In the preprocessor Add a function to create a JSON, add and remove JSON properties

[JohnLeyva]

The proposal is to add the following functions to the proprocesor

%json(jsonstring)
%json_set(jsonvar, propname, value)
%json_remove(jsonvar, propname)

The following provides some examples how it can be used.

card jsonExample [
    
    ' Creates a JSON from a string
    '!$r1 = %json('{ "a" : 1, "b" : "two" }')
    !$r1 = { "a" : 1, "b" : "two" }
    r1 = $r1

    ' Set a JSON child 
    '!$r2 = %json_set($r1,'c',3)
    !$r2 = { "a" : 1, "b" : "two", "c" : 3 } 
    r2 = $r2

    ' Set a JSON sub child 
    '!$r3_d = %json($r1,'{ "da" : 1, "db" : "two" }')
    !$r3_d = { "da" : 1, "db" : "two" }
    '!$r3 = %json_set($r1,"d",$r3_d)
    '   The following does not work at the moment
    '   !$r3 = { "a" : 1, "b" : "two", "d" : $r3_d }
    !$r3 = { "a" : 1, "b" : "two", "d" : { "da" : 1, "db" : "two" } }
    r3 = $r3

    !$r4_d_c = { "a" : [1,2] }
    '!$r4 = %json_set($r3.d,'dc',r3_d_c.a)
    !$r4 = { "a" : 1, "b" : "two", "d" : { "da" : 1, "db" : "two", "dc" : [1,2] } }
    r4 = $r4

    '!$r1 = %json_remove($r4,'d')
    !$r1 = { "a" : 1, "b" : "two" }
    r1 = $r1

    '!$r3_d = %json_remove($r4.d,'dc')
    !$r3_d = { "a" : 1, "b" : "two" }
    !$r3 = { "a" : 1, "b" : "two", "d" : { "da" : 1, "db" : "two" } }
    
    r3_d = $r3_d
    r3 = $r3
]

@The-Lum, I see you recentlu worked on the proprocessor so perhaps it is something of your interest

[The-Lum]

Hello @JohnLeyva, and all,

Just FYI, here are some pseudo-similar requests here:

• https://forum.plantuml.net/15436/allow-update-json-object-or-array-value
• https://forum.plantuml.net/17474/modify-json-variables-in-preprocessor
• https://forum.plantuml.net/18418/request-%25set_json_keys-function-json-writing-capabilities
• Dynamically create a json structure inside the preprecessor function #328

I actually worked on the preprocessor...
And I can try to look on that but I can't promise anything...
Step by step...

Regards,
Th.

[The-Lum]

Hello @JohnLeyva, and all,

Here is a fisrt proposal (I propose to change a little the function name...) with:

• %str2json('json_string')
• %json_add(jsonvar, propname, jsonvar) or %json_add(jsonvar, jsonvar_to_add)
• %json_remove(propname) or %json_remove(index)

Because it will be necessary to considering all JSON structures (Array, Object, Number, String, ...)...

---

And the fisrt tests (of the day...):

%str2json

%str2json('{"a": 1, "b": "two"}') = {"a":1,"b":"two"}

%json_add

On Object Context

%json_add({"a": 1, "b": "two"}, c, 3) = {"a":1,"b":"two","c":3} 
%json_add({"a": 1, "b": "two"}, d, {"da": 1, "db": "two"}) = {"a":1,"b":"two","d":{"da":1,"db":"two"}}

On Array Context

%json_add([0], "a") = [0,"a"]

%json_remove

On Object Context

%json_remove({"a": 1, "b": "two","c":3}, c) = {"a":1,"b":"two"}
%json_remove({"a":1,"b":"two","d":{"da":1,"db":"two"}}, d) = {"a":1,"b":"two"}

On Array Context

%json_remove([1,2,3], 0) = [2,3]

• What should we do when the index is negative? (nothing or from the end of the array.. ??)

---

• What do you think?

For debug purpose, it will be perhaps necessary to implement a print function (as %json_print, or %json2str)...

• What will be the better name?

Remains some bondaries and side effects checks... in order to commit and PR...

See you for next step...
Regards,
Th.

[The-Lum]

Hello everybody,

Here is a first dev. attempt with:

• feat: add new JSON builtin functions (%str2json, %json_add and %json_remove) #1742

Available on last snapshot (~v1.2024.5beta1).

• Could you test to confirm proper operation?

Enjoy,
Regards,
Th.

[matthew16550]

https://jsonpatch.com/ might provide some ideas and the RFC has a list of examples that could be helpful test cases.

Combining with @The-Lum proposal, perhaps:

%json_add(jsonvar, path, value)
%json_remove(jsonvar, path)

JSON Patch uses JSON Pointer to describe the locations but that is a different format than plantuml has been using so more thought needed.