Developer Guide

Substitution Templates

You can use a substitution template to augment the JSON data returned when a rule is triggered and AWS IoT performs an action. The syntax for a substitution template is ${expression}, where expression can be any expression supported by AWS IoT in a SELECT or WHERE clause. This includes functions, operators, and information present in the original message payload. Because an expression in a substitution template is evaluated separately from the "SELECT ..." statement, you cannot reference an alias created using the AS clause. For more information about supported expressions, see AWS IoT SQL Reference.

Substitution templates appear in the SELECT clause within a rule:

{ "sql": "SELECT *, topic() AS topic FROM 'my/iot/topic'", "ruleDisabled": false, "actions": [{ "republish": { "topic": "${topic()}/republish", "roleArn": "arn:aws:iam::123456789012:role/my-iot-role" } }] }

If this rule is triggered by the following JSON:

{ "deviceid" : "iot123", "temp" : 54.98, "humidity" : 32.43, "coords" : { "latitude" : 47.615694, "longitude" : -122.3359976 } }

Here is the output of the rule:

{ "coords":{ "longitude":-122.3359976, "latitude":47.615694 }, "humidity":32.43, "temp":54.98, "deviceid":"iot123", "topic":"my/iot/topic" }