Vitor

 

First clarification: There are two different serialization formats, json and STON. The content of a json file can only be number, Boolean, string, array, dictionary. STON is an extended form based on json, designed to represent (almost) any Smalltalk object.

 

Second clarification: What are you trying to do? Do you want to serialize data for your own use, to read back into your own Pharo app? Or do you want to export data in json format, so that other users, not using necessarily using Pharo, can import it? For the first case, STON is a very flexible and convenient system. For the second case, you must stick to strict json, using only the classes allowed in json.

 

Coming to your specific examples, Date is not a class allowed in json. This is not a limitation of NeoJson or STON, it is a limitation of the definition of json. If you want to include a Date in a json file, you must turn it into an instance of a permitted class. So you could write:

 

STON toJsonString: Date today asString.

 

The only complication here is, if the json is read by other users, they must understand the format generated by Date>>asString.

 

If you are using STON to serialise objects for your own use, you may want to exclude some instvars (e.g. block closures). This is described in the class comments to the STON-Core package. You need to include a class side message #stonAllInstVarNames in the class, which lists the names of the instvars that are to be serialized.

 

If you want to go deeper into STON, I think Sven has an article on his website telling the whole story. This maybe enough to get you started.

 

HTH

 

Peter Kenny

 

From: Pharo-users <[hidden email]> On Behalf Of Vitor Medina Cruz
Sent: 20 March 2020 01:20
To: Any question about pharo is welcome <[hidden email]>
Subject: [Pharo-users] Json encoding

 

Hello,

 

I know two projects of json encoding/decoding — NeoJson and STON.

 

In Java I have two most used ones too: Gson and Jackson. Using those I can simply pass any object and it they can convert to a json string, the former can't deal with cycles, the latter can with some little config.

 

NeoJson seems to be limited to primitives, for example, in Pharo 8 I can't run

 

NeoJSONWriter toString: (Date today)

 

Since I got:

 

NeoJSONMappingNotFound: No mapping found for Date in NeoJSONWriter

 

 

STON works fine with 

 

STON toString: (Date today).

 

but fail with:

 

STON toJsonString: (Date today).

 

Also, STON fails if I try to serialize an object which contains an instance variable pointing to a block closure. I didn't find out how to ignore these instance variable as it is unnecessary for what I need at the moment.

 

So, which lib for json or some object/string encoding/decoding should I be using on Pharo? Is there something better than those libs? Am I doing something wrong? My experience tells this should be simple, but it is not.

 

Thanks in advance,

Vitor