VBA JSON - Parse Multiple Values - json

Question

I'm having trouble using the JSON-VBA converter with a multiple values key.
I have the normal recursion routines written to navigate JSON trees but here's an example of a simple JSON parse which I can't seem to get to work.
See this for the VBA-JSON converter software, which is terrific and fast.
Environment: Windows 7 / Access 2016 / Private LAN (no Internet)
Here's the code:
Option Compare Database
Option Explicit
Sub testparse()
Dim js As String, i As Long, jo As Object, item As Variant
Dim keys(), vals()
' fails on this string
js = "{ !Category!: !Famous Pets!," & _
"!code!: [!a!,!b!,!c!] }" ' string with multiple values
' with the following string, this works
js = "{ !Category!: !Famous Pets!," & _
" !code!: !singlecodevalue! }"
js = Replace(js, "!", Chr(34)) ' replace ! with quotes
Debug.Print " js = " & js
Set jo = JsonConverter.ParseJson(js) ' returns object with json elements
i = 0
ReDim keys(1 To jo.Count)
ReDim vals(1 To jo.Count)
Debug.Print " Number keys found at top level " & jo.Count
For Each item In jo
i = i + 1
keys(i) = item
vals(i) = jo(item)
Next item
For i = 1 To jo.Count
Debug.Print "key " & keys(i) & " = " & vals(i)
Next i
End Sub

Answer 1

For each item you encounter when running through a JSON object, you have to determine what you're dealing with -- especially if you don't know ahead of time how many items in an array! It gets even trickier if you have a compound JSON structure with collections inside arrays and such.
The bottom line is that you have to check each item you pull out of the JSON object and figure out what it is before accessing it. The top level of a JSON object (assuming the use of JsonConverter) will always be a Dictionary. So you can count on looping through the keys of the top level dictionary:
Dim json As Dictionary
Set json = JsonConverter.ParseJson(someJsonString)
Dim topLevelKey As String
For Each topLevelKey In json
Dim item As Variant
Debug.Print topLevelKey & " = " & item
Next topLevelKey
The problem with this is the item is not always a simple string. It can be a value (String), an array (Collection), or a group (Dictionary). See this answer as a good reference.
Basically, this means you have to check each item before you use it. So you can check it like this:
Select Case TypeName(item)
Case "Collection"
'--- loop through the item as a Collection
Case "Dictionary"
'--- loop through the item as a Dictionary
Case Else
'--- the item is a value of some type (String, Boolean, etc)
End Select
In my example here, I created a sub called ParseItem that checks each of the items in this manner. Reworking your original code into the example below:
Option Explicit
Sub testparse()
Dim js As String, i As Long, jo As Object, item As Variant
Dim keys(), vals()
' fails on this string
js = "{ !Category!: !Famous Pets!," & _
"!code!: [!a!,!b!,!c!] }" ' string with multiple values
' with the following string, this works
' js = "{ !Category!: !Famous Pets!," & _
' " !code!: !singlecodevalue! }"
'--- compound example
' js = "{ !Category!: !Famous Pets!,!code!: [!a!,!b!,{!c! : { !c1! : !1!, !c2!:!2!}}] }"
js = Replace(js, "!", Chr(34)) ' replace ! with quotes
Debug.Print "----------------------"
Debug.Print "js = " & js
Set jo = JsonConverter.ParseJson(js) ' returns object with json elements
ParseDictionary 1, "root", jo
End Sub
Private Sub ParseCollection(ByVal level As Long, _
ByVal key As String, _
ByRef jsonCollection As Variant)
Dim item As Variant
For Each item In jsonCollection
ParseItem level, key, item
Next item
End Sub
Private Sub ParseDictionary(ByVal level As Long, _
ByVal key As String, _
ByRef jsonDictionary As Variant)
Dim dictKey As Variant
For Each dictKey In jsonDictionary
ParseItem level, dictKey, jsonDictionary(dictKey)
Next dictKey
End Sub
Private Sub ParseItem(ByVal level As Long, _
ByVal key As String, _
ByRef item As Variant)
Select Case TypeName(item)
Case "Collection"
Debug.Print Format(level + 1, "00 ") & key & " (collection)"
ParseCollection (level + 1), key, item
Case "Dictionary"
Debug.Print Format(level + 1, "00 ") & key & " (dictionary)"
ParseDictionary (level + 1), key, item
Case Else
Debug.Print Format(level, "00 ") & key & " = " & item
End Select
End Sub