The json_emitter node

This node is used to produce data, that can be processed in a flow.

It can be used for debugging and testing/mocking purposes as well as produce default values for different kind of applications.

Starting with a given list of JSON strings (json structures in string format), this data can be emitted and/or modified on every emit in different ways:

determine, how data for output gets selected from the list of json inputs, see also select
modify the selected data with modifier lambda functions
output periodically with every, possibly adding a timing jitter, or have exactly 1 output with the one-shot parameter

experimental since 0.19.9: With the modify and modify_with parameters, certain fields in the json string(s) can be modified with every interval.

Examples

|json_emitter(
  ' {"condition": {"id": 0, "name": "OK"}, "condition_reason": ""} ',
  ' {"condition": {"id": 1, "name": "Warning"}, "condition_reason": "bad succer"} ',
  ' {"condition": {"id": 2, "name": "Error"}, "condition_reason": "something went really wrong!"} '
  )

Emit one of the three given json strings(selected randomly) every 5 seconds (default).

|json_emitter(
  ' {"condition": {"id": 0, "name": "OK"}, "condition_reason": ""} ',
  ' {"condition": {"id": 1, "name": "Warning"}, "condition_reason": "bad succer"} ',
  ' {"condition": {"id": 2, "name": "Error"}, "condition_reason": "something went really wrong!"} ' 
  )
.every(3s)
.select('seq')

Select one of the json strings in sequence every 3 seconds, starting with the first one. After the last json string has been selectect and outputted, start over with the first one again. Produces data-point items.

Using modifiers

|json_emitter(
  ' {"Current_Ph_A": 10.33, "Current_Ph_B": 10.53, "Current_Ph_C": 10.76} ' 
  )
.every(200ms)
.align(true)
.modify(
    'data.Current_Ph_A',
    'data.Current_Ph_B', 
    'data.Current_Ph_C'
     )
.modify_with(
    lambda: random_normal(), 
    lambda: "data.Current_Ph_A" + 0.45, 
    lambda: nth(random(4), [12.552, 44.2, 13.86, 16.22])
    )
.as('data')

Output the json data every 200ms, modifying it on every emit with the given lambda functions. Note the 'as' parameter here: It gives the output data a new root-object ('data') and the modifiers must target the 'rooted' fields.

Sample output:

{"ts":  1675147412200, "data":  
  {"Current_Ph_A": 1.6554763679823647, "Current_Ph_B": 2.105476367982365, "Current_Ph_C": 44.2}
}

Batch output and one_shot

def start_time = '2021-11-16T16:21:00.000Z'
|json_emitter(
  ' {"Current_Ph_A": 10.33, "Current_Ph_B": 10.53, "Current_Ph_C": 10.76} ',
  ' {"Current_Ph_A": 11.13, "Current_Ph_B": 10.74, "Current_Ph_C": 11.17} ',
  ' {"Current_Ph_A": 13.78, "Current_Ph_B": 11.02, "Current_Ph_C": 11.12} ',
  ' {"Current_Ph_A": 12.46, "Current_Ph_B": 10.98, "Current_Ph_C": 11.71} '
  )
.select('batch')
.one_shot(true)
.start_ts(start_time)

Output a data-batch item (using all the json items at once) exactly one time (one-shot), using start_time as timestamp. After the first output, the node will go to sleep for the rest of its life.

Parameters

Parameter	Description	Default
[node] json(`string_list`)	list of json strings
every(`duration`)	emit interval	5s
jitter(`duration`)	max random value for time jitter added to every, adds time jitter to the values produced	0ms
align(`bool`)	align the time to the every param, does not have an effect, if `start_ts` is given.	false
select(`string`)	entry select mode, possible values: `rand` or `seq`, `batch`	'rand'
start_ts(`string` or `int`)	Timestamp to start from, instead of wall clock time (default). ISO8601 datetime string or millisecond timestamp allowed here.	'2021-11-16T16:21:12.505Z'
modify(`string_list`)	list of fields, that should be modified	undefined
modify_with(`lambda_list`)	list of lambda expressions, that perform the modification on the fields given with `modify`	undefined
as(`string`)	root object used for output items	undefined
one_shot(`bool`)	when set to true, the node gives exactly 1 output, before it goes to sleep	false

Note : modify and modify_with must have the same number of parameters, if given.

select

value	Description	Resulting data-item
`rand`	randomly selects one of the json structures	data-point
`seq`	selects the json entries in sequence starting from top	data-point
`batch`	selects all of the entries resulting in a batch of data-points	data-batch