Contents
Cirrus Link Resources
Cirrus Link Website
Contact Us (Sales/Support)
Forum
Cirrus Link Modules Docs for Ignition 7.9.x
Inductive Resources
Ignition User Manual
Knowledge Base Articles
Inductive University
Forum
MQTT Engine Custom Namespaces, configured to parse the payload as JSON, do not handle changing JSON structures automatically due to the way JSON payloads are parsed.
Consider these two examples of changing payloads on the same topic:
(1) Two message payloads received sequentially on topic "a/b" at MQTT Engine where payload 2 has a modified element from message 1:
{ "level": "value1" }
{ "level": { "key": "value2" } }
MQTT Engine will initially create the tag with the tagpath of "[MQTT Engine]a/b/level" with a value of 'value1'.
Now, when the second payload arrives on the same topic, since MQTT Engine does not automatically delete tags, it will try to create the tag "[MQTT Engine]a/b/level/key" with a value of 'value2'. However, level at this point is a leaf tag, not a folder. So, the new leaf tag called 'key' can not be created.
(2) Two message payloads received sequentially on topic "a/b" at MQTT Engine where message 2 is a subset of message 1:
{ "level": "low" "temp": "45.0" "alarm": "on" }
At this point, MQTT Engine will create multiple tags with the tagpaths of:
{ "level": "high" "temp": "99.0" }
On the arrival of the second message, the two leaf tags 'level' and 'temp' will be updated so all tags will now look as follows:
When the second payload arrives on the same topic, since MQTT Engine does not automatically delete tags, it will not modify the tag "[MQTT Engine]a/b/alarm". It will remain as 'good' quality as well.