SQLALchemy操做MySQL關係型數據庫

1.SQLALchemy使用

• 安裝

pip install sqlalchemy；

• SQLAlchemy是Python編程語言下的一款開源軟件，是PythonSQL工具包和對象關係映射器，它爲應用程序開發人員提供了SQL的所有功能和靈活性

2.什麼是ORM

• ORM（Object Relational Mapper）就是把數據庫表的行與相應的對象創建關聯，互相轉換；

• 目前，最知名的Python ORM是SQLAlchemy和SQLobject；

3.數據庫操做

• 建立表使用create_all()方法，刪除表使用drop_all()方法，咱們一塊兒來看一下如何建立和刪除表

# 導入引擎模塊
from sqlalchemy import create_engine
# 導入基類模塊
from sqlalchemy.ext.declarative import declarative_base
# 導入字段類
from sqlalchemy import Column, Integer, String
# 導入會話模塊
from sqlalchemy.orm import sessionmaker

# 實體類的基類
Base = declarative_base()

# 實體類
class Teacher(Base):
    '''
    實體類的建立有兩個方面的用處：
    1：若是數據庫中沒有表，那麼能夠使用實體類建立
    2：若是數據庫中有表，實體類能夠映射表的結構，對錶的CRUD操做
    '''
    # 表名必須指定
    __tablename__ = 'teacher'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(255))
    age = Column(Integer)
    # 打印實例的使用能夠發現，數據也是保存在實體類實例的__dict__中
    def __repr__(self):
        # print(self.__dict__)
        return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)
    __str__ = __repr__

# 建立鏈接引擎
host = 'localhost'
port = 3306
username = 'zengzeng'
password = '123456'
db = 'XKD_Python_Course'
connect_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(connect_str, echo=True)

# 建立表
Base.metadata.create_all(engine)

# 刪除表
# Base.metadata.drop_all(engine)

咱們如今命令工具中查看一下數據庫中有沒有咱們想要的teacher表，上一篇文章中講過，先登陸mysql：mysql -uzengzeng -p123456，而後進入咱們要使用的數據庫：use XKD_Python_Course，咱們先經過：show tables;查看一下數據庫中的表，發現沒有teacher表 那如今就能夠執行代碼，建立數據庫了，建立好後咱們能夠在命令行查看一下：show tables;，發現teacher表已經存在了，建立表成功yes!

想要刪除剛剛建立的表，能夠使用drop_all()方法，執行代碼，再查看數據庫表，就能夠看teacher表已經被刪除了

Base.metadata.drop_all(engine)

• 插入數據使用session.add_all()方法；

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

Base = declarative_base()
class Teacher(Base):
    __tablename__ = 'teacher'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(255))
    age = Column(Integer)
    def __repr__(self):
        # print(self.__dict__)
        return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)
    __str__ = __repr__

host = 'localhost'
port = 3306
username = 'zengzeng'
password = '123456'
db = 'XKD_Python_Course'
connect_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(connect_str, echo=True)

# 建立會話，用於提交數據
Session = sessionmaker(bind=engine)
session = Session()

# 建立多行行實例，給表添加數據
try:
    lst = []
    for i in range(10):
        teacher = Teacher()
        teacher.name = 'zengzeng' + str(i)
        teacher.age = 20 + i
        lst.append(teacher)
        print(teacher)

    # session.add(student) 能夠添加一行記錄，也能夠添加多行記錄
    # 注意：這裏將行記錄實例添加到session，不會提交，須要手動提交
    session.add_all(lst)

except Exception as e:
    print('~~~~~~~~~~~'*200)
    session.rollback()
    print(e)
finally:
    session.commit()

咱們執行代碼，而後去命令工具查看一下表是否插入數據：select * from teacher;

• 查詢操做使用session.query()方法，迭代查詢；

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

Base = declarative_base()
class Teacher(Base):
    __tablename__ = 'teacher'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(255))
    age = Column(Integer)
    def __repr__(self):
        # print(self.__dict__)
        return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)
    __str__ = __repr__

host = 'localhost'
port = 3306
username = 'zengzeng'
password = '123456'
db = 'XKD_Python_Course'
conn_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(conn_str, echo=False)

Session = sessionmaker(bind=engine)
session = Session()

teacher_obj = session.query(Teacher)
for teacher in  teacher_obj:
    print(teacher) # 返回結果：{'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x1063125f8>, 'age': 20, 'name': 'nihao0', 'id': 1}
print('*'*300)

# 直接返回實例對象
teacher = session.query(Teacher).get(4)
print(teacher) # 返回結果：{'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x1075fd400>, 'age': 23, 'name': 'nihao3', 'id': 4}
print(teacher.id)  # 返回 aobama
print(teacher.name)
print(teacher.age)
print('*'*300)

# 返回的是可迭代對象
teacher_results = session.query(Teacher).filter(Teacher.id == 5)
for teacher in teacher_results:  # 拿到student實例對象
    print(teacher)

• 修改操做：session.update()；

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

Base = declarative_base()

class Teacher(Base):
    __tablename__ = 'teacher'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(255))
    age = Column(Integer)
    def __repr__(self):
        # print(self.__dict__)
        return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)
    __str__ = __repr__

# 建立鏈接引擎
host = 'localhost'
port = 3306
username = 'zengzeng'
password = '123456'
db = 'XKD_Python_Course'
conn_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(conn_str, echo=False)

# 建立會話，用於提交數據
Session = sessionmaker(bind=engine)
session = Session()

teacher = session.query(Teacher).get(4)
teacher.name = 'Robby'
teacher.age = '99'
session.commit()

where條件查詢

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, DATE, Enum, ForeignKey
import enum
from sqlalchemy.orm import sessionmaker
Base = declarative_base()
class My_Enum(enum.Enum):
    M = 'M'
    F = 'F'


# 實體類
class Emploee(Base):
    '''
    +------------+---------------+------+-----+---------+-------+
    | Field      | Type          | Null | Key | Default | Extra |
    +------------+---------------+------+-----+---------+-------+
    | emp_no     | int(11)       | NO   | PRI | NULL    |       |
    | birth_date | date          | NO   |     | NULL    |       |
    | first_name | varchar(14)   | NO   |     | NULL    |       |
    | last_name  | varchar(16)   | NO   |     | NULL    |       |
    | gender     | enum('M','F') | NO   |     | NULL    |       |
    | hire_date  | date          | NO   |     | NULL    |       |
    +------------+---------------+------+-----+---------+-------+
    '''
    __tablename__ = 'employees'
    emp_no = Column(Integer, primary_key=True, nullable=False)
    birth_date = Column(DATE, nullable=False)
    first_name = Column(String(14), nullable=False)
    last_name = Column(String(16),nullable=False)
    gender = Column(Enum(My_Enum), nullable=False)
    hire_date = Column(DATE, nullable=False)
    def __repr__(self):
        return "emp_no='%s', birth_date='%s', first_name='%s', last_name='%s', gender='%s', hire_date='%s'" % (self.emp_no, self.birth_date, self.first_name, self.last_name, self.gender, self.hire_date)
    __str__ = __repr__

# 建立鏈接引擎
host = 'localhost'
port = 3306
username = 'zengzeng'
password = '123456'
db = 'XKD_Python_Course'
conn_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(conn_str, echo=False)

# 建立表
Base.metadata.create_all(engine)

# 建立會話，用於提交數據
Session = sessionmaker(bind=engine)
session = Session()


# # 簡單的where條件查詢過濾， 返回可迭代對象, AND 取與
emploees = session.query(Emploee).filter(Emploee.emp_no < 10010).filter(Emploee.gender == 'M')
emploees = session.query(Emploee).filter((Emploee.emp_no > 10010) & (Emploee.gender == 'F'))

# OR 取並
emploees = session.query(Emploee).filter((Emploee.emp_no > 10010) | (Emploee.gender == 'F'))

# NOT 取反
emploees = session.query(Emploee).filter(~(Emploee.emp_no > 10010))

# in
emploees = session.query(Emploee).filter(Emploee.emp_no.in_([10010, 10011, 10012]))

# not in
emploees = session.query(Emploee).filter(~Emploee.emp_no.in_([10010, 10011, 10012]))

# like ，like能夠忽略大小寫進行模式匹配
emploees = session.query(Emploee).filter(Emploee.last_name.like('B%'))

for emploee in emploees:
    print(emploee)

order排序

• asc()：升序；

例如：
emploees = session.query(Emploee).filter(Emploee.last_name.like('B%')).order_by(Emploee.emp_no.asc())

• desc()：降序；

例如：
emploees=session.query(Emploee).filter(Emploee.last_name.like('B%')).order_by(Emploee.emp_no.desc())

• 多字段排序：在語句裏面進行屢次排序；

聚合與分組

• list()：轉化爲列表；

• count()：聚合count(*)查詢；

• all()： 轉化爲列表；

• limit().one()：查詢首行；

emploees = session.query(Emploee)
print(list(emploees))         # 轉化爲列表
print(emploees.count())     # 聚合count(*)查詢
print(emploees.all())        # 轉化爲列表
print(emploees.limit(1).one())    # 查詢首行

• max()：返回最大值；

• min()：返回最小值；

• avg()：返回平均值；

emploees = session.query(func.max(Emploee.emp_no))
emploees = session.query(func.min(Emploee.emp_no))
emploees = session.query(func.avg(Emploee.emp_no))

• group_by()：分組查詢；

emploees = session.query(func.count(Emploee.emp_no)).group_by(Emploee.gender)
print(emploees)
for emploee in emploees:
    print(emploee)

參考：https://www.9xkd.com/user/plan-view.html?id=2415909403