Re: Parsing JSON data into a data structure without knowing variable's names -- RPG400-L

Not necessary to know the structure Nathan as you can query what kind of node you are dealing with.

A straight object loop can also be used - for example:

Dow YAJL_OBJECT_LOOP( customerNode: i: key: node );
Select;
When key = 'ID';
customer(c).id = YAJL_GET_NUMBER( node );
When key = 'Name';
customer(c).name = YAJL_GET_STRING( node );

In this instance I only need certain fields and the names are known - but the YAJL_OBJECT_LOOP itself dd not require that I know the names or types of the objects.

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.

Jon Paris

www.partner400.com
www.SystemiDeveloper.com

On Aug 13, 2017, at 7:50 AM, Nathan Andelin <nandelin@xxxxxxxxx> wrote:

Henrik,

Maria was the one who first used the label "deep" to describe some of the
lesser-known procedure exports from YAJL. Your source-code example only
refers to the well-documented procedures, which require that the JSON
structure be known, before you can use them.

That program is "finding" a node reference by a name that must be known by
the programmer who is writing the code. Then looping through an array
within that node. The author of the program had to read the JSON himself in
order to write the code. That wouldn't work for generic utility.

Nathan.

On Sat, Aug 12, 2017 at 10:53 PM, Henrik Rützou <hr@xxxxxxxxxxxx> wrote:

Nathan,

it is not a "deep" function to make a reading loop i YAJL:

https://www.fieldexit.com/forum/display?threadid=197

On Sat, Aug 12, 2017 at 10:45 PM, Nathan Andelin <nandelin@xxxxxxxxx>
wrote:

Maria,

After reading this thread, I believe that I understand the gist of what
you're looking for. However, there is one part that I don't fully
understand, which you may be able to clarify.

My understanding is that you have web clients that send requests to an

IBM

i server, where the requests include JSON data (including hierarchically
structured data) that you need to parse, extract, and map JSON name-value
pairs to IBM i externally described data structure values, which may be
used as parameters for making IBM i program calls.

You appear to want to write a generic utility that automatically maps

JSON

name-values pairs to externally described data structure values, as an
alternative to the repetitive hand-coding required by the YAJL "find"
functions.

I think this can be done, but it appears to me that you may need some
tooling other than the YAJL "find" functions, because they require you to
have foreknowledge of the structure of the JSON that is received.

It may be possible for you to use some of the "deep" functions within

YAJL.

But the tests that I've run in that regard were not fruitful, except to
confirm that I was unable to get them to work.

It appears to me that rather than YAJL "find" functions, you'll need
something more like an EXPAT parser, or some other way to monitor the
parsing, so that you can implement generic functionality to map JSON
name-value pairs to external data structure values, including conversion

to

correct data types.

Nathan.

On Sat, Aug 12, 2017 at 11:19 AM, Maria Lucia Stoppa <mlstoppa@xxxxxxxxx

wrote:

Joe, FFD may not be necessary because I can use external D

specification

copied through /Copy option instead. I will do some test using pointers

and

deep YAJL available functions: maybe combining the two a new option may
arise.

Henrik, I am not sure about what you are meant to say. Looking at your

code

it seems to me that you are using a library different from YAJL where

your

function comes from. In this case a program generator will help by

adding

standardised code to my sources, included specific reference to

variable

names.
Il 12/Ago/2017 19:02, "Henrik Rützou" <hr@xxxxxxxxxxxx> ha scritto:

Since most JSON comes in from AJAX the only rule there is, is that

there

is

no rules
and most inexperienced programmers do think that they are smarter

than

standards
and main stream ways of doing things ;-)

On Sat, Aug 12, 2017 at 6:44 PM, Henrik Rützou <hr@xxxxxxxxxxxx>

wrote:

Okay, then take this input http://blablabla.pgm?parm1=
abcd&parm2=defg&json1={....}&json2={...}

Program generator?

On Sat, Aug 12, 2017 at 6:34 PM, Joe Pluta <

joepluta@xxxxxxxxxxxxxxxxx

wrote:

Yes, this seems like the most straightforward approach, Jon. Kind

of

like a web service generator that builds code based on a WSDL.

Sure,

THEORETICALLY you could map the data dynamically by looking at an
externally described data structure, and done properly you'd only

have

to

do it once, but the overhead of parsing an FFD every time could be
significant.

I like the generated adapter technique. A good balance between
flexibility and performance. As long as you can avoid the

temptation

to

tweak the generated code... :)

I concur with the others that in a language such as RPG this is

not

readily done. However, by constraining the problem space it can

be

done. I

wrote up this technique some 10 years ago

http://ibmsystemsmag.com/ibmi/

developer/rpg/how-flexible-are-your-calculations-/ <
http://ibmsystemsmag.com/ibmi/developer/rpg/how-flexible-ar
e-your-calculations-/> and this followup article which took it

one

step

further.
http://ibmsystemsmag.com/ibmi/developer/rpg/even-more-flexib
le-calculations/ <http://ibmsystemsmag.com/ibmi
/developer/rpg/even-more-flexible-calculations/> providing you

know

the

names of all fields involved, then this could work but I don't

think

t

is

the best solution.

Instead in your case I would suggest writing a simple code

generator

would be a more practical way of handling the multiple parameter

sets

that

you have. Rather than try and write a completely generic program

write

a

generic generator that spits out the RPG to do the JSON to DS

mapping

for

each of your DS. If the parameter set changes regen the code.

Nested structures would be harder to handle but by no means

impossible.

Jon Paris

www.partner400.com
www.SystemiDeveloper.com

On Aug 12, 2017, at 3:12 AM, Maria Lucia Stoppa <

mlstoppa@xxxxxxxxx>

wrote:

Hello,

I am new to this forum, but I have done some research related to

JSON

and
couldn't find anything similar to my issue.

I am working on a proof of concept to code new programs in order

to

parse
the only received parameter formed as a JSON object into a data
structure.

I explain it better: previously, all our programs received a

single

parameter defined as an external data structure, so as soon as

*entry

plist
operation code is executed the data structure and all the fields

in

it

were
filled in and made available for programs to use them (quite

common

solution). External data structure are defined as PF without

member

and

can
be used by any program that need to call the one which received

it

as

a

parameter to perform a specific function.

Now we are moving our ERP's graphic interface to web: it means

that

a

program call can be executed by a store procedure called either

by

web

applications or by RPG programs. To serve the purpose of having

a

quick

UI
response, parameters are passed coded in a JSON object and new

programs

have been coded to parse JSON input parameter field by field

using

SK's

JSON APIs (thanks!).

I am guessing whether I can expand and generalize this behavior

by

coding a
general routine which takes an external definition of JSON (even

nested)

structure and assigns each object's name found into JSON

parameter

to

its
corresponding variable name's value.

My nightmares are: firstly, today's external DS are one level

only

and I

can't figure out how to represent nested levels; secondly how to
dynamically associate the value of JSON pair to its

corresponding

variable's value according to its type.

One general idea might be to code some external D specifications

to

be

used
through /COPY option, which represent JSON structure in terms of
qualified
names and types, array included. Then JSON objects can be read

element

by
element but how can I address the right DS variable without

explicitly

write its name?

Can you suggest me some technique I haven't explored yet or any

other

way
to approach the problem?

Thank you

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