FEEL context merge() function

[volodya327]

Hello, Everybody !
Could you help me, please, to understand what’s wrong with my FEEL context merge() function - “Union the given contexts. Returns a new context that includes all entries of the given contexts”.
I have two variables with JSON and I want to merge they together - just add property {“mainExec”:“1”} to “group01” in List.

var01=
{"documentDeadline":"2025-05-28T12:00:00",
"executors":{"execGroups":[
{"execGroup":"group01"},
{"execGroup":"group02"},
{"execGroup":"group03"}
]},
"documentId":"123456"}

var02=
{"executors":{"execGroups":[
{"execGroup":"group01","mainExec":"1"}
]}}

mergedDocument=context merge(var01, var02)

The result is not I expected:

mergedDocument=
{
	"documentDeadline": "2025-05-28T12:00:00",
	"executors": {
		"execGroups": [
			{
				"execGroup": "group01",
				"mainExec": "1"
			}
		]
	},
	"documentId": "123456"
}

Test diagram is here:
FEEL_context_merge_v03.bpmn (5.9 KB)

Maybe it’s possible to add param {“mainExec”:“1”} to “group01” in the List by using context put(context, key, value), but I have problems with this one too

[GotnOGuts]

Ohh… SNEAKY.

In Context functions | Camunda 8 Docs
there’s a small little note…

If an entry for the same key already exists in a context, it overrides the value. The entries are overridden in the same order as in the list of contexts.

Since both var1 and var2 have a path of /executors the executors from var2 is overwriting var1.

But I agree with you, that’s not how I would have understood it.
I would have expected the array of /executors/execGroups to be extended, and the key /executors/execGroups/execGroup{group1} to be overwritten.

Playing with it over on the Playground, even if /executors is changed to an array of values, it’s still overwritten, since the key (/executors) is still the same.

[hassang]

Hi @volodya327

The following FEEL expression should generate the expected result

{
  execGroupsItem1Removed: remove(var1.executors.execGroups, 1), // remove {"execGroup":"group01"}
  newExecGroups: insert before(execGroupsItem1Removed, 1, var2.executors.execGroups[1]), // insert {"execGroup":"group01","mainExec":"1"}
  result: {
    documentDeadline: var1.documentDeadline,
    executors: {
      execGroups: newExecGroups
    },
    documentId: var1.documentId
  }
}.result

[volodya327]

Thanks for your answers, Gentlemens !
So, is it possible to add item {“mainExec”:“1”} to {"execGroup":"group01"} in var01 variable and get a new one in the List like:
{"execGroup":"group01","mainExec":"1"}
If yes, then how to create var02 or maybe use another function ?

[hassang]

Hi @volodya327

The above expression generates exactly the output you are looking for, which in turn can be assigned to mergedDocument variable.

[volodya327]

Thanks, hassang for your solution !
I changed the names of var1 & var2 to var01 & var02 and it works.

But is it possible to make a solution for dynamic List when I don’t know index of item I want to modify ? Just by name.
Or, maybe, it’s possible to calculate the number of index by name ?

Anyway, thank you for this knowledge. I saw some undocumented possibilities for working with context, I can use in the future.

[hassang]

@volodya327

But is it possible to make a solution for dynamic List when I don’t know index of item I want to modify ?

Yes, you can find the index of the item using both Projection and Built-in function index of
https://docs.camunda.io/docs/components/modeler/feel/language-guide/feel-context-expressions/#projection
https://docs.camunda.io/docs/components/modeler/feel/builtin-functions/feel-built-in-functions-list/#index-oflist-match

Here is the expression to find the index of execGroup element with the value “group02”
index of(var01.executors.execGroups.execGroup,"group02")

[volodya327]

Thank you, hassang for your advises. They always very useful.
The final diagram, I tested the solution in Camunda 8.6 is here.
FEEL_JSON_merge+dynamic_index_Forum_solution.bpmn (8.1 KB)