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Once a rule is created, you can write SQL statements to process the data in a certain type of topics. The IoT Hub console provides a simplified way to enter SQL statements.

For example, if you want to extract three fields action, targetDevice, and count from the JSON message in the E23VBC3GE8/device_02/event topic and then filter them by count <= 3 to get the final processed data for further forwarding, use the following rule:

Action

When you extract the desired fields from the topic, you should consider performing some operations on them, such as forwarding or storage. Currently supported operations include:

• Data forwarding to another topic
• Data forwarding to a third-party service
• Data forwarding to CKafka
• Data forwarding to a CMQ topic
• Data forwarding to a CMQ queue
• Data forwarding to CTSDB
• Data forwarding to TencentDB for MySQL
• Data forwarding to TencentDB for MongoDB

When triggering a forwarding action, the rule engine will encapsulate the payload reported by the device in JSON format as shown below:

1. JSON sample for forwarding to CMQ/CKafka:

   {
   "MsgType":    "Publish",
   "Topic":      "AD4GVS5549/device/data",
   "Seq":        13107192,
   "PayloadLen": 17,
   "Payload":    "dGhpcyBpcyBhIGV4YW1wbGU=", 
   "ProductId":  "AD4GVS5549",
   "DeviceName": "device",
   "Time":       "2018-08-14 15:12:05",
   }
   

   The descriptions of each field are as follows:
   • MsgType: valid values: Publish (forwarding to configured message queue), Forward (forwarding to the hit rule engine), StatusChange (status change).
   • PayloadLen: length of the payload of the message reported by the device in bytes.
   • Payload: payload of the original message, which will be Base64-encoded by default.
   • Event: it is present only for messages of the StatusChange type. Valid values: Online (connection), Offline (disconnection).
   • Time: the timestamp when the forwarding action is triggered.
2. JSON sample for forwarding to a third-party service (http forward):

   {
   "devicename":"device",
   "payload":{
     "params":{
      "power_switch":1,
      "color":1,
      "brightness":32
    }
   },
      "productid":"AD4GVS5549",
      "seq":2,
      "timestamp":1587109346,
      "topic":"AD4GVS5549/device/data"
   }
   

   The descriptions of each field are as follows:
   • devicename: device name defined on the IoT Hub platform.
   • payload: payload of the original message. If it is in JSON format, it will be passed through for forwarding; if it is in binary format, it will be Base64-encoded.
   • seq: internal auto-incrementing unique message identifier in int type.
   • timestamp: the Unix timestamp when the forwarding action is triggered.

Notes

Field definition

• A field can contain up to 300 asterisks, commas, dots, spaces, letters, and digits and cannot be empty.
• A field indicates the key in JSON. If the data is in binary format, the field cannot be used for filtering, and * can be used to forward all binary data.
• The reported JSON data can be in nested JSON format, such as {"device_status":{"switch":"on"}}, where device_status.switch can be used to get the value of switch.
• SQL and JSON subarrays are not supported.

Topic wildcard definition

If you want to listen on multiple topics, you can use # and + wildcards to define them.

• # represents 0 or more arbitrary topic segments, which can only be placed at the end of the topic.
• + represents 1 arbitrary topic segment, which can be placed in the middle of the topic.

For example, house_monitor/+/get

• Can listen on topics such as house_monitor/thermometer/get and house_monitor/door/get.
• Cannot listen on the topic house_monitor/door/switch/get, because + can represent only 1 topic segment.

For example, house_monitor/#

• Can listen on topics such as house_monitor/thermometer and house_monitor/door/switch/get.
• Cannot listen on house/#/get, because # can only be placed at the end of the topic.

Condition definition

The [condition] expression is used to filter messages in the topic. Only when a message satisfies the [condition] expression will it be extracted for further processing. Supported expressions are listed in the table below: