AWS IoT Rule results in empty Payload

Question

My weather-station is publishing its status via MQTT to AWS IoT.

The message is published to topic $aws/things/my-weather-station-001/shadow/update and looks like this:

{
 "state": {
   "reported": {
      "temperature" : 22,
      "humidity" : 70,
       ....
      "wind" : 234,
      "air" : 345
   }
 }

After message is received I have create a rule to store it in AWS DynamoDB the rules select statement is:

SELECT state.reported.* FROM $aws/things/+/shadow/update/accepted

And when this works well, whilst I am sending messages containing state.reported field.

However sometimes to the topic $aws/things/weather-station-0001/shadow/update are sent "control" messages telling device to switch on an LED or some other part. These messages would be usually sent by an app or a controlling server and look like this notice that instead of reported field it hasdesired

{
 "state": {
   "desired": {
      "led1" : "on",
      "locked" : true
   }
 }

So when these messages are arriving, they ARE STILL processed by the rule and arrive to the DynamoDb table with {} empty payload.

Is there any way to force the Rule to ignore messages not containing state.reported element?

If you are trying to update the thing shadow over MQTT the topic should be $aws/things/<thing_name>/shadow/update — cementblocks
Thank you @cementblocks for your suggestion, however I believe you're incorrect in this case. In order to receive an update which is "confirmed" by AWS IoT you need to subscribe to $aws/things/<thing_name>/shadow/update/accepted or if you're interested in deltas to ../shadow/update/delta. If you subscribe only to ..shadow/update you are NOT really using shadows service, but simply getting back the update you sent (including when it is malformed). You can read more on that on docs.aws.amazon.com/iot/latest/developerguide/… — Dimitry K
This line in your question The message is published to topic $aws/things/my-weather-station-001/update and looks like this: has the incorrect topic, you should publish to $aws/things/my-weather-station-001/shadow/update — cementblocks
@cementblocks sorry, my bad. That was just a typo in the question (will fix it). The actual code is posting as you said to $aws/things/my-weather-station-001/shadow/update — Dimitry K

cementblocks cementblocks · Accepted Answer · 2016-03-14T20:33:11

You can add a where clause to your SQL statement. Try

SELECT state.reported.* FROM $aws/things/+/shadow/update/accepted WHERE state.reported <> ''

AWS IoT Rule results in empty Payload

1 Answers