Managing JSON Array format in MQL4 script - json

Question

I would need to get data from inside a JSON Array.
I use a call to WebRequest() function to get an order list from my db, thru a nodejs(api) and then I got the following JSON-data format e.g:
[{"orderid": 123556,
"ordertype": 0,
"ordercurrency": "EURUSD",
"orderdt": "2016-12-03 03:00:00"
},
{"orderid": 123457,
"ordertype": 0,
"ordercurrency": "GBPUSD",
"orderdt": "2016-12-03 03:15:00"
}
]
Any idea how to transform it to a normal array in order to manage data?
Thank you.
/Koul

Answer 1

JSON Serialization and Deserialization library works pretty well.
You can include it and finish your task within a minute or get an inspiration from its code.
https://www.mql5.com/en/code/13663
https://www.mql5.com/en/forum/65320
Let's assume you have the JSON data you pasted in a string variable named data.
#include <JAson.mqh>
// Object
CJAVal json;
// Load in and deserialize the data
json.Deserialize(data);
// Try to access the data elements
Alert(json["orderid"].ToInt());
Alert(json["ordercurrency"].ToStr());

Answer 2

How?Easy:
JSON-format is a "string-ified" representation of data-elements, put into a common container, be it a uchar[] or a string on the MQL4 side.
So, let's create a JSON-parser, coherent with the subset of the standard JSON-format syntax rules.
1) Search for all db-output "row"-s ( encapsulated in {...} )
2) Decode all db-output "column"-s ( encoded in ( known ) "KEY":VALUE pairs )
3) Store decoded values into any kind of target representation,
int orderIdNoARRAY[];
int orderTypeARRAY[];
string orderCurrARRAY[];
string orderDateARRAY[];
int anArrayStackPTR = 0
...
orderIdNoARRAY[anArrayStackPTR] = aDecodedOrderID; // 123556
orderTypeARRAY[anArrayStackPTR] = aDecodedOrderTYPE; // 0
orderCurrARRAY[anArrayStackPTR] = aDecodedOrderCURR; // "EURUSD"
orderDateARRAY[anArrayStackPTR] = aDecodedOrderDATE; // "2016-12-03 03:00:00"
or
#define oID 0
#define oTYPE 1
#define oCCY 2
#define oDATE 3
string stringDataFromJSON[10000,4];
int anArrayStackPTR = 0
...
stringDataFromJSON[anArrayStackPTR,oID] = (string)aDecodedOrderID; // 123556
stringDataFromJSON[anArrayStackPTR,oTYPE] = (string)aDecodedOrderTYPE; // 0
stringDataFromJSON[anArrayStackPTR,oCCY] = (string)aDecodedOrderCURR; // "EURUSD"
stringDataFromJSON[anArrayStackPTR,oDATE] = (string)aDecodedOrderDATE; // "2016-12-03 03:00:00"
or
struct aDB_RECORD{
int aDB_oID;
int aDB_oTYPE;
string aDB_oCCY;
string aDB_oDATE;
};
aDB_RECORD anArrayOfSTRUCTs[];
int anArrayStackPTR = 0
...
anArrayOfSTRUCTs[anArrayStackPTR].aDB_oID = aDecodedOrderID; // 123556
anArrayOfSTRUCTs[anArrayStackPTR].aDB_oTYPE = aDecodedOrderTYPE; // 0
anArrayOfSTRUCTs[anArrayStackPTR].aDB_oCCY = aDecodedOrderCCY; // "EURUSD"
anArrayOfSTRUCTs[anArrayStackPTR].aDB_oDATE = aDecodedOrderDATE; // "2016-12-03 03:00:00"
Yes, it is that easy!

Answer 3

Yes, JAson - JSON Serialization and Deserialization library works is good popular library:
https://www.mql5.com/en/code/13663
https://www.mql5.com/en/forum/65320
I wrote documentation with more details (different from https://www.mql5.com/en/code/13663) and added unit tests:
https://github.com/vivazzi/JAson.
It may be useful for you.

Answer 4

#property copyright "Copyright 2023, MetaQuotes Ltd."
#property link "https://www.mql5.com"
#property version "1.00"
#include <JAson.mqh>
int OnInit()
{
CJAVal data;
string aCookieHOLDER = NULL,
aHttpHEADERs;
char postBYTEs[],
replBYTEs[];
int aRetCODE;
string aTargetURL ="https://apitester.ir/api/Categories";
/* to enable access to the URL-> pointed server,
you should append "https://api.myjson.com/bins/56z28"
to the list of allowed URLs in
( Main Menu -> Tools -> Options, tab "Expert Advisors" ):
*/
ResetLastError();
int aTIMEOUT = 5000;
aRetCODE = WebRequest("GET",
aTargetURL,
aCookieHOLDER,
NULL,
aTIMEOUT,
postBYTEs,
0,
replBYTEs,
aHttpHEADERs
);
if ( aRetCODE == NULL )
{ Print( "Error in WebRequest(). Error code = ", GetLastError() );
}
else
{
string k=data.GetStr(replBYTEs,0,replBYTEs.Size());
data.Deserialize(k,0);
Comment(data.m_e[0].m_e[1].m_sv);
}
return(INIT_SUCCEEDED);
}
//after Deserialize you access any of row in json with m_e[0 to total size of objects] and access to any items of object with m_e[0 to count of keys]