Example RPG to decode JSON from IFS using JSON_TABLE

This reads the JSON from the IFS – decodes it using JSON_TABLE and reports on time taken to perform decode.

In this case the JSON data is a simple layout that looks like this:

{"users":[{"userID":"@123","firstName":"Billy","lastName":"Bob","initials":"123","company":110,"division":30,"department":325,"secProfile":""},{"userID":"AAATEMP","firstName":"Albert","lastName":"Smith","initials":"AAA","company":110,"division":1,"department":1,"secProfile":""},{"userID":"AAATEST","firstName":"Andy","lastName":"Tester","initials":"AAA","company":110,"division":1,"department":530,"secProfile":"AAT"},{"userID":"AAA3","firstName":"Fred","lastName":"Blogs","initials":"AA3","company":110,"division":1,"department":1,"secProfile":"AAA"},{"userID":"AATEST","firstName":"AA","lastName":"TEST","initials":"AAT","company":110,"division":1,"department":1,"secProfile":""},{"userID":"ABB","firstName":"Abba","lastName":"Dancing Queen","initials":"","company":110,"division":1,"department":1,"secProfile":""},{"userID":"BINGBONG","firstName":"Bing","lastName":"Bong","initials":"BB","company":110,"division":2,"department":2,"secProfile":""},{"userID":"LITTENN","firstName":"Nick","lastName":"Litten","initials":"NJL","company":001,"division":1,"department":123,"secProfile":"Secret Squirrel"}]}

This JSON example contains the values:

USERID varchar(100);
FIRSTNAME varchar(100);
LASTNAME varchar(100);
INITIALS varchar(100);
COMPANY int(10);
DIVISION int(10);

Now lets read it and break it out into fields, which I am just storing in an array. You could write them to a file just as easily…


/TITLE JSON_TABLE Decode JSON using SQL - Proof of Concept

// Create as a Module and bind into ILE program
// JSNIFSSQL.sqlrpgle (fully /free)
// This demonstrates reading JSON data from an IFS file and then
// parsing that JSON using SQL JSON_TABLE functions.
// The JSON data is loaded into a data structure suitable
// for display from a program debugger.
// 07/17/2017 nick litten V1.0 Created
// 06/20/2021 nick litten V1.1 Removed unused variables for clarity

ctl-opt dftactgrp(*no) actgrp('NICKLITTEN')
datfmt(*ISO) decedit('0.')
copyright('| JSNIFSSQL V1.1 Use JSONTABLE to read IFS and parse JSON into array.');

// IFS file with JSON code that we will be reading and decoding
dcl-c ifsFilename const('/littenn/getwebjsn.json');

dcl-ds jsonFields qualified;
 USERID varchar(100);
 FIRSTNAME varchar(100);
 LASTNAME varchar(100);
 INITIALS varchar(100);
 COMPANY int(10);
 DIVISION int(10);
 DEPARTMENT int(10);

dcl-ds result qualified;
 success ind;
 errmsg varchar(500);
 jsonArray likeds(jsonFields) dim(9999);

// procedures and variables for IBM i *APIS to loads IFS into variable
dcl-pr open int(10) extproc('open');
 *n pointer value options(*string); // filename
 *n int(10) value; // openflags
 *n uns(10) value options(*nopass); // mode
 *n uns(10) value options(*nopass); // codepage

dcl-pr read int(10) extproc('read');
 *n int(10) value; // filehandle
 *n pointer value; // datareceived
 *n uns(10) value; // nbytes

dcl-pr close int(10) extproc('close');
 *n int(10) value; // filehandle

dcl-s Count int(10);
dcl-s Handle int(10);
dcl-s json sqltype(clob:16000000);
dcl-s ifsData char(16000000);
dcl-s ifsDataLen int(10);
dcl-s rc int(10);
dcl-s O_RDONLY int(10) inz(1);
dcl-s O_TEXTDATA int(10) inz(16777216);
dcl-s lastElem int(10);

dcl-ds ErrorCode;
BytesProv int(10) inz(0);
BytesAvail int(10) inz(0);

/Title [---------- MAINLINE ---------- ]

// Open the stream file
Handle = open(%trim(ifsFilename):O_RDONLY + O_TEXTDATA);

// Loop to read the stream file into variable "ifsData"
dou ifsDataLen<1;
Count += 1;
ifsDataLen = read(Handle:%addr(ifsData):%size(ifsData));

// Close the stream file
rc = close(Handle);

if ifsData <> *blanks;

// we have the IFS data loaded into variable(ifsData) so lets load
// that variable into the SQL(clob) and process it using the JSON_TABLE
// to break the JSON out into fields for processing. NOTE: we are not
// doing anything with those fields in this program because this is just
// a proof of concept
exec sql
 set option naming = *sys,
 commit = *none,
 usrprf = *user,
 dynusrprf = *user,
 datfmt = *iso,
 closqlcsr = *endmod;

exec sql
 declare c1 cursor for
 select *
 from json_table (:json, '$' // read the JSON data from a string
 columns (nested '$.users[*]' columns (userid varchar(100) path
 '$.userID', firstname varchar(100) path '$.firstName', lastname
 varchar(100) path '$.lastName', initials varchar(100) path
 '$.initials', company int path '$.company', division int path
 '$.division', department int path '$.department'))) as x;

exec sql
open c1;

exec sql
fetch next from c1
into :jsonfields;

dow sqlstt='00000' or %subst(sqlstt:1:2)='01';

lastelem += 1;

// Store Datastructure values in next element of 'return array'
result.jsonArray(lastelem) = jsonFields;

// here we could do something with each row of data ie: write to file
// or some other business logic.
exec sql
fetch next from c1
into :jsonfields;


exec sql
close c1;

result.success = *on;


// If unable to load JSON data from the IFS then tell the world
result.success = *off;
result.errmsg = 'Ouch! I couldnt read the IFS file';


*inlr = *on;

So what does this do?

  • Reads the JSON from the input IFS File
  • Decodes the JSON using JSON_TABLE and stores all the values in an array
{"email":"Email address invalid","url":"Website address invalid","required":"Required field missing"}