_key=True),
              Column("name", String(20)))

#通過ConnectionPooling 連接數據庫
engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/test", max_overflow=5,echo=True)
#通過Dialect執行SQL
#metadata.create_all(engine) #創建表結構

增刪改查操作

""""增刪改查"""""
conn = engine.connect()

#conn.execute(user.insert(),{'id':2,"name":"koka"})
#conn.close()

#sql = user.insert().values(id=2, name='akok')
#conn.execute(sql)
#conn.close()

#sql = user.delete().where(user.c.id >1)
#conn.execute(sql)
#conn.close()

#sql = user.update().values(fullname=user.c.name)
#sql = user.update().where(user.c.name == "koka").values(name="okak")
#conn.execute(sql)
#conn.close()

#sql = select([user, ]) => selct * from user

#sql = select([user.c.id, ])=> select id from user

#sql = select([user.c.name,color.c.name]).where(user.c.id==color.c.id) =>
#SELECT user.name, color.name FROM user, color WHERE user.id = color.id

#sql = select([user.c.name]).order_by(user.c.name) =>
#SELECT user.name FROM user ORDER BY user.name

#sql = select([user, ]).group_by(user.c.name) =>
#SELECT user.id, user.name FROM user GROUP BY user.name

#conn.execute(sql)
#conn.close()

實例：

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

Base = declarative_base() #生成一個SQLORM基類

engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/test",echo=True)

class Host(Base):
    __tablename__ = "hosts"
    id = Column(Integer, primary_key=True, autoincrement=True)
    hostname = Column(String(64), unique=True, nullable=False)
    ip_addr = Column(String(128), unique=True, nullable=False)
    port = Column(Integer, default=22)

    def __repr__(self):
        return "<Host(hostname='%s',ip_addr='%s')>" % (self.hostname,self.ip_addr)

"""
# 無法刪除之前創建的hosts表，
# 這可能是MySQL在InnoDB中設置了foreign key關聯，造成無法更新或刪除數據。
# 可以通過設置FOREIGN_KEY_CHECKS變量來避免這種情況。
# SET FOREIGN_KEY_CHECKS = 0;

CREATE TABLE hosts (
    id INTEGER NOT NULL AUTO_INCREMENT,
    hostname VARCHAR(64) NOT NULL,
    ip_addr VARCHAR(128) NOT NULL,
    port INTEGER,
    PRIMARY KEY (id),
    UNIQUE (hostname),
    UNIQUE (ip_addr)
)
"""

#Base.metadata.create_all(engine) #創建所有表結構 metadata.create_all(engine)

if __name__ == "__main__":
    SessionCls = sessionmaker(bind=engine) 
    session = SessionCls()
    #h1 = Host(hostname="localhost", ip_addr="127.0.0.1")
    #h2 = Host(hostname="mysql", ip_addr="1.1.1.1", port=3306)
    #h3 = Host(hostname="web", ip_addr="10.0.0.10", port=8080)
    #session.add(h1)
    #h2.hostname = "mysqldb" #只要沒提交,此時修改也沒問題
    #session.add_all([h1, h2, h3])
    #session.rollback()
    #session.commit()

    res = session.query(Host).filter(Host.hostname.in_(["localhost", "mysqldb"])).all()
    print(res)
    """
    [<Host(hostname='localhost',ip_addr='127.0.0.1')>, <Host(hostname='mysqldb',ip_addr='1.1.1.1')>]
    """

更多內容詳見：

    http://www.jianshu.com/p/e6bba189fcbd

    http://docs.sqlalchemy.org/en/latest/core/expression_api.html

注：SQLAlchemy無法修改表結構，如果需要可以使用SQLAlchemy開發者開源的另外一個軟件Alembic來完成.

步驟三：

使用 ORM/Schema Type/SQL Expression Language/Engine/ConnectionPooling/Dialect 所有組件對數據進行操作。根據類創建對象，對象轉換成SQL，執行SQL。

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

engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/test", max_overflow=5, echo=True) #echo顯示sql語句創建過程

Base = declarative_base() #生成一個SQLORM基類

#創建表
class User(Base):
    __tablename__ = "users"
    id = Column(Integer, primary_key=True)
    name = Column(String(50))
    def __repr__(self):
        return "<User(id='%s',name='%s')>" % (self.id,self.name)

# 尋找Base的所有子類，按照子類的結構在數據庫中生成對應的數據表信息
#Base.metadata.create_all(engine)

if __name__ == "__main__":
    Session = sessionmaker(bind=engine)
    session = Session()
    #增
    #sql1 = User(id=1,name="haha")
    #sql2 = User(id=2,name="hehe")
    #session.add(sql1)
    #session.add_all([sql1, sql2])
    #session.commit()

    #改
    #session.query(User).filter(User.id >1).update({"name":"xixi"})
    #session.commit()

    #刪
    #session.query(User).filter(User.id == 1).delete()
    #session.commit()

    #查
    r1 = session.query(User).filter_by(name="xixi").first()

    r2 = session.query(User).filter_by(name="xixi").all()

    r3 = session.query(User).filter(User.name.in_(["haha", "hehe", "xixi"])).all()

    r4 = session.query(User.name.label("name_label")).all()
    #SELECT users.name AS name_label FROM users


    r5 = session.query(User).order_by(User.id).all()
    #SELECT users.id AS users_id, users.name AS users_name FROM users ORDER BY users.id

    r6 = session.query(User).order_by(User.id)[1:2]
    #SELECT users.id AS users_id, users.name AS users_name FROM users ORDER BY users.id LIMIT 1,2


    print(r1, r2, r3, r4, r5, r6)
    session.commit()

外鍵關聯

•  FOREIGN KEY 約束是大多數(但不是所有)的關系型數據庫中可以鏈接到主鍵列，或者擁有UNIQUE約束的列。
•  FOREIGN KEY 能夠引用多重列主鍵，並且其自身擁有多重列，被稱為“復合外鍵”(composite foreign key)。其也能夠引用這些列的子集(subset)。
•  FOREIGN KEY 列作為對於其引用的列或者行的變化的響應能夠自動更新其自。
•  FOREIGN KEY 能夠引用其自身的表，這個就涉及到“自引用”(self-referential)的外鍵了。

一多對關系表，一個主機屬於一個組，一個組可以擁有多個主機

from sqlalchemy import Table, Column, Integer, ForeignKey, create_engine, String
from sqlalchemy.orm import relationship,sessionmaker
from sqlalchemy.ext.declarative import declarative_base
import pymysql

engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/test", max_overflow=5)

Base = declarative_base()

class Host(Base):
    __tablename__ = 'host1'
    id = Column(Integer,primary_key=True,autoincrement=True)
    hostname = Column(String(64),unique=True,nullable=False)
    ip_addr = Column(String(128),unique=True,nullable=False)
    port = Column(Integer,default=22)
   group_id = Column(Integer, ForeignKey("group1.id")) #主機關聯組id
    #表示在group表中可以通過host_list查看host表內容，在host表中可以通過group查看group表內容
    group = relationship("Group", backref="host") 
    #group_list = relationship("Group",back_populates="host_list") #使用populates兩邊名稱要一致

class Group(Base):
    __tablename__ = "group1"
    id = Column(Integer, primary_key=True)
    name = Column(String(64),unique=True, nullable=False)
    #host_id = Column(Integer, ForeignKey("hosts.id")) #創建一個組就要指定一個主機id變成一對一的關系
    #host_list = relationship("Host",back_populates="group_list") #使用populates兩邊名稱要一致,兩個表對應設置名稱group_list和host_list

#Base.metadata.create_all(engine) #構建表

if __name__ == "__main__":
    SessionCls = sessionmaker(bind=engine)
    session = SessionCls()
    #建組
    g1 = Group(name="g1") g2 = Group(name="g2") g3 = Group(name="g3")
　　#建主機,關聯組
    h1 = Host(hostname="localhost1", ip_addr="127.0.0.1",group_id="1")
    h2 = Host(hostname="web2", ip_addr="192.168.1.10",group_id="2")
    h3 = Host(hostname="agent2", ip_addr="192.168.1.20",group_id="3")
    session.add_all([g1, g2, g3])
    session.add_all([h1, h2, h3])
    session.commit()
    #兩個表relationshap后，通過host表查詢h1記錄再通過group_id查找group表中對應的name
    h = session.query(Host).filter(Host.id == 1).first()
    print("h1:"h.group.name)
    session.commit()

映射關系

更多內容詳見：http://www.xker.com/page/e2015/04/179550.html

多對多關系表，需要第三張表關聯兩張表

from sqlalchemy import Table, Column, Integer, ForeignKey, and_, or_, func, create_engine, String
from sqlalchemy.orm import relationship, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
import pymysql

Base = declarative_base()

engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/test", max_overflow=5, echo=True)

Host2Group = Table("host_2_group",Base.metadata,
                   Column("host_id", ForeignKey("host.id"),primary_key=True),
                   Column("group_id", ForeignKey("group.id"),primary_key=True)
                   )

class Host(Base):
    __tablename__ = "host"
    id = Column(Integer, primary_key=True, autoincrement=True)
    hostname = Column(String(64), unique=True, nullable=False)
    ip_addr = Column(String(128), unique=True, nullable=False)
    port = Column(Integer, default=22)
    groups = relationship("Group",
                          secondary=Host2Group,
                          backref="host_list")
    #用於顯示查詢結果
    def __repr__(self):
        return "<id=%s, hostame=%s, ip_addr=%s>" %(self.id,
                                                   self.hostname,
                                                   self.ip_addr)

class Group(Base):
    __tablename__ = "group"
    id = Column(Integer, primary_key=True)
    name = Column(String(64),unique=True,nullable=False)

    def __repr__(self):
        return "<id=%s, name=%s>" % (self.id, self.name)

#Base.metadata.create_all(engine) #創建數據結構

if __name__ == "__main__":
    SessionCls = sessionmaker(bind=engine)
    session = SessionCls()
　　
    #創建組
    #h1 = Host(hostname="localhost",ip_addr="127.0.0.1")
    #h2 = Host(hostname="roomsvr",ip_addr="10.10.10.10")
    #session.add(h1)
    #session.add_all([h1, h2])

    #創建主機
    #g1 = Group(name='g1')
    #g2 = Group(name='g2')
    #g3 = Group(name='g3')
    #g4 = Group(name='g4')
    #session.add_all([g1,g2,g3,g4])
    #session.commit()

    #組和主機關聯
    groups = session.query(Group).all()
    g1 = session.query(Group).first()
    g2 = session.query(Group).filter(Group.name=="g2").first()
    h2 = session.query(Host).filter(Host.hostname=="localhost").first()
    h2.groups = groups #將主機同主機組關聯
    #h2.groups.append(groups)
    session.commit()
    
    #關聯表查詢
    print("=====>",h2.groups)
    print("=====g1>",g1.host_list)
    print("=====g2>",g2.host_list)
    #h2.groups.pop()
    session.commit()

join

  幾個Join的區別 http://stackoverflow.com/questions/38549/difference-between-inner-and-outer-joins 

• left join(左聯接) 返回包括左表中的所有記錄和右表中交集的記錄
• right join(右聯接) 返回包括右表中的所有記錄和左表中交集的記錄
• inner join(等值連接) 只返回兩個表中的交集字段

    #join 接上例代碼

    objs = session.query(Host).join(Host.groups).group_by(Group.name).all()#取兩個表的交集，按組名排序

    #SELECT * FROM host INNER JOIN host_2_group ON host.id = host_2_group.host_id
    #INNER JOIN `group` ON `group`.id = host_2_group.group_id GROUP BY `group`.id
    
    #count

    objs = session.query(Host, func.count(Host.hostname)).group_by(Host.id).all()

    #SELECT * count(host.hostname) FROM host GROUP BY host.id
    
    objs = session.query(Host,func.count(Group.name)).\
        join(Host.groups).group_by(Group.name).all()

    #SELECT host.id,host.hostname,host.ip_addr,host.port,count(`group`.name) as count_1 FROM host\
    #INNER JOIN host_2_group  ON host.id = host_2_group.host_id INNER JOIN `group` ON `group`.id = \
    #host_2_group.group_id GROUP BY `group`.name

    #print(objs)
    session.commit()

更多ORM內容:

http://files.cnblogs.com/files/wupeiqi/sqlalchemy.pdf.zip