[flask] ORM one to many relationship

SQLAlchemy Provides a relationship, This class can define attributes , In the future, when accessing the associated table, you can access it directly through attribute access . in addition , Can pass backref To specify the attribute name of reverse access .

Configuration database 、 Create database engine 、 Create base class

# Configuration database 
HOSTNAME = '127.0.0.1'
PORT = '3306'
DATABASE = 'test'
USERNAME = 'root'
PASSWORD = 'root'
DB_URI = 'mysql+pymysql://{}:{}@{}:{}/{}?charset=utf8mb4'.format(USERNAME, PASSWORD, HOSTNAME, PORT, DATABASE)

# Create database engine 
engine=create_engine(DB_URI)

# Create base class , All model classes inherit the base class 
Base=declarative_base(engine)

# establish session
session=sessionmaker(engine)()

Method 1 ：

Create model classes

# Create model classes 
class Dept(Base):
    __tablename__='t_dept2'
    dept_no=Column(name='dept_no',type_=Integer,primary_key=True,autoincrement=True)
    dept_name=Column(name='dept_name',type_=String(20))
    city=Column(name='city',type_=String(20))
    
    # Represents the list of all employees in the current department , This way of writing is not the best , The best way to write is to associate in an object 
    emp=relationship('Emp') # The parameter must be the class name of another association model class 


    def __str__(self):
        return f' Department number :{
      self.dept_no} department :{
      self.dept_name} City :{
      self.city}'

Particular attention 1： The first 9 Line code ： Represents the list of all employees in the current department ; This way of writing is not the best , The best way to write is to associate in an object

class Emp(Base):
    __tablename__='t_emp2'
    emp_no=Column(name='emp_no',type_=Integer,primary_key=True,autoincrement=True)
    emp_name=Column(name='emp_name',type_=String(20))
    hire_date=Column(name='hire_date',type_=DATE)
    sal=Column(name='sal',type_=DECIMAL(10,2))

    #todo  Set the foreign key association , Add a field from the table , Specify which field of the table is the foreign key of this field . From the field of the foreign key in the table , It must be consistent with the primary key field type of the main table .
    dept_no=Column(ForeignKey('t_dept2.dept_no',ondelete='CASCADE'),name='dept_no',type_=Integer)
    
    # Information of the Department to which the employee belongs 
    dept=relationship('Dept')        # The parameter must be the class name of another association model class 

    def __str__(self):
        return f' Employee number :{
      self.emp_no} Employee name :{
      self.emp_name} The employee's entry time :{
      self.hire_date} Employee pay :{
      self.sal}'

Particular attention 2： Set the foreign key association , Add a field from the table , Specify which field of the table is the foreign key of this field . From the field of the foreign key in the table , It must be consistent with the primary key field type of the main table .

dept_no=Column(ForeignKey('t_dept2.dept_no',ondelete='CASCADE'),name='dept_no',type_=Integer)

Method 2 ： Comment the ninth line of code in method one , Just associate in a model class

# Create model classes 
class Dept(Base):
    __tablename__='t_dept2'
    dept_no=Column(name='dept_no',type_=Integer,primary_key=True,autoincrement=True)
    dept_name=Column(name='dept_name',type_=String(20))
    city=Column(name='city',type_=String(20))

    # Represents the list of all employees in the current department , This way of writing is not the best , The best way to write is to associate in an object 
    #emp=relationship('Emp') # The parameter must be the class name of another association model class 


    def __str__(self):
        return f' Department number :{
      self.dept_no} department :{
      self.dept_name} City :{
      self.city}'

class Emp(Base):
    __tablename__='t_emp2'
    emp_no=Column(name='emp_no',type_=Integer,primary_key=True,autoincrement=True)
    emp_name=Column(name='emp_name',type_=String(20))
    hire_date=Column(name='hire_date',type_=DATE)
    sal=Column(name='sal',type_=DECIMAL(10,2))

    #todo  Set the foreign key association , Add a field from the table , Specify which field of the table is the foreign key of this field . From the field of the foreign key in the table , It must be consistent with the primary key field type of the main table .
    dept_no=Column(ForeignKey('t_dept2.dept_no',ondelete='CASCADE'),name='dept_no',type_=Integer)

    # Information of the Department to which the employee belongs ,backref: Reverse associated attribute name 
    dept=relationship('Dept',backref='emp')        # The parameter must be the class name of another association model class 

    def __str__(self):
        return f' Employee number :{
    self.emp_no} Employee name :{
    self.emp_name} The employee's entry time :{
    self.hire_date} Employee pay :{
    self.sal}

Particular attention 3： The first 12 Line code ： Information of the Department to which the employee belongs ,backref: Reverse associated attribute name ,dept=relationship('Dept',backref='emp') Medium Dept It must be another associated class name

Particular attention 4：relationship,backref Import required
from sqlalchemy.orm import sessionmaker,relationship,backref

insert data

def save():
    d1=Dept(dept_name=' Information Department ',city=' Beijing ')
    session.add(d1)
    #session.commit()

    e1=Emp(emp_name='python',hire_date='2020-1-1',sal='8888.88',dept_no=1)
    session.add(e1)
    session.commit()

Query data ：

Inquire about 1： Check all employees in the finance department

d1=session.query(Dept).filter(Dept.dept_name==' Finance Department ').first()
print(d1)
for i in d1.emp:
    print(i)

 Department number :2 department : City of Finance Department : Shanghai 
 Employee number :5 Employee name :flask The employee's entry time :2022-02-06 Employee pay :7777.77
 Employee number :6 Employee name :django The employee's entry time :2021-12-12 Employee pay :10000.00

Inquire about 2： Query the information that the entry time of employees under the Department is greater than 2022 year , And the salary exceeds 8000 Employee information

d2=session.query(Emp).filter(Dept.dept_name==' Information Department ').filter(Emp.hire_date>'2022-01-01',Emp.sal>8000).first()
print(d2)

 Employee number :4 Employee name :jmeter The employee's entry time :2022-06-04 Employee pay :10000.00

Inquire about 3： Inquire about python The employee's Department

e1=session.query(Emp).filter(Emp.emp_name=='python').first()
print(e1)
print(e1.dept)

Inquire about 4： Query employees whose employment time is greater than 2022 year , And the salary exceeds 7000 Of the employees are in those departments

e2=session.query(Dept).filter(Emp.hire_date>'2022-1-1',Emp.sal>7000).all()
print(e2)
for i in e2:
    print(i)

[<__main__.Dept object at 0x000001BA5EF8BCA0>, <__main__.Dept object at 0x000001BA5EF8BF40>]
 Department number :1 department : Ministry of information city : Beijing 
 Department number :2 department : City of Finance Department : Shanghai 

Inquire about 5： Statistics on the Department of the highest paid employees

res13=session.query(Emp,func.max(Emp.sal)).first()[0]   # Employee number :2~ Employee name :james~ come from : Beijing ~ Salary :50000.00
print(res13)
print(type(res13))                                      #Emp object , You can call properties 
print(res13.dept)

Update data

Number the employee in the employee table as 18 The number of employees in the Department where the employee information is located is changed to 500

def update():
    res1=session.query(Emp).filter(Emp.emp_id==18).first()
    print(res1)
    res2=res1.dept
    print(type(res2))   	#<class '__main__.Dept'>
    res2.emp_count=500
    session.commit()

doubt ： I need some advice from bloggers ：

problem ： Statistics of the highest paid employees in each department , How to modify the following code ？？？

res15=session.query(Emp,func.max(Emp.sal)).group_by(Emp.dept_id).all()
print(res15)