JSON Patch SQLAlchemy models w/ Flask

example.py

from dictalchemy import make_class_dictable
from flask import Flask, request, jsonify, json
from flask_sqlalchemy import SQLAlchemy
from jsonpatch import JsonPatch, JsonPatchException

app = Flask(__name__)
app.debug = True
db = SQLAlchemy(app)
make_class_dictable(db.Model)

@app.errorhandler(JsonPatchException)
def on_patch_exception(error):
    return jsonify({'message': 'Invalid JSON patch'}), 400

class Book(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(20))
    description = db.Column(db.Text)

def patch(instance, **kwargs):
    # Create the patch object
    patch = JsonPatch(request.get_json())
    # Get a dictionary instance of the model instance
    data = instance.asdict(exclude_pk=True, **kwargs)
    # Apply the patch to the  dictionary instance of the model
    data = patch.apply(data)
    # Apply the patched dictionary back to the model
    instance.fromdict(data)

@app.route('/books/<resource_id>', methods=['PATCH'])
def books(resource_id):
    book = Book.query.get_or_404(resource_id)
    patch(book)
    db.session.commit()
    return jsonify(book.asdict())

with app.app_context():
    db.create_all()
    db.session.add(Book(title='Title', description='Description'))
    db.session.commit()

client = app.test_client()

data = json.dumps([
    {'op': 'replace', 'path': '/title', 'value': 'New Title'},
    {'op': 'replace', 'path': '/description', 'value': 'New Description'}
])

response = client.patch('/books/1', content_type='application/json', data=data)
assert response.status_code == 200
print(response.data)
print('-' * 40)
data = json.dumps({'bogus': 'value'})
response = client.patch('/books/1', content_type='application/json', data=data)
assert response.status_code == 400
print(response.data)

requirements.txt

Flask-SQLAlchemy
dictalchemy
jsonpatch