Re: receiving POST encoded in JSON

[Scott Klement <web400@xxxxxxxxxxxxxxxx>]

Nathan,

did you look at the notes/examples in the "Working with JSON" handout on 
my site?
http://www.scottklement.com/presentations/Working%20with%20JSON%20in%20RPG.pdf

Does that provide enough information for you?

What yajl_stmf_load_tree() does is parse the JSON data into a set of 
data structures in memory.  So once this is complete, it is no longer in 
JSON format, now it is just structures in memory.  The pointer returned 
(docNode) is a pointer to the document node of this memory tree.  from 
that, you can get it's child nodes.  From those child nodes, you can go 
deeper and get their child nodes, etc.

You don't necessarily have to know the structure of the document in 
advance, but it certainly does simplify your code, and this is what is 
desired in 99% of the cases.  Can you give me an example of where you'd 
want to process data without knowing the format in advance?  What would 
you do with the results in that case?

But, it should be doable.  You can do something like:

if YAJL_IS_OBJECT(docNode);
   dow YAJL_OBJECT_LOOP(docnode: i: key: val);
     // do something (but what?) with the key and value.
   enddo
endif

likewise, you'd have to interrogate each subnode to determine if they 
are objects, arrays, or just straight values.  This could be done 
recursively...  but where I struggle is not with calling YAJL, but 
rather what you do with the results.

My experience with both JSON and XML is that you typically know the 
format in advance, and you code a data structure in RPG (or some similar 
structure like record formats in a PF) that matches the format of the 
file, so you do indeed know the format in advance, and you use something 
like XML-INTO or XML-SAX to load them with XML.  The same thing is 
available here with YAJL's tree routines (similar to XML-INTO in a way, 
though since it's not built into the compiler it can't get the names 
from the DS definition) or YAJL's stream-oriented routines (similar to 
XML-SAX)

Do you have situations where you parse documents without any knowledge 
of their format in advance?  How does that work?


On 6/1/2015 12:19 PM, Nathan Andelin wrote:
> Following are a few code snippets from one of Scott Klement's presentations
> on YAJL:
>
> docNode = yajl_stmf_load_tree( '/tmp/example.json' : errMsg );
>
> Without additional documentation or reviewing the code, it's not clear what
> yajl_stmf_load_tree() may be doing doing. Is it really parsing the stream
> file? Or is it just returning a pointer to the first "node" in the tree?
>
> The following appears to be parsing, but the syntax affirms that the
> programmer must know the layout of the file beforehand - that it contains
> an array of objects which contains a set of name-value pairs.
>
> list = YAJL_object_find(docNode: 'list');
>
> i = 0;
>
> dow YAJL_ARRAY_LOOP( list: i: node );
>    j = 0;
>    dow YAJL_OBJECT_LOOP( node: j: key: val);
>      exsr load_subfield;
>    enddo;
> enddo;