Flask-SQLAlchemy How to serialize ORM objects to avoid the 'Object of type User is not JSON serializable' error?

Flask-SQLAlchemy ORM Object Serialization: Avoid "Object of type User is not JSON serializable" error

In the combination of Flask and SQLAlchemy, directly serializing ORM objects to JSON often leads to Object of type User is not JSON serializable errors. This article will explain in detail how to solve this problem.

question:

Using the database model defined by Flask-SQLAlchemy (such as the User model), after obtaining data through User.query.all() , directly using the jsonify() function to return to the front end will raise the above error. This is because jsonify() cannot directly serialize SQLAlchemy's ORM object.

Solution:

To solve this problem, it is necessary to convert the ORM object to a JSON serializable format, such as a dictionary. We can add a to_dict() method to the model class:

 from sqlalchemy import Column, Integer, String
from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy() # Assuming you've initialized your SQLAlchemy instance

class User(db.Model):
    __tablename__ = 'users' # Replace 'users' with your table name
    id = Column(Integer, primary_key=True)
    app_key = Column(String(50), unique=True)
    secret = Column(String(120), unique=True)

    def __init__(self, app_key=None, secret=None):
        self.app_key = app_key
        self.secret = secret

    def to_dict(self):
        return {
            "id": self.id,
            "app_key": self.app_key,
            "secret": self.secret,
        }

Then, use to_dict() method in the Flask routing function to convert the object into a dictionary list, and then use jsonify() to return:

 from flask import Flask, jsonify

app = Flask(__name__)
# ... (your database configuration) ...

@app.route("/users")
def get_users():
    users = User.query.all()
    return jsonify([user.to_dict() for user in users])

if __name__ == '__main__':
    app.run(debug=True)

Through to_dict() method, User object is converted into a JSON serializable dictionary, thereby avoiding serialization errors and ensuring that the correct data is returned to the front end. This approach is a common and effective way to deal with SQLAlchemy ORM object serialization.

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