[Pharo-users] How to write out simple Json?

Sven Van Caekenberghe sven at stfx.eu
Thu Feb 28 08:57:40 EST 2019


I really don't understand.

JSON needs Dictionaries and Arrays (or other Sequenceable Collections). That has nothing to do with Pharo or how NeoJSON or STONJSON are implemented - it is what defines JSON.

Of course, compatible objects work as well (NeoJSONObject is an example). You could make your own.

Since there is no literal syntax in Pharo for a Dictionary, you have to write something like

>>>  { #id->1. #name->'tim' } asDictionary

This has been discussed for years, I won't start that again. The above is short enough for me, but a bit of a pain when nesting.

Part of the power of Pharo is a very simple syntax, we can express an awful lot with very few constructs.

Your mapping examples won't work: you try to make something that is not a map but a list of associations into a map, that is simply not possible, sorry.

> On 28 Feb 2019, at 14:45, Tim Mackinnon <tim at testit.works> wrote:
> 
> Just to add more flavour to this - it seems quite wordy that we have to do this (or equivalent) to write some config. 
> 
> ex := OrderedDictionary new 
> 	at: 'track' put: 'pharo';
> 	at: 'language' put: 'smalltalk';
> 	at: 'exercises' put: (
> 		OrderedDictionary new
> 			at: 'slug' put: 'hello';
> 			at: 'id' put: 55;
> 			at: 'topics' put: #('a' 'b' 'c');
> 			yourself );
> 	yourself.
> 		
> String streamContents: [ :stream |
> 	(NeoJSONWriter on: (stream)) prettyPrint: true;
> 	mapInstVarsFor: Association;
> 	nextPut: ex ].
> 
> So I’m still wondering the NeoJSONObjectMapping can do something easy for Association other than simply mapInstVars?
> 
> 
>> On 28 Feb 2019, at 13:36, Tim Mackinnon <tim at testit.works> wrote:
>> 
>> Hi Sven - is there no convenience shortcut we can use in our code to make this less wordy when we are specifying it?
>> 
>> E.g. the following is very convenient to write - but doesn’t work (as you have $‘ and not $“ )
>> 
>> ex := { 'track'-> 'pharo'. 
>> 	'language' -> 'smalltalk'.
>> 	 'exercises' ->
>> 		{'slug' -> 'hello'.
>> 		'id' -> 55.
>> 		'topics' -> #('a' 'b' 'c') }
>> 		}.
>> 		
>> String streamContents: [ :stream |
>> 	(STONWriter on: (stream)) prettyPrint: true; 	writeList: ex ].
>> 
>> I had thought maybe NeoJSON might help and put:
>> 
>> String streamContents: [ :stream |
>> 	(NeoJSONWriter on: (stream)) prettyPrint: true;
>> 	"mapInstVarsFor: Association;"
>> 	nextPut: ex ].
>> 
>> But I get the error about missing an association mapping. If I uncomment that bit - I get things like: { "value" : “pharo" },
>> 
>> So is there a way I can write a simple mapper for Association that will write out the key in a string and the value in a string?
>> 
>> I’m quite suprised we can’t easily write out fragments of Json in our code in a light weight way? Or do I need to make a proper Config object and then teach it how to map properly such that rather than fiddling with our { x->y } dictionary sugar I do something like:
>> 
>> Config new at: ‘id’ is: 123; at: ‘name’ is: ‘Tim’; at: ‘exercises’ is: #(1 2 3).
>> 
>> And I guess at:is: can do the Association asDictionary thing?
>> 
>> But I thought Neo might give me something like that, as it must be terribly common?
>> 
>> Tim
>> 
>>> On 28 Feb 2019, at 13:16, Sven Van Caekenberghe <sven at stfx.eu> wrote:
>>> 
>>> STONJSON toString: { #id->1. #name->'tim' } asDictionary.
>>> 
>>> JSON cannot deal with Associations by themselves.
>>> 
>>>> On 28 Feb 2019, at 14:05, Tim Mackinnon <tim at testit.works> wrote:
>>>> 
>>>> I am stumped about how to write out some simple json (for a config file). I didn't think I need Neo, and STONJSON would be fine but it seems like creating items like: 
>>>> 
>>>> { 'id'-> self id. 'name' -> self name }
>>>> 
>>>> gives an error about the association. I think you have to do: { ('id'-> self id) asDictionary. ('name' -> self name) asDictionary } everywhere….
>>>> 
>>>> But when I switch over to NeoJsonWriter it also complains about Assocations too. I just want a simple output like:
>>>> { "id" : 12, "name" : "tim” }
>>>> 
>>>> I thought it was simple to do this? Am I missing something obvious.
>>>> 
>>>> Tim
>>> 
>>> 
>> 
>> 
> 
> 




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