Sorry, I don't quite get you.

One used to say, if I don't understand something, then this something is either too complicated or very simple. So where belongs your case?

I'm not sure about what you mean with "unlimited amount of indexes"...

first, there is a limit of 255 for the parameters, this means you can have 

do ..setValue(key1,key2,...key254,value)

but you can't have 

 do ..setValue(key1,key2,...key254,key255,value)

second, if you meant to have many-many values (in sense of, we have to much data)

  do ..setValue(key1,value1)
  do ..setValue(key2,value2)
  // etc.

then, at some point you will reach the and of the available RAM (incl. swap/paging space.  Usually swap/paging space is much less then the space for the real data).

thirdly, if you meant variable number of indexes (in sense of variable number of parameters) then I can just refine Robert's solution to

ClassMethod setValue(params...) As %Status
{
   set base=$name(%session.Data)
   for i=1:1:params-1 { set base=$name(@base@(params(i)))
   set @base=params(params)
   quit 1
}

In case, you have both, variable number of indices and too much data then you could use a mix of the above with data placed in a temp file.

Somewhere, at the program start, let you point %sessionData to a temp file

   set %sessionData=$nam(^||SessionTemp)

and then consider this in the setValue method

ClassMethod setValue(params...) As %Status
{
   set bas=%sessionData
   ...
}

Of course, in your application, you have to change only those %session.Data(...) to  @%sessionData@(...)  which uses the "variable-big-data" part of %session.Data(). All other (the standard ones) stay unchanged.

Oh yes,  DATEADD(ms, ....) works, but

select  'Arrival Time' ... 

won't work. This gives the string constant of "Arrival Time"

Sorry, I didn't noticed the space char... maybe I need new glasses ;-)

But yes, if you have some unusual property names, then you need double-quotes ($char(34), he used $char(39))

I'm pretty sure, you intended to write

select COUNT (Arrival Time) FROM dbo.table where Arrival Time < DATEADD(ms, CONVERT(int,LEFT(1603173432000, 20)), '1970-01-01 00:00:00')

i.e. do not place propertynames under quote

By the way, I don't know, how many records you have in your table, but if you have thousands or millions of records, consider to compute constant things just one time!

DATEADD(ms, CONVERT(int,LEFT(1603173432000, 20)), '1970-01-01 00:00:00')

is a constant value, it's not neccessary to compute it for each record! Also, in this particular case, CONVERT() and LEFT() are also not needless, 1603173432000 is the value, and it is an integer.

To say it simply, you did this:

set x=123
set x=456

and just  see 456 but not 123!

What you (probably) want to do is:

set x(1)=123
set x(2)=456

I added one more "patient item" to your JSON and a simple test class

Class DC.PR1 Extends %RegisteredObject
{ 
ClassMethod GetDataFromTestStream() [ PublicList = (myGuid, myId, myForename, mySurname, myDOB, nokName, nokRelation, nokTel, nokEmail) ]
{
   set xData=##class(%Dictionary.CompiledXData).%OpenId(..%ClassName(1)_"||Test")
   try { set obj={}.%FromJSON(xData.Data) }
   catch e { set obj="",err=e.Name }
   if 'obj { 
      write "Error: ",err,!
      quit ""
   }  

   // Put all properties in the corresponding SUBSCRIPTED variable
   //
   for i=0:1:obj.%Size()-1 { // loop over patients (top array)
      set patient=obj.%Get(i).patient

      set myGuid(i)=patient.guid
      set myId(i)=patient.id
      set myForename(i)=patient.forename
      set mySurname(i)=patient.surname
      set myDOB(i)=patient.dateOfBirth

      for j=0:1:patient.NOK.%Size()-1 { // loop over NOKs of the i-th patient
         set nok=patient.NOK.%Get(j)

         set nokName(i,j)=nok.NOKname
         set nokRelation(i,j)=nok.NOKrelationship
         set nokTel(i,j)=nok.telephone
         set nokEmail(i,j)=nok.email

         // instead of storing each property, you could
         // process them hier...
      }
   }
} 

XData Test [ MimeType = application/json ]
{
[
  {
    "patient":
      {
        "guid":"12345",
        "id":12345,
        "forename":"Joe",
        "surname":"Bloggs",
        "dateOfBirth":"2002-12-10T00:00:00Z",
        "NOK":[
                {
                   "NOKname":"Alison Bloggs",
                   "NOKrelationship":"Wife",
                   "telephone":"02081234567",
                   "email":"alison@bloggs.com"
                },
                {
                   "NOKname":"Peter Bloggs",
                   "NOKrelationship":"Father",
                   "telephone":"02081234567",
                   "email":"Peter@bloggs.com"
                }
              ]
      }
  },
  
  {
    "patient":
      {
        "guid":"212345",
        "id":212345,
        "forename":"John",
        "surname":"Blue",
        "dateOfBirth":"2003-12-10T00:00:00Z",
        "NOK":[
                {
                   "NOKname":"Aline Blue",
                   "NOKrelationship":"Wife",
                   "telephone":"032081234567",
                   "email":"aline@blue.com"
                },
                {
                   "NOKname":"Peter Blue",
                   "NOKrelationship":"Father",
                   "telephone":"032081234567",
                   "email":"Peter@blue.com"
                }
              ]
      }
  }

]
} 

}

Try it in a terminal session:

do ##class(DC.PR1).GetDataFromTestStream()

zwrite

The output  should be:

myDOB(0)="2002-12-10T00:00:00Z"
myDOB(1)="2003-12-10T00:00:00Z"
myForename(0)="Joe"
myForename(1)="John"
myGuid(0)=12345
myGuid(1)=212345
myId(0)=12345
myId(1)=212345
mySurname(0)="Bloggs"
mySurname(1)="Blue"
nokEmail(0,0)="alison@bloggs.com"
nokEmail(0,1)="Peter@bloggs.com"
nokEmail(1,0)="aline@blue.com"
nokEmail(1,1)="Peter@blue.com"
nokName(0,0)="Alison Bloggs"
nokName(0,1)="Peter Bloggs"
nokName(1,0)="Aline Blue"
nokName(1,1)="Peter Blue"
nokRelation(0,0)="Wife"
nokRelation(0,1)="Father"
nokRelation(1,0)="Wife"
nokRelation(1,1)="Father"
nokTel(0,0)="02081234567"
nokTel(0,1)="02081234567"
nokTel(1,0)="032081234567"
nokTel(1,1)="032081234567"

And don't forget, you may have more then one "patient" item in your JSON, so either consume the data in the inner loop oder place them in a two-dimensional array.

HTH

$SYSTEM returns the (local) name of a machine (where Cache/IRIS is installed), a colon, and the instance name.
Sorry, my mistake.

FQDN is the fully qualified domain name for a specific computer, or host, on the internet.

$SYSTEM returns the (local) name of a machine (where Cache/IRIS is installed), a colon, and the actual namespace. Usually, Cache and IRIS are not exposed to internet.

So the question is, what you need, what you want to do?

Unfortunately no, because I have nothing to do with HealthShare, HL7 and all those healthy things. If you have any ObjectScript or Class problem, I am happy to help you.
 

see this

https://community.intersystems.com/post/how-create-index-inside-array

To make your (and others) life easier... here is a simple class to display a dynamic object (or dynamic array).

/// A general class for various helper functions
/// 
Class %zapi.utils Extends %RegisteredObject
{ /// Show an dynamic array or object
/// 
/// obj : the dynamic object (or array) you want to display
/// deep: max path depth, 0 (default) = display all
/// find: if given, (a part of) a property name
ClassMethod ShowObj(obj, deep = 0, find = "")
 {
   new %seen
   do ..shObj(obj,deep-1,find,"<obj>")
 }
ClassMethod shObj(obj, deep, find, path) [ Internal, Private ]
 {
   set path=path_"."
   set itr=obj.%GetIterator()
   while itr.%GetNext(.prop,.val) {
      set:obj.%IsA("%DynamicArray") prop="%Get("_prop_")"
      set prop=path_prop
      if $isobject(val) {
         if $data(%seen(+val)) { set val="same as --> "_%seen(+val)
         } else { set %seen(+val)=prop }
      }
      if $isobject(val),deep { do ..shObj(val,deep-1,find,prop)
      } else { write:prop[find prop,": ",val,! }
   }
 }
}

With our old pData,  use it as follows:

write pData 
[{"patient":{"guid":"12345","id":12345,"forename":"Joe","surname":"Bloggs","dateOfBirth":"2002-12-10T00:00:00Z"},"visit":[{"guid":45678,"date":"2020-01-10","reason":"other"},{"guid":45679,"date":"2020-01-11","reason":"routine"}],"
documentAttachments":[{"guid":"23432","id":152,"catergory":"notes"},{"guid":"23433","id":153,"catergory":"summary"}]}]

set obj={}.%FromJSON(pData)
do ##class(%zapi.utils).ShowObj(obj)

If you don't want to write each time a novel, you can create your own "show object" command too.
Insert the following line into %ZLANGC00 routine (if %ZLANG doesn't exists, create it):

ZSHO(obj, deep=0, find="") Public { do ##class(%zapi.utils).ShowObj(obj,deep,find) }

and Voila!, you got a short command to display dynamic objects

zsho obj              // display the whole object
zsho obj:2            // display up to  second nesting level
zsho obj::"visit"     // display all occurrences of property visit
zsho obj::"guid"      // display all occurrences of property guid

The outputs of the above commands are

USER>zsho obj
<obj>.%Get(0).patient.guid: 12345
<obj>.%Get(0).patient.id: 12345
<obj>.%Get(0).patient.forename: Joe
<obj>.%Get(0).patient.surname: Bloggs
<obj>.%Get(0).patient.dateOfBirth: 2002-12-10T00:00:00Z
<obj>.%Get(0).visit.%Get(0).guid: 45678
<obj>.%Get(0).visit.%Get(0).date: 2020-01-10
<obj>.%Get(0).visit.%Get(0).reason: other
<obj>.%Get(0).visit.%Get(1).guid: 45679
<obj>.%Get(0).visit.%Get(1).date: 2020-01-11
<obj>.%Get(0).visit.%Get(1).reason: routine
<obj>.%Get(0).documentAttachments.%Get(0).guid: 23432
<obj>.%Get(0).documentAttachments.%Get(0).id: 152
<obj>.%Get(0).documentAttachments.%Get(0).catergory: notes
<obj>.%Get(0).documentAttachments.%Get(1).guid: 23433
<obj>.%Get(0).documentAttachments.%Get(1).id: 153
<obj>.%Get(0).documentAttachments.%Get(1).catergory: summary

USER>zsho obj:2
<obj>.%Get(0).patient: 11@%Library.DynamicObject
<obj>.%Get(0).visit: 2@%Library.DynamicArray
<obj>.%Get(0).documentAttachments: 21@%Library.DynamicArray

USER>zsho obj::"visit"
<obj>.%Get(0).visit.%Get(0).guid: 45678
<obj>.%Get(0).visit.%Get(0).date: 2020-01-10
<obj>.%Get(0).visit.%Get(0).reason: other
<obj>.%Get(0).visit.%Get(1).guid: 45679
<obj>.%Get(0).visit.%Get(1).date: 2020-01-11
<obj>.%Get(0).visit.%Get(1).reason: routine

USER>zsho obj::"guid"
<obj>.%Get(0).patient.guid: 12345
<obj>.%Get(0).visit.%Get(0).guid: 45678
<obj>.%Get(0).visit.%Get(1).guid: 45679
<obj>.%Get(0).documentAttachments.%Get(0).guid: 23432
<obj>.%Get(0).documentAttachments.%Get(1).guid: 23433 

Have a nice day...