sqlalchemy——基本操作

以下所有代碼片段都使用了統一的引用，該引用如下：

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

一、表結構設計

engine = create_engine("mysql+pymysql://root:root@localhost/study?charset=utf8", echo=True)  # 連接數據庫,顯示SQL語句

Base = declarative_base()  # 創建基類


class Student(Base):
    __tablename__ = 'students'  # 指定表名
    __table_args__ = {
        # "mysql_engine":"MyISAM",
        "mysql_charset":"utf8"
    }  
    # show create table students 可以查看建表語句;默認是Innodb,lating-1.如果想顯示中文需要修改指定建表的類型,同時,engine也要指定編碼格式
    id = Column(Integer, primary_key=True)  #指定主鍵
    name = Column(String(30))   #多個字段名
    gender = Column(Integer)
    std_id = Column(String(10))
    teacher = Column(String(30))

    def __str__(self):  #顯示對象的時候打印名字
        return self.name


Base.metadata.create_all(engine)  # 創建所有繼承自 Base 的類對應的表

sqlslchemy在數據庫中創建表之前，會先檢查該表是否存在，如果不存在，才會去創建新表。

class Student(Base):
    __tablename__ = 'students'  # 指定表名
    id = Column(Integer, primary_key=True)
    name = Column(String(30))
    gender = Column(Integer)
    std_id = Column(String(10))
    teacher = Column(String(30))
    **math = Column(Integer)**   #變量字段

    def __str__(self):
        return self.name

雖然新加了一個math 變量（字段），但是由於數據庫中已有students表，所以不會去創建新表，match字段也就不存在。

 

二、基本增刪改查

1.插入數據

Session = sessionmaker(bind=engine)  # 獲取 Session類
ses = Session()  # 獲取session對象

zhangsan = Student(name="zhangsan", gender=1, std_id='XS331', teacher='hanmeimei', math=90)
lisi = Student(name="lisi", gender=1, std_id='XS332', teacher='hanmeimei', math=10)
wangwu = Student(name="wangwu", gender=0, std_id='XS333', teacher='lilei', math=60)
zhaoliu = Student(name="zhaoliu", gender=0, std_id='XS337', teacher='lilei', math=80)
ses.add(zhangsan)  # 單條添加
ses.add_all([lisi, wangwu, zhaoliu])  # 批量添加
ses.commit()

 

2.修改數據

zhangsan = ses.query(Student).filter_by(name='zhangsan').first()  #先獲取對象
zhangsan.math = 91  #更改對象的屬性
ses.commit()   #提交

也可以在還創建數據的時候修改，就是在提交之前進行修改：

liqi = Student(name="liqi", gender=1, std_id='XS335', teacher='xiadonghai', math=100)   #實例化一個對象
ses.add(liqi)  #添加對象，也可以視作添加一條數據
liqi = ses.query(Student).filter_by(name='liqi').first()
liqi.gender = 0
ses.commit()

 在創建一個對象之后，未添加之前直接改變其屬性。

liqi = Student(name="liqi", gender=1, std_id='XS335', teacher='xiadonghai', math=100)
liqi.gender = 0
ses.add(liqi)
ses.commit()

 除此之外還可以使用update。

sess.query(Student).filter_by(name='liming').update({'gender':0})
sess.commit()

 

3.刪除

result = sess.query(Student).filter(Student.id == 1 ).delete()
sess.commit()
result = sess.query(Student).filter(Student.id == 2 ).first()
sess.delete(result)
sess.commit()

 

4.查詢

查詢操作在數據庫操作中總是最復雜的，下面介紹一些常用的操作。

（1）算術操作符

= 操作符
students_99 = sess.query(Student).filter_by(name ='zhangsan').all()
students_100 = sess.query(Student).filter(Student.name == 'zhangsan').all()
for i in students_100:
   print(i.name)

！= 操作符
student_101 = sess.query(Student).filter_by(name != 'liming').all()  # error
student_98 = sess.query(Student).filter(Student.name != 'liming').all()
for i in student_98:
  print(i.name)

 > ,<, <=, >=, 操作符
student_60 = sess.query(Student).filter(Student.math > 10).all()
student_61= sess.query(Student).filter_by(math>10).all()  # error
student_62 = sess.query(Student).filter(Student.math < 100).all()
student_63 = sess.query(Student).filter(Student.math <= 90).all()
student_64 = sess.query(Student).filter(Student.math >= 90).all()
student_64 = sess.query(Student).filter(Student.math <> 90).all()  # error
for i in student_60:
    print(i.math)
for i in student_62:
    print(i.math)
for i in student_63:
    print(i.math)
for i in student_64:
    print(i.math)

 

（2）模糊查詢

like 操作符  % 代表任意多個字符  _ 代表一個字符
student_17 = sess.query(Student).filter(Student.name.like("%i%")).all()
for i in student_17:
    print(i.name)
student_17_2 = sess.query(Student).filter(Student.name.like("%i_i")).all()
for i in student_17_2:
    print(i.name)

not like
student_70 = sess.query(Student).filter(~Student.name.like("%i_i")).all()
student_71 = sess.query(Student).filter(Student.name.notlike("%i_i")).all()
for i in student_70:
    print(i.name)
print(student_70 == student_71)

 

（3）區間選取

in 操作符
student_18 = sess.query(Student).filter(Student.name.in_(['zhangsan','lisi','wangwu'])).all()
for i in student_18:
    print(i.name)
not in
student_19 = sess.query(Student).filter(~Student.name.in_(['lisi'])).all()
student_19_2 = sess.query(Student).filter(Student.name.notin_(['lisi'])).all()
for i in student_19:
    print(i.name)
print(student_19 == student_19_2)

 

（4）分頁

student_10 = sess.query(Student).limit(2).offset(1).all()  #從第幾條開始選取幾條
student_11 = sess.query(Student).offset(1).limit(2).all()
student_12 = sess.query(Student)[1:3]
for i in student_10:
    print(i.id)
for i in student_11:
    print(i.id)
for i in student_12:
    print(i.id)

 

（5）排序

order_by 排序
student_33 = sess.query(Student).filter(text("math >= 10")).order_by(~text("math")).all()  # 逆序
student_33_2 = sess.query(Student).filter(text("math >= 10")).order_by(text("math")).all()  # 順序
student_33_2_1 = sess.query(Student).filter(text("math >= 10")).order_by(desc(text("math"))).all()  # 逆序
student_33_3 = sess.query(Student).order_by(desc(Student.math)).all()  # 逆序
student_33_4 = sess.query(Student).order_by(Student.math.desc()).all()  # 逆序
student_33_5 = sess.query(Student).order_by(~Student.math).all()  # 逆序
student_33_6 = sess.query(Student).order_by(Student.math).all()  # 順序
print(student_31)
print(student_32)
print("___"* 30)
for i in student_33:
    print(i.math)
print("___"* 30)
for i in student_33_2:
    print(i.math)
for i in student_33_3:
    print(i.math)
for i in student_33_4:
    print(i.math)
for i in student_33_5:
    print(i.math)
for i in student_33_6:
    print(i.math)

 

（6）分組

group_by 分組
student_39 = sess.query(Student).group_by(Student.gender == 1).count()
print(student_39)

 

（7）having：分組之后條件過濾

having
student_39_1 = sess.query(Student).group_by(Student.gender == 1).having(Student.math>60).all()
for i in student_39_1:
    print(i)

 

（8）計數

count
student_38 = sess.query(Student).filter_by(gender=1).count()
student_38_2 = sess.query(func.count(Student.name),Student.name).group_by(Student.name).all()
student_38_3 = sess.query(func.count(Student.name),Student.gender).group_by(Student.gender).all()
print(student_38_2)
print(student_38_3)

 

（9）去重

distinct
student_40 = sess.query(distinct(Student.name)).all()
for i in student_40:
    print(i)

 

（10）空值

是否為null
student_20 = sess.query(Student).filter(Student.name != None).all()
student_21 = sess.query(Student).filter(~Student.name.is_(None)).all()
student_22 = sess.query(Student).filter(Student.name.isnot(None)).all()
student_21_3 = sess.query(Student).filter(Student.name.is_('zhangsan')).all()  # error
student_21_2 = sess.query(Student).filter(Student.name.is_(1)).all()
for i in student_20:
    print(i.name)
print(student_20 == student_21 == student_22)

student_23 = sess.query(Student).filter(Student.math.is_(90)).all()
student_24 = sess.query(Student).filter(Student.math == None).all()

 

（11）邏輯操作

and
student_25 = sess.query(Student).filter(Student.gender == 1, Student.math > 70).all()
student_26 = sess.query(Student).filter(and_(Student.gender == 1, Student.math > 70)).all()  # 別忘了引入該方法
student_27 = sess.query(Student).filter(Student.gender == 1).filter(Student.math > 70).all()
for i in student_25:
    print(i.name)
print(student_25 == student_26 == student_27)

or
student_28 = sess.query(Student).filter(or_(Student.gender == 1, Student.math > 80)).all()
for i in student_28:
    print(i.name)

 

（12）text：原生sql語句

text  原生sql條件語句
student_31 = sess.query(Student).filter(text("name='lisi'")).first()  # 注意值為字符串時的寫法
student_32 = sess.query(Student).filter(text("id=1")).first()  # 注意值為 數字 的寫法
student_31 = sess.query(Student).filter(text("id>1 and math>10")).all()
for i in student_31:
    print(i.name)

text 插入變量
student_34 =sess.query(Student).filter(text("gender=:sex and math>:score")).params(sex=1, score=1).all()
for i in student_34:
    print(i.name)

from_statement 原生sql語句
student_35 = sess.query(Student).from_statement(text("select * from students where id=:id")).params(id=1).one()
student_36 = sess.query(Student).from_statement("select * from students where math>:score").params(score=10).all()
student_36_1 = sess.query(Student).from_statement("select * from students where math>10").all()
print(student_35)
for i in student_36:
    print(i.name)
print(student_36 == student_36_1)

 

（13）使用別名

student_7 = sess.query(Student.name.label('std_name')).all()
print(student_7)
for i in student_7:
    print(i.std_name)
    print(i[0])  # 第二種取值方式
student_8 = sess.query(Student.name).all()
print(student_8)
for i in student_8:
    print(i.name)
    print(i[0])

 

（14）取值

根據主鍵獲取對象
students_1 = sess.query(Student).get(1)
print(students_1

value指定要獲取的字段 返回的是生成器
students_3  = sess.query(Student).value(Student.name)
print(students_3)

values 指定多個字段 返回的是生成器
students_3_2  = sess.query(Student).values(Student.id,Student.name)
print(students_3_2)
for i in students_3_2:
    print(i)


一次獲取多個字段值
students_4 = sess.query(Student.name,Student.gender).all()
print(students_4)
for i in students_4:
    print(i)

后續添加的方式選擇要得到的字段結果
students_5 = sess.query(Student.name).add_columns(Student.gender).all()
print(students_5)
student_6 = sess.query(Student).filter_by(name="王大麻子").one()
print(student_6)

錯誤用法
error_1 = sess.query(Student).filter_by(and_(Student.id == 1, Student.name == 'lisi')).first()
error_2 = sess.query(Student).filter_by(and_(id=1, name='lisi')).first()
error_3 = sess.query(Student).filter(and_(id=1, name='lisi')).first()

one 有且只有一個，否則報錯
student_30 = sess.query(Student).filter(Student.id == 1).one()
print(student_30)
可以只有一個或者沒有，不能為多個結果，否則報錯
student_31 = sess.query(Student).filter(Student.id == 10).one_or_none()
print(student_31)

student_13 = sess.query(Student).filter_by(id=1).one_or_none()
student_14 = sess.query(Student).filter(Student.id == 1).one_or_none()
print(student_13)
print(student_14)

 

（15）chain鏈式調用

student_15 = sess.query(Student).filter_by(gender=1).filter(Student.math>80).all()
# student_15_2 = sess.query(Student).filter_by(gender=1).filter_by(math>80).all()  # error
student_16 = sess.query(Student).filter(Student.gender == 1).filter(Student.math>80).all()
for i in student_15:
    print(i.name)
for i in student_16:
    print(i.name)