flask db model 更新错误

Question

I am creating a simple app using python/flask with mariadb

I am almost finishing my CRUD, however, the update is not working.

The code is:

from flask import Flask, request
from flask_sqlalchemy import SQLAlchemy
from datetime import datetime
import pymysql

pymysql.install_as_MySQLdb()

app = Flask(__name__)
db = SQLAlchemy(app)


app.config["SQLALCHEMY_DATABASE_URI"] = "mysql://{username}:{password}@{server}/{db}".format(username = 'root', password = '', server = 'localhost', db = 'baby-tracker')

class Event(db.Model):
    id = db.Column(db.Integer,primary_key=True)
    description = db.Column(db.String(100),nullable=False)
    

    def __repr__(self):
        return f"Event: {self.description}"
    
    def __init__(self,description):
        self.description = description

def format_event(event):
    return {
        "description": event.description,
        "id": event.id
        
    }

#Main page
@app.route('/')
def hello():
    return 'Hello mate!'

#Create an event
@app.route('/events', methods=["POST"])
def create_event():
    description = request.get_json('description')
    event = Event(**description)
    db.session.add(event)
    db.session.commit()
    return format_event(event)

#Get all events
@app.route('/events', methods=["GET"])
def get_events():
    events = Event.query.order_by(Event.id.asc()).all()
    event_list = []
    for event in events:
        event_list.append(format_event(event))
    
    return {"events": event_list}

#Get a single event
@app.route('/events/<id>', methods=["GET"])
def get_event(id):
    #Could do this: if request.method == 'GET':
    event = Event.query.filter_by(id=id).one()
    formatted_event = format_event(event)
    return formatted_event

#Get a single event
@app.route('/events/<id>', methods=["DELETE"])
def delete_event(id):
    event = Event.query.filter_by(id=id).one()
    db.session.delete(event)
    db.session.commit()
    return f'Event id {id} deleted'

#Update event
@app.route('/events/<id>', methods=["PUT"])
def update_event(id):
    event = Event.query.filter_by(id=id)
    description = request.get_json('description')
    event.update(dict(description = description))
    db.session.commit()
    formatted_event = format_event(event)
    return formatted_event

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

I am getting the following error for the PUT request:

JSON I am sending in the put request using postman:

{ "description": "new test" }

The error I get:

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\flask\app.py", line 2091, in __call__
    return self.wsgi_app(environ, start_response)
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\flask\app.py", line 2076, in wsgi_app
    response = self.handle_exception(e)
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\flask\app.py", line 2073, in wsgi_app
    response = self.full_dispatch_request()
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\flask\app.py", line 1518, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\flask\app.py", line 1516, in full_dispatch_request
    rv = self.dispatch_request()
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\flask\app.py", line 1502, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**req.view_args)
  File "C:\Users\PC\Documents\estudo_python\projeto_integrado\backend\app.py", line 77, in update_event
    event.update(dict(description = description))
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\sqlalchemy\orm\query.py", line 3300, in update
    execution_options={"synchronize_session": synchronize_session},
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\sqlalchemy\orm\session.py", line 1712, in execute
    result = conn._execute_20(statement, params or {}, execution_options)
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\sqlalchemy\engine\base.py", line 1705, in _execute_20
    return meth(self, args_10style, kwargs_10style, execution_options)
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\sqlalchemy\sql\elements.py", line 334, in _execute_on_connection 
    self, multiparams, params, execution_options
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\sqlalchemy\engine\base.py", line 1582, in _execute_clauseelement 
    cache_hit=cache_hit,
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\sqlalchemy\engine\base.py", line 1944, in _execute_context       
    e, statement, parameters, cursor, context
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\sqlalchemy\engine\base.py", line 2125, in _handle_dbapi_exception    sqlalchemy_exception, with_traceback=exc_info[2], from_=e
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\sqlalchemy\util\compat.py", line 208, in raise_
    raise exception
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\sqlalchemy\engine\base.py", line 1901, in _execute_context       
    cursor, statement, parameters, context
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\sqlalchemy\engine\default.py", line 736, in do_execute
    cursor.execute(statement, parameters)
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\pymysql\cursors.py", line 148, in execute
    result = self._query(query)
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\pymysql\cursors.py", line 310, in _query
    conn.query(q)
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\pymysql\connections.py", line 548, in query
    self._affected_rows = self._read_query_result(unbuffered=unbuffered)
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\pymysql\connections.py", line 775, in _read_query_result
    result.read()
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\pymysql\connections.py", line 1156, in read
    first_packet = self.connection._read_packet()
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\pymysql\connections.py", line 725, in _read_packet
    packet.raise_for_error()
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\pymysql\protocol.py", line 221, in raise_for_error
    err.raise_mysql_exception(self._data)
  File "C:\Users\PC\.virtualenvs\backend-_y8cE5wK\lib\site-packages\pymysql\err.py", line 143, in raise_mysql_exception
    raise errorclass(errno, errval)
sqlalchemy.exc.ProgrammingError: (pymysql.err.ProgrammingError) (1064, 'You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near \'\'description\': "\'new test\'"} WHERE event.id = \'1\'\' at line 1')
[SQL: UPDATE event SET description=%(description)s WHERE event.id = %(id_1)s]
[parameters: {'description': {'description': 'new test'}, 'id_1': '1'}]
(Background on this error at: https://sqlalche.me/e/14/f405)

I was getting I similar error with the POST event, but I solved it unpacking the dictionary with '**' tryed something similar with the PUT but haven´t get a positive result.

Answer 1

SqlAlchemy will not convert your structure to a string implicitly. You'll want to json.dumps() the value you're storing so it's a string and pass that into your event.update()

However, versions of MySQL do support JSON as a data type. If you create your column as JSON, then you can declare it in the SQLAlchemy model as JSON and then it will automatically handle the structure without you having to convert it to a JSON document.