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Robert Cemper · Jul 8, 2020

IRIS has added a new parameter in 25 Data Classes:   
Parameter JSONTYPE = ...
I'll see the impact  as soon as I find free time

%Library.Binary.cls(JSONTYPE): Parameter JSONTYPE
%Library.Boolean.cls(JSONTYPE): Parameter JSONTYPE
%Library.Currency.cls(JSONTYPE): Parameter JSONTYPE
%Library.Date.cls(JSONTYPE): Parameter JSONTYPE
%Library.Decimal.cls(JSONTYPE): Parameter JSONTYPE
%Library.Double.cls(JSONTYPE): Parameter JSONTYPE
%Library.EnumString.cls(JSONTYPE): Parameter JSONTYPE
%Library.FilemanDate.cls(JSONTYPE): Parameter JSONTYPE
%Library.FilemanTime.cls(JSONTYPE): Parameter JSONTYPE
%Library.FilemanTimeStamp.cls(JSONTYPE): Parameter JSONTYPE
%Library.FilemanTimeStampUTC.cls(JSONTYPE): Parameter JSONTYPE
%Library.FilemanYear.cls(JSONTYPE): Parameter JSONTYPE
%Library.Float.cls(JSONTYPE): Parameter JSONTYPE
%Library.InformixTimeStamp.cls(JSONTYPE): Parameter JSONTYPE
%Library.Integer.cls(JSONTYPE): Parameter JSONTYPE
%Library.List.cls(JSONTYPE): Parameter JSONTYPE
%Library.ListOfBinary.cls(JSONTYPE): Parameter JSONTYPE
%Library.Name.cls(JSONTYPE): Parameter JSONTYPE
%Library.Numeric.cls(JSONTYPE): Parameter JSONTYPE
%Library.PosixTime.cls(JSONTYPE): Parameter JSONTYPE
%Library.Status.cls(JSONTYPE): Parameter JSONTYPE
%Library.String.cls(JSONTYPE): Parameter JSONTYPE
%Library.StringTimeStamp.cls(JSONTYPE): Parameter JSONTYPE
%Library.Time.cls(JSONTYPE): Parameter JSONTYPE
%Library.TimeStamp.cls(JSONTYPE): Parameter JSONTYPE
Robert Cemper · Jul 8, 2020

With a small extension, you may get closer to your result.
What you expect is a JSON Array, but %JSONExport... works on data OBJECTS, not on data TYPES { same as XMLExport() }

So I have created a small wrapper object:

Class Test.javier Extends (%RegisteredObject, %JSON.Adaptor) 
{ Property wrap As Test.elementList(%JSONFIELDNAME = " "); }

extending Test.Main:

Class Test.Main Extends %RegisteredObject 
{ ClassMethod Run()  {
  Set elem = ##class(Test.element).%New()
  Set elemList = ##class(Test.elementList).%New()
  Do elemList.Insert(elem)
#; Do elemList.%JSONExportToString(.json)
#; Do ##class(%ZJSON.Formatter).%New().Format(json)
#;; extended
 set jav=##class(Test.javier).%New()
 set jav.wrap=elemList
 Do jav.%JSONExportToString(.json)
 set json=$e($p(json,":",2,*),1,*-1)  ;  a little bit dirty 
 Do ##class(%ZJSON.Formatter).%New().Format(json)
} }

And here we go:

SAMPLES>do ##class(Test.Main).Run()
[
    {
      "field1":"testField1",
      "field2":"testField2"
    }
]
SAMPLES>
Robert Cemper · Jul 8, 2020

Just to verify if this is a %JSON specific problem I added also %XML.Adaptor to the classes.
And there is a similar problem: %ListOfObjects seems to be the bad guy. 

Do elemList.%JSONExport()
      {"ElementType":"Test.element","Size":1}
Do elemList.XMLExport()
     <elementList><ElementType>Test.element</ElementType><Size>1</Size></elementList>
zw elemList
elemList=2@Test.elementList  ; <OREF>
+----------------- general information ---------------
|      oref value: 2
|      class name: Test.elementList
| reference count: 2
+----------------- attribute values ------------------
|            Data(1) = ""
|        ElementType = "Test.element"
|            Oref(1) = "1@Test.element"
|               Size = 1  <Set>
+-----------------------------------------------------
Robert Cemper · Jul 7, 2020

in your query, I  see "Timestamp"  and Timestamp

Check the status of SUPPORT_DELIMITED_IDENTIFIERS parameter

Next check the date type of your column named Timestamp.
easiest SELECT top 5 "Timestamp","Skillset"  FROM "dbo"."iSkillsetStat"  
 also try SELECT Timestamp,Skillset  FROM dbo.iSkillsetStat
without any quoted columns  

Robert Cemper · Jul 6, 2020

Just found an example:

Class Demo.Loan.BankUS Extends Ens.BusinessProcess [ ClassType = persistent, ProcedureBlock ]
{ /// 2 modes: Queue, InProc
Parameter INVOCATION = "Queue"; Property CreditRating As %Integer; Property PrimeRate As %Numeric; Method OnRequest(
    request As Demo.Loan.Msg.Application,
    Output response As Demo.Loan.Msg.Approval) As %Status
{
    Set $ZT="Trap",tSC=$$$OK
    Do {
        $$$TRACE("received application for "_request.Name)
        #;
        If $zcrc(request.Name,2)#5=0 {
            Set response = ##class(Demo.Loan.Msg.Approval).%New()
            Set response.BankName = "BankUS"
            Set response.IsApproved = 0
            $$$TRACE("application is denied because of bank holiday")
            Quit
        }
        #;
        Set tRequest = ##class(Demo.Loan.Msg.PrimeRateRequest).%New()
        Set tSC = ..SendRequestAsync("Demo.Loan.WebOperations",tRequest,1,"PrimeRate")
        #;
        Set tRequest = ##class(Demo.Loan.Msg.CreditRatingRequest).%New()
        Set tRequest.TaxID = request.TaxID
        Set tSC = ..SendRequestAsync("Demo.Loan.WebOperations",tRequest,1,"CreditRating")
        #;
        Set tSC = ..SetTimer("PT15S")
        #;
        Quit
    } While (0)
Exit
    Quit tSC
Trap
    Set $ZT="",tSC=$$$EnsSystemError Goto Exit
} /// Handle a 'Response'
Method OnResponse(
    request As Ens.Request,
    ByRef response As Ens.Response,
    callrequest As Ens.Request,
    callresponse As Ens.Response,
    pCompletionKey As %String) As %Status
{
    Set $ZT="Trap",tSC=$$$OK
    Do {
        If pCompletionKey="PrimeRate" {
            Set ..PrimeRate = callresponse.PrimeRate
        } Elseif pCompletionKey="CreditRating" {
            Set ..CreditRating = callresponse.CreditRating
        }
        Quit
    } While (0)
Exit
    Quit tSC
Trap
    Set $ZT="",tSC=$$$EnsSystemError Goto Exit
} Method OnComplete(
    request As Ens.Request,
    ByRef response As Ens.Response) As %Status
{
    Set $ZT="Trap",tSC=$$$OK
    Do {
        Set response = ##class(Demo.Loan.Msg.Approval).%New()
        Set response.BankName = "BankUS"
        Set tIsUsCitizen=($zcvt($tr(request.Nationality,"."),"u")="USA")||($zcvt($tr(request.Nationality,"."),"u")="US")
        If ('tIsUsCitizen)||(..CreditRating<50) {
            Set response.IsApproved = 0
            $$$TRACE("application is denied")
        } Else {
            Set response.IsApproved = 1
            Set response.InterestRate = ..PrimeRate+2+(5*(1-(..CreditRating/100)))
            $$$TRACE("application is approved for "_response.InterestRate_"%")
        }
        Quit
    } While (0)
Exit
    Quit tSC
Trap
    Set $ZT="",tSC=$$$EnsSystemError Goto Exit
}
Storage Default
{
 <Data name="BankUSDefaultData">
   <Subscript>"BankUS"</Subscript>
   <Value name="1">
      <Value>CreditRating</Value>
   </Value>
   <Value name="2">
      <Value>PrimeRate</Value>
   </Value>
 </Data>
 <DefaultData>BankUSDefaultData</DefaultData>
 <Type>%Library.CacheStorage</Type>
} }
 
Robert Cemper · Jul 6, 2020

#1)
- create a simple Business Process using the wizard
- compile it and see the resulting class and at least 4 related .int routines.
- then decide if you really want to do this all manually
the challenge is to properly use and service the methods you see in Ens.BusinessProcess

To make it easier you may install (or activate) the ENSDEMO namespace as an example (before IRIS. have no idea where it is gone)

#2)

you write.    ---transformation (written in DTL), but the code is manually written. ---

It might sufficient to put your code just into a CODE Block of a BP generated with the wizard.