I was learning to create apis in flask and was following this link.
I hit the run button and the the code worked but gave this warning about marshmellow-sqlalchemy
I then opened postman and put the url "http://127.0.0.1:5000/api/users" 
And here is the issue, it says "message": "Did not attempt to load JSON data because the request Content-Type was not 'application/json'."
There is a similar post already on stackoverflow, but I couldn't bring out the proper similarity between the two, so pls help!!
I copied the entire code form the above mentioned link but here is a copy of the same:-
from flask import Flask, request, jsonify
from flask_sqlalchemy import SQLAlchemy
from flask_marshmallow import Marshmallow
from flask_restful import Resource, Api
app = Flask(__name__)
api = Api(app)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///users.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
db = SQLAlchemy(app)
ma = Marshmallow(app)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(32), unique=True)
password = db.Column(db.String(32))
first_name = db.Column(db.String(32))
last_name = db.Column(db.String(32))
age = db.Column(db.Integer)
def __init__(self, username, password, first_name, last_name, age):
self.username = username
self.password = password
self.first_name = first_name
self.last_name = last_name
self.age = age
class UserSchema(ma.Schema):
class Meta:
fields = ('id', 'username', 'password', 'first_name', 'last_name', 'age')
db.create_all()
user_schema = UserSchema()
users_schema = UserSchema(many=True)
class UserManager(Resource):
@staticmethod
def get():
try: id = request.args['id']
except Exception as _: id = None
if not id:
users = User.query.all()
return jsonify(users_schema.dump(users))
user = User.query.get(id)
return jsonify(user_schema.dump(user))
@staticmethod
def post():
username = request.json['username']
password = request.json['password']
first_name = request.json['first_name']
last_name = request.json['last_name']
age = request.json['age']
user = User(username, password, first_name, last_name, age)
db.session.add(user)
db.session.commit()
return jsonify({
'Message': f'User {first_name} {last_name} inserted.'
})
@staticmethod
def put():
try: id = request.args['id']
except Exception as _: id = None
if not id:
return jsonify({ 'Message': 'Must provide the user ID' })
user = User.query.get(id)
username = request.json['username']
password = request.json['password']
first_name = request.json['first_name']
last_name = request.json['last_name']
age = request.json['age']
user.username = username
user.password = password
user.first_name = first_name
user.last_name = last_name
user.age = age
db.session.commit()
return jsonify({
'Message': f'User {first_name} {last_name} altered.'
})
@staticmethod
def delete():
try: id = request.args['id']
except Exception as _: id = None
if not id:
return jsonify({ 'Message': 'Must provide the user ID' })
user = User.query.get(id)
db.session.delete(user)
db.session.commit()
return jsonify({
'Message': f'User {str(id)} deleted.'
})
api.add_resource(UserManager, '/api/users')
if __name__ == '__main__':
app.run(debug=True)
