Basic use of flask Sqlalchemy

1. rely on

pip install flask-sqlalchemy
pip install flask-script
pip install flask-migrate

2. establish SQLAlchemy object

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql+pymysql://root:[email protected]/sqlalchemy_test'  #  Bind database 
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True  #  Track changes to objects and signal without warning 
db = SQLAlchemy(app)

#  Code migration configuration 
manager = Manager(app)
migrate = Migrate(app, db)
manager.add_command('db', MigrateCommand)

3. Creating models

class User(db.Model):
    __tablename__ = "user_account"  #  Database table name 
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(30))
    fullname = db.Column(db.String(30))
    sex = db.Column(db.String(30))

    def __repr__(self):
        return f"User(id={
      self.id!r}, name={
      self.name!r}, fullname={
      self.fullname!r})"

class Address(db.Model):
    __tablename__ = "address"
    id = db.Column(db.Integer, primary_key=True)
    email_address = db.Column(db.String(30), nullable=False)
    user_id = db.Column(db.Integer, db.ForeignKey("user_account.id"), nullable=False) #  Define foreign key constraints 
    #  Define a relational model , It can be done by backref Take... In reverse 
    user = db.relationship('User', backref=db.backref('address', lazy=True), lazy=True)  
    def __repr__(self):
        return f"Address(id={
      self.id!r}, email_address={
      self.email_address!r})"

3.1 Common data types

Integer、String(size)、DateTime、Float、Boolean
More data types ：https://docs.sqlalchemy.org/en/14/core/type_basics.html#generic-types

3.2 db.Column Common configuration options

primary_key： If it is set to True, This column is the primary key of the table
unique： If it is set to True, Duplicate values are not allowed in this column
index： If it is set to True, Index this column , Improve query efficiency
nullable： If it is set to True, This column allows null values ; If it is set to False, Null values are not allowed in this column
default ： Define default values for this column
More configuration options ：https://docs.sqlalchemy.org/en/14/core/metadata.html#sqlalchemy.schema.Column

4. Perform the migration

#  Create migration warehouse -- initialization 
python manage.py db init
#  Create migration script 
python manage.py db migrate
#  Update the database 
python manage.py db upgrade
#  Fallback database 
python manage.py db downgrade  Version number 

Every time the database model changes , It needs to be reused migrate Command and upgrade command （ Combine in order ）, After successful use, the version number will be modified .

5. Inquire about API

User.query Back to a BaseQuery object , This object supports sqlalchemy Many queries for API

5.1. Common filters

filter() ： Add filter to original query , Return a new query
filter_by() ： Add equivalent filter to the original query , Return a new query
limit()： Limit the number of results returned by the specified query , Return a new query
offset()： Offset the result returned by the original query , Return a new query
order_by()： Sort the original query results according to the specified conditions , Return a new query
group_by()： Group the original query results according to the specified conditions , Return a new query

5.2 Common query execution functions

all()： Returns all results of the query as a list
first()： Returns the first result of the query , If there is no result , Then return to None
first_or_404()： Returns the first result of the query , If there is no result , Then terminate the request , return 404 Error response
get() ： Return the row corresponding to the specified primary key , If there is no corresponding line , Then return to None
get_or_404()： Return the row corresponding to the specified primary key , If the specified primary key is not found , Then terminate the request , return 404 Error response
count()： Number of returned query results
paginate()： Return to one Paginate object , It contains the results in the specified range

More inquiries API：https://docs.sqlalchemy.org/en/14/orm/query.html?highlight=cte#sqlalchemy.orm.Query