title: Not being able to POST negative numbers by Postman, how to do that?
body: <p>I have a Python app that uses Postman to GET and POST data's to/from MongoDB. It is a simple GasStation app, but it let's us POST negative numbers. How to validate that doesn't allow negative numbers?</p>
  <pre><code>@server_api.route('/add_data', methods=['POST'])
  def receive_data():
      data_received = request.get_json()
      if &quot;PetrolCapacity&quot; not in data_received or &quot;DieselCapacity&quot; not in data_received:
          return Response(&quot;Bad arguments&quot;, 400)
      print(data_received)
      service.push_to_database(data_received)
      return Response(&quot;Data received successfully&quot;, 200)
  
  
  @server_api.route('/get_data', methods=['GET'])
  def return_data():
      last_element = service.query_last_element()
      print(last_element)
  
      data = last_element['PetrolCapacity']
      return data
  </code></pre>
  <p><a href="https://i.stack.imgur.com/2pC9O.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2pC9O.png" alt="Postman Data" /></a></p>