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

I have a db2 table with a column that contains JSON...
how do I describe my "from" when it is a column within a table I am

I have a db2 table with a column that contains JSON...
how do I describe my "from" when it is a column within a table I am
referencing (to extract the json data)?



On Wed, Aug 16, 2017 at 8:43 AM, Charles Wilt <charles.wilt@xxxxxxxxx>
wrote:

Oh 7.2 got JSON_TABLE() in October 2016 also...

Charles

On Wed, Aug 16, 2017 at 7:42 AM, Charles Wilt <charles.wilt@xxxxxxxxx>
wrote:

RPG's not the right choice for this...

Unless you happen to be on 7.3 and can build a dynamic SQL statement

that

uses the JSON_TABLE() function.

I think PHP or Python would be able to do this pretty easy.

Charles

On Wed, Aug 16, 2017 at 5:09 AM, Maria Lucia Stoppa <mlstoppa@xxxxxxxxx

wrote:

Henrik, it doesn't seem to me it works the way I need it to work,

because

in your specification "%addr(cust)" cust is the name of the final

variable

that must be loaded with content retrieved from json, while in my case

it

is exactly what I don't know; instead I have a variable namevar which
contains "cust" read from data structure.

2017-08-15 13:18 GMT+02:00 Maria Lucia Stoppa <mlstoppa@xxxxxxxxx>:

I see. Ok I will try it. Thank you
Il 14/Ago/2017 14:05, "Henrik Rützou" <hr@xxxxxxxxxxxx> ha scritto:

This is where it gets a little tricky.

Let assume you have a name field frmpos 11 topos 41 in the DS named

cust

the storage
address for name will start at addr = %addr(cust)+frmpos-1

Then you can move the JSON data byte to byte into the DS in a

for-loop.

The
reason that
you have to move it byte for byte and not as a block is that you may
overwrite other data if
the block is bigger than the result field.

This is rather simple for a alpha field but rather complicated for

numeric

and even packed
numeric fields.

On Mon, Aug 14, 2017 at 1:39 PM, Maria Lucia Stoppa <

mlstoppa@xxxxxxxxx>

wrote:

Sure, there is something I am missing.

I make use of API often, so in my case at a certain point there

might

be an

RPG variable rfNAME evaluated through API (or at least other two *

methods

I can think of) whose content is "NAME" and the JSON current node

name

is

"NAME" whose paired value is "Maria Lucia"; then comparing rfNAME

and

JSON

nodename I finally know I have found the right JSON node for a

variable

belonging to my data structure: how would you write an RPG

specification

which assign "Maria Lucia" to RPG variable NAME?

2017-08-14 10:35 GMT+02:00 Henrik Rützou <hr@xxxxxxxxxxxx>:

Here is what you need and it will give you alle the info you

need:

https://www.ibm.com/support/knowledgecenter/en/ssw_i5_54/

apis/quslfld.htm

On Mon, Aug 14, 2017 at 9:47 AM, Maria Lucia Stoppa <

mlstoppa@xxxxxxxxx>

wrote:

If the variable that contains the name is untied to its

pointer

how

can

it

be used to load data in the right memory position?
Il 14/Ago/2017 09:32, "Henrik Rützou" <hr@xxxxxxxxxxxx> ha

scritto:

Maria,

if you define the datasctructure externally there are API's

that

can

read

the field names in the DS
within your program and then you can use JSON-"find".

There may however be a problem since JSON names are case

sensitive

and

DS

names probably
are in upper case.


On Mon, Aug 14, 2017 at 9:12 AM, Maria Lucia Stoppa <

mlstoppa@xxxxxxxxx>

wrote:

Hi everybody

Thank you all for this interesting thread. Just let me

sum up

all I

read

in

it.

I would leave Javascript outside this discussion, because

I

have to

do

this

job in pure RPG ILE without the help of WDSC or other

develop

environment.

Anyway, JSON format being pretty much similar to

Javascript

object

description is done on purpose as it makes data

immediately

available

in

a

Javascript object just after being read.

I think all of you got the point of my request, which is

to

programmatic

read JSON data to be loaded into a data structure; anyway,

from

all

your

answers it seems impossible to match a JSON pair

name/value

with a

DS

variable/value and that leads to build a couple of

programs:

a

generator

code which knowing the data structure to be loaded can

write

appropriate

specifications which in turn know what to read.

Because the obstacle here is how to make a JSON node

identifying

itself

in

a given data structure, as Jon clearly pointed out.

In my case, types and lengths of variables against those

of

JSON

values

are

not an issue, because they must match otherwise an error

should

arise.

Let me try to reverse the approach: my routine starts

looping

through

the

data structure definition, let's say by reading DS D

specifications

or

whatever is needed as this is a different topic, then the

generic

routine

can look for a specific information into the JSON. But

how?

Given

my

ignorance, I guess variables' names are converted into

pointers

at

compile

time, but is there a way to reverse the process so that to

obtain a

variable which contains the name of a variable given a

pointer?

2017-08-14 3:55 GMT+02:00 Jon Paris <

jon.paris@xxxxxxxxxxxxxx>:

You missed my point Brad - which was that

YAJL_OBJECT_LOOP

will

loop

through anything. The rest of it was just showing how

the

generic

object

can be compared to find its identity.

But I agree in as much as one always needs to know

something

in a

business

processing environment. Unless you are simply writing a

utility

to

report

(for example) on what it finds.


Jon Paris

www.partner400.com
www.SystemiDeveloper.com

On Aug 13, 2017, at 12:22 PM, Bradley Stone <

bvstone@xxxxxxxxx

wrote:

On Sun, Aug 13, 2017 at 1:53 PM, Jon Paris <

jon.paris@xxxxxxxxxxxxxx

wrote:

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.

How is knowing the names, data types and container not

knowing

the

structure?

You know you're in a customer array that contains at

least a

numeric

ID and character name. I'd say that's at least

knowing

the

structure

at least partially, if not wholly.

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.

Bradley V. Stone
www.bvstools.com
MAILTOOL Benefit #2: The ability to specify a "From"

and/or

"Reply

To"

email address!
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