Advice about JSON conversions and reading outputs from Dynamic Objects

The above should work, so the question is, what is the content of pData. Do you can share a sample with us?

Also, you can write the above somewhat shorter too and you can access all the properties either via propertyname or via the %Get() method.

I assume, you have a string like this:

set pData="{""Name"":""Joe"", ""Age"":50}"

the you can do this

set object={}.%FromJSON(pData)
write object.Name // Joe
write object.%Get("Name") // Joe
write pData // {"Name":"Joe", "Age":50}

Check this post.

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...