[flask] ORM one-to-one relationship

stay sqlalchemy in , If you want to map two models into a one-to-one relationship , Then it should be in the parent model , When specifying references , To pass a uselist=False Enter this parameter . Is to tell the parent model , When quoting this slave model in the future , It's no longer a list , It's an object .

Method 1 ： Refer to one to many Association , hold uselist=false, Add to objects without foreign keys , Others are the same as the previous one to many relationship

Configuration database 、 Create database engine 、 Create base class

from sqlalchemy import create_engine, Column, Integer, ForeignKey, String, TEXT, Boolean, DATE, DECIMAL
from sqlalchemy.ext.declarative import declarative_base
from datetime import date
from sqlalchemy.orm import sessionmaker,relationship,backref
#  Configuration variables of the 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 model class base class 
Base=declarative_base(engine)

# establish session object 
session=sessionmaker(engine)()

Create model classes

class Person(Base):
    __tablename__='t_person'  # Create table name , It is best to t_ start 
    id=Column(name='id',type_=Integer,primary_key=True,autoincrement=True)
    name=Column(name='name',type_=String(255))
    age=Column(name='age',type_=Integer)
    address=Column(name='address',type_=String(255))
    country=Column(name='country',type_=String(50))
    city=Column(name='city',type_=String(50))

    #  The ID card corresponding to the current person 
    id_card=relationship('ID_Card')

    def __str__(self):
        return f'Person- Number {
    self.id} full name {
    self.name} Annual collar {
    self.age}

class ID_Card(Base):
    __tablename__ = 't_id_card'
    card_number = Column(name='card_number', type_=String(18), primary_key=True)
    p_id=Column(Integer,ForeignKey('t_person.id'))

    #  Indicates the person corresponding to the ID card 
    person=relationship('Person')

    def __str__(self):
        return f"ID_Card- ID number {
      self.card_number}"

Query data

1、 Query name python Identity card number ：

def select():
    
    p1=session.query(Person).filter(Person.name=='python').first()
    print(p1)                       # Name is python Your character information 
    print(p1.id_card)               # Name is python Your ID card information 
    print(p1.id_card.card_number)   # Name is python Identity card number 

Person- Number 1 full name python Annual collar 18
ID_Card- ID number 112121212
112121212

2、 Check the ID number 112121212 Who is it? ？

def select():
    # Check the ID number 112121212 Who is it? ？
    id1=session.query(ID_Card).filter(ID_Card.card_number=='112121212').first()
    print(id1)                      # The ID card is 112121212 Your ID card information 
    print(id1.person)               # The ID card is 112121212 Your character information 
    print(id1.person.name)          # The ID card is 112121212 Character name of 

ID_Card- ID number 112121212
Person- Number 1 full name python Annual collar 18
python

Method 2 ： Recommended
Particular attention ：uselist=False: tell id_card It's not a list

 Human information table 
class Person(Base):
    __tablename__='t_person'  # Create table name , It is best to t_ start 
    id=Column(name='id',type_=Integer,primary_key=True,autoincrement=True)
    name=Column(name='name',type_=String(255))
    age=Column(name='age',type_=Integer)
    phone = Column(name='phone', type_=String(11), unique=True)
    address=Column(name='address',type_=String(255))
    country=Column(name='country',type_=String(50))
    city=Column(name='city',type_=String(50))

    #  The ID card corresponding to the current person ,uselist=False: tell id_card It's not a list 
    #id_card=relationship('ID_Card',uselist=False)

    def __str__(self):
        return f'Person- Number {
      self.id} full name {
      self.name} Annual collar {
      self.age}'

 ID card form 
class ID_Card(Base):
    __tablename__ = 't_id_card'
    card_number = Column(name='card_number', type_=String(18), primary_key=True)
    p_id=Column(Integer,ForeignKey('t_person.id'))
       
    #  Indicates the person corresponding to the ID card ,
    person=relationship('Person',backref=backref('id_card',uselist=False))

    def __str__(self):
        return f"ID_Card- ID number {
      self.card_number}"

Particular attention 2：person=relationship(‘Person’,backref=backref(‘id_card’,uselist=False)) Writing

Query data

1、 Query name python Identity card number ：

def select():
    
    p1=session.query(Person).filter(Person.name=='python').first()
    print(p1)                       # Name is python Your character information 
    print(p1.id_card)               # Name is python Your ID card information 
    print(p1.id_card.card_number)   # Name is python Identity card number 

Person- Number 1 full name python Annual collar 18
ID_Card- ID number 112121212
112121212

2、 Check the ID number 112121212 Who is it? ？

def select():

    id1=session.query(ID_Card).filter(ID_Card.card_number=='112121212').first()
    print(id1)                      # The ID card is 112121212 Your ID card information 
    print(id1.person)               # The ID card is 112121212 Your character information 
    print(id1.person.name)          # The ID card is 112121212 Character name of 

ID_Card- ID number 112121212
Person- Number 1 full name python Annual collar 18
python

Update data

3、 Call your cell phone [phone] The ID number of the person of is changed to “666666666”

def update():
    res=session.query(Person).filter(Person.phone=='13888888888').first()
    res.id_card.card_number='666666666'
    session.commit()

4、 Number your ID card 3 Information about , The name of the person is changed to zhilong

def update():
    res1=session.query(ID_Card).filter(ID_Card.card_id==3).first()
    print(res1.person)
    res1.person.p_name='zhilong'
    session.commit()

Delete data

5、 Call your cell phone [phone] Delete the character information of

def delete():
    res2=session.query(Person).filter(Person.phone=='1311118').first()
    session.delete(res2)
    session.commit()

6、 Call your cell phone [phone] The identity card information of the person information is deleted

def delete():
    res2 = session.query(Person).filter(Person.phone == '1311115').first()
    print(res2.id_card)
    session.delete(res2.id_card)
    session.commit()

7、 Number your ID card 2 Delete the character information of

def delete():
    res3=session.query(ID_Card).filter(ID_Card.card_id==2).first()
    session.delete(res3.person)
    session.commit()

Problems that may occur when creating tables ：

sqlalchemy.exc.InvalidRequestError: On relationship ID_Card.person, ‘dynamic’ loaders cannot be used with many-to-one/one-to-one relationships and/or uselist=False.

Because lazy loading is added to the model class , The one-to-one mode does not require lazy loading
FALSE ：

id_card=relationship('ID_Card',backref=backref('person',lazy='dynamic',uselist=False))

The right is

id_card=relationship('ID_Card',backref=backref('person',uselist=False))