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CRUD - Create Record

Creating records means:

instantiate a model
add it to the session
commit

Example

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
 
app = Flask(__name__)
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///app.db"
 
db = SQLAlchemy(app)
 
 
class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
 
 
with app.app_context():
    db.create_all()
 
    user = User(username="ravi")
    db.session.add(user)
    db.session.commit()
 
    print(user.id)  # id is available after commit

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
 
app = Flask(__name__)
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///app.db"
 
db = SQLAlchemy(app)
 
 
class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
 
 
with app.app_context():
    db.create_all()
 
    user = User(username="ravi")
    db.session.add(user)
    db.session.commit()
 
    print(user.id)  # id is available after commit

Session basics

db.sessiondb.session holds pending changes
commit()commit() finalizes the transaction

If something fails, you can:

db.session.rollback()

db.session.rollback()

Common pitfalls

Forgetting commit()commit() (data doesn’t persist)
Not handling IntegrityErrorIntegrityError (unique constraint violations)
Doing heavy DB work inside request handlers without optimization

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