IBM Watson IoT Rules
- 15 Jul, 2019
Rules are key elements for an IoT solution. Using rules you can trigger an action or send an alert any kind of notification. IBM update his platform and now you can create rules using a graphical interface.
The key part of a rule is the expression that will be evaluate to true or false. The expression language are built using JSONata. JSONata is a lightweight query and transformation language for JSON data.
The point is that IBM are using JSONata v1.4x. and the current version of JSONata is v1.6.5. The versions have lots of difference. Yesterday i was writing a rule to get the hour for an event. If you are using v1.6.5 you can use the function $fromMilllis with picture. $fromMillis(1510067557121, ‘[H01]’, ‘-0500’) => “10” But Watson IoT are using v1.4x and $fromMillis doesn’t have the picture implemented. The only way i found is to manipulate strings and i got the following expression:
$number($substring($fromMillis($state.datahora),11,1)) < 1 and $number($substring($fromMillis($state.datahora),12,1)) < 3 ? $number($substring($fromMillis($state.datahora),12,1))+24-3 : $number($substring($fromMillis($state.datahora),11,1))*10+ $number($substring($fromMillis($state.datahora),12,1))-3 $state.datahora returns an epoch timestamp. This expression returns the hour on my timezone (-3). If anyone have a more elegant solution post on comments. I know my solution can’t be the better one, but it works.