SQLAlchemy学习-2.query() 查询数据

前言

SQLAlchemy 使用 query() 方法查询数据

创建模型

接着前面一篇创建的模型

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

# 拼接配置dialect + driver://username:passwor@host:port/database
DB_URI = 'mysql+pymysql://root:123456@localhost:3306/web'
Base = declarative_base()


class Students(Base):
    __tablename__ = 'students'  # 数据库表名

    id = Column(Integer, primary_key=True)
    name = Column(String(20))
    fullname = Column(String(30))
    nickname = Column(String(30))

    def __repr__(self):
        return "" % (
                 self.name, self.fullname, self.nickname)
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创建session实例

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from xx.xx import Students

engine = create_engine('mysql+pymysql://root:123456@localhost:3306/web')
# 把当前的引擎绑定给这个会话
Session = sessionmaker(bind=engine)
# 实例化
session = Session()
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query() 查询

query() 查询会转换成对应的SQL 语句

# query()
r1 = session.query(Students)
print(r1)
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等价于

SELECT students.id AS students_id, students.name AS students_name, students.fullname AS students_fullname, students.nickname AS students_nickname 
FROM students
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query()可以只查询某个字段，多个字段逗号隔开

r2 = session.query(Students.name)
print(r2)
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等价于

SELECT students.name AS students_name 
FROM students
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all()查询全部数据

all()查询全部数据

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from xx.xx import Students

engine = create_engine('mysql+pymysql://root:123456@localhost:3306/web')
# 把当前的引擎绑定给这个会话
Session = sessionmaker(bind=engine)
# 实例化
session = Session()


all = session.query(Students).all()
print(all)
for item in all:
    print(item.name, item.fullname)
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运行结果

[,
 , 
]
yoyo yoyoketang
yoyo1 yoyoketang1
yoyo2 yoyoketang2
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all 查询的结果是一个list of Students对象

first() 返回查询结果第一个数据

first = session.query(Students).first()
print(first)
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运行结果

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filter()筛选过滤

filter()方法加筛选条件

# filter() 过滤
r1 = session.query(Students).filter(Students.name == 'yoyo')
print(r1)
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等价于以下sql

SELECT students.id AS students_id, students.name AS students_name, students.fullname AS students_fullname, students.nickname AS students_nickname 
FROM students 
WHERE students.name = %(name_1)s
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查询结果需加 all() 方法得到全部结果，或者 first() 方法得到第一个结果

# filter() 过滤
r1 = session.query(Students).filter(Students.name == 'yoyo').all()
print(r1)  # []
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以上查询类似于 SELECT * FROM ...,如果查询结果只需要某个字段，可以在query()方法指定字段名称

# filter() 过滤
r1 = session.query(Students.name).filter(Students.name == 'yoyo').all()
print(r1)  # [('yoyo',)]

r2 = session.query(Students.name, Students.fullname).filter(Students.name == 'yoyo').all()
print(r2)  # [('yoyo', 'yoyoketang')]
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字符串可以判断相等，数字类型的可以判断 >= 和 <=

r3 = session.query(Students.name).filter(Students.id >= 1).all()
print(r3)  # [('yoyo',), ('yoyo1',), ('yoyo2',)]
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and和or 多条件查询

在filter()中用,分隔多个条件表示and

r = session.query(Students.name).filter(Students.id >= 1, Students.name == 'yoyo').all()
print(r)  # [('yoyo',)]
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or_方法实现 or 条件查询

from sqlalchemy import or_

r = session.query(Students.name).filter(or_(Students.id >= 1, Students.name == 'yoyo')).all()
print(r)  # [('yoyo',), ('yoyo1',), ('yoyo2',)]
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order_by()排序

根据id倒叙

r4 = session.query(Students).order_by(Students.id.desc()).all()  # desc()表示倒序
print(r4)
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运行结果

[, 
,
]
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like 和 in

判断等于和不等于可以直接用 == 和 !=

like() 模糊匹配

r = session.query(Students.name).filter(Students.name.like('%yoyo%')).all()
print(r)  # [('yoyo',), ('yoyo1',), ('yoyo2',)]
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in_() 包含

r = session.query(Students.name).filter(Students.name.in_(['yoyo', 'yoyo1'])).all()
print(r)  # [('yoyo',), ('yoyo1',)]
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count() 计算个数

.count()方法统计查询个数

r = session.query(Students).count()
print(r)  # 3
r1 = session.query(Students).filter(Students.name == 'yoyo').count()
print(r1)  # 1
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切片

all()方法返回的是一个list，那就可以通过切片取一部分数据

# 返回前2条数据
r = session.query(Students.name).all()[:2]
print(r)  # [('yoyo',), ('yoyo1',)]
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delete() 删除数据

根据查询结果，调用delete()方法删除对应数据，需要执行session.commit()提交事务。

session.query(Students).filter(Students.name == 'yoyo').delete()
session.commit()
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update() 修改数据

update()方法，需要执行session.commit()提交事务

# 修改fullname
session.query(Students).filter(Students.name == 'yoyo1').update({'fullname': 'zhangsan'})
session.commit()

# 修改后查询
r = session.query(Students).filter(Students.name == 'yoyo1').all()
print(r)  # []
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从运行结果可以看到已经更新成功。