Re: Parsing JSON data into a data structure without knowing variable's names

The real difference between XML and JSON is that object and arrays may not
have names so
it is often impossible to build an XPATH to a JSON object:

XML:
<orders>
<order>
<ordernumber>12345 ...

JSON (objects within an array has no name)
"orders" : [
{
"ordernumber" : 12345 ...

JSON (root has no name)
[
{
"ordernumber" : 12345 ...

In my own XML parser that works like XML-SAX I always know where I am
because
each element also has the XPATH

XPATH: /orders/order
Element: ordernumber
Value: 12345

In XML you can just use Joe Celko's "Tree Traversal Algorithm" to walk
through the XML.
It works with SQL and with RPGLE repetitive called procedures.

In JSON you cant even though it is rather simple to convert JSON to XML
using pseudo
element names where they are missing.

So it may be impossible to make a general routine that maps any JSON to a
predefined
datastructure - you simply need to know where you are in the JSON.

On Sun, Aug 13, 2017 at 9:37 PM, John Yeung <gallium.arsenide@xxxxxxxxx>
wrote:

On Sun, Aug 13, 2017 at 3:22 PM, Bradley Stone <bvstone@xxxxxxxxx> wrote:

As I said earlier I think code gen is the way to go - but the JSON

structure can be dynamically determined just as XML-SAX allows you to do
with XML.

Yes, that makes sense, but once you do the program "knows" the
structure and is built appropriately around thus said structure.

But which program are you talking about? I think Jon is talking about
at least two programs. One is a code generator, and it doesn't have
compile-time knowledge of the structure, but can determine it
dynamically. Then, it uses this knowledge to build code for a separate
program, which *does* know the structure at compile-time, by means of
this generated code.

This is also the approach espoused by Joe, and it's what I would do as
well, if I were doing it in RPG.

Maybe you are agreeing with all this, but I'm clarifying that one
program does NOT have foreknowledge of the structure, while the other
DOES. (Because it was imparted by the first program.)

John Y.
--
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