How to access subelements in Json object?

Getting Started
1

Hello

I was able to convert a JSON string into a dictionary. With simple structure like I can get each element value by .Value, so np…

In the end I want/need a more complex structure like:

[code]Var jsonText As String = “{”“town”":{ ““City””:"“Boston”","“Team”":"“Red Sox”"} }

Var mydict As Dictionary
mydict = ParseJSON(jsonText)
[/code]

Target: I simply want to get value of f.e. element “Team” (-> “Red Sox”)

The problem: All my tries leads to an error message or jumps into the debug mode. Using Json in Javascript is a nobrainer as you use the dot-notation. I don’t understand why this is such a problem (even if possible) in Xojo. I couldn’t find any example showing JSON access.

These examples do not work:

[code]// Direct way
MessageBox ( mydict.Value(“City”) )

// Through hiearchy
MessageBox ( mydict.Value(“town”).Value(“City”) )

// Dot notation
MessageBox ( mydict.town.Value(“City”) )[/code]

So general question: How (if) can I access sub-elements in a JSON object?

2 
dim sub as Dictionary = mydict.Value( "town" )
MessageBox sub.Value( "City" )
3

Woooot, fast and correct answer, you rock, thank you! I’m glad to have a solution. I’m not so happy I have to do it that way, but ok…

I recognised two problems: “sub” is a keyword, can’t be used as variable and MessageBox wants brackets.

For others who have the same problem, here two complete working samples with one and two hierarchies:

[code]// Sample for JSON acces with one hierarchy
Var jsonText As String = “{”“City”":"“Boston”","“Team”":"“Red Sox”"}"

Var mydict As Dictionary
mydict = ParseJSON(jsonText)

MessageBox ( mydict.Value(“City”) )[/code]

[code]// Sample for JSON acces with two hierarchies
Var jsonText As String = “{”“Town”":{ ““City””:"“Boston”","“Team”":"“Red Sox”"} }"

Var mydict As Dictionary
mydict = ParseJSON(jsonText)

Var mydictsub As Dictionary = mydict.Value( “Town” )
MessageBox ( mydictsub.Value(“City”) )[/code]

4

Yeah, I didn’t test, just wanted to give you an idea of how to do it.

5

All good, I thought so and I could get the point out of your code sample!

6

Dot notation like in Javascript does not xist in Xojo’s implementation of JSON
Not that it couldnt - it just doesnt
They could add runtime dot notation using operator_lookup
But that doesnt help at compile time :frowning:

7

@Norman Palardy Agree, otherwise I would have found it in the documentation. I’m aware that Xojo demands strong data typing and therefore the “simple” dot-notation does not fit in that concept. Thanks for your explanation!

8

dot notation doesnt mean strong or weak typing at all

Xojo’s JSON simp[ly doent use one of the built in language features to make it possible
And IF they did you would not know the dot notation was in error until runtime
http://documentation.xojo.com/api/math/operator_lookup.html

9

its because value return a variant and not a dictionary.
and because it not know the class it say .Value does not exists.
but you can cast/convert the return into a Dictionary

[code]Var jsonText As String = “{‘town’:{ ‘City’:‘Boston’,‘Team’:‘Red Sox’} }”
jsonText = jsonText.ReplaceAll("’",&u22)

Var mydict As Dictionary
mydict = ParseJSON(jsonText)

MessageBox ( Dictionary(mydict.Value(“town”)).Value(“City”) )[/code]

i think extends would help in your case.
documentation.xojo.com/api/language/extends.html

in a modul

[code]Public Function ValueDictionary(Extends obj As Dictionary, name As String) as Dictionary

Return Dictionary(obj.Value(name))

End Function
[/code]

example to use

MessageBox ( mydict.ValueDictionary("town").Value("City") )