Inner join with table aliases in Flask and Python
Let's say we have two tables in our database, orders and customers. We want to retrieve all the orders made by customers who live in the state of California, and also include the name of the customer in the result. Here's how we can do it using an inner join with table aliases:
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///mydb.db'
db = SQLAlchemy(app)
class Order(db.Model):
id = db.Column(db.Integer, primary_key=True)
customer_id = db.Column(db.Integer, db.ForeignKey('customer.id'))
amount = db.Column(db.Float)
class Customer(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(50))
state = db.Column(db.String(2))
orders = db.relationship('Order', backref='customer', lazy=True)
@app.route('/orders/california-names')
def get_orders_from_california_with_names():
orders = db.session.query(Order.amount, Customer.name)\
.join(Customer, Order.customer_id == Customer.id)\
.filter(Customer.state == 'CA').all()
return jsonify([{'amount': order[0], 'name': order[1]} for order in orders])
In this example, we define the Order and Customer models using SQLAlchemy. Then, in the get_orders_from_california_with_names route, we use table aliases to join the Order and Customer tables and retrieve the name of the customer:
db.session.query(Order.amount, Customer.name)\
.join(Customer, Order.customer_id == Customer.id)
We use the .join() method to perform an inner join between the Order and Customer tables, and we use the Order.customer_id == Customer.id expression to match records with the customer_id foreign key column in the Order table to the id primary key column in the Customer table. We also use the Customer.name column and table alias to retrieve the name of the customer.
Finally, we use the filter() method to filter customers by the state of California, and the all() method to retrieve all the matching orders and customer names. We use a list comprehension to format the results as a list of dictionaries, where each dictionary contains the order amount and the name of the customer.
Happy Learning!! Happy Coding!!
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