MAXSTRING usually indicates that you're exceeding the maximum possible length of a string somewhere. Are you sure it's a problem with the %Stream.GlobalCharacter, and not a different string variable in your program? Global character streams shouldn't have that problem.

You can see what the maximum length of a string is on your system by opening a terminal and running:

write $SYSTEM.SYS.MaxLocalLength()

I've had some time to try this now. Here are steps that worked for me:

set myrequest = ##class(%Net.HttpRequest).%New()
set myrequest.Server = "<server ip or domain here>"
set myrequest.Port = "<server port here if it isn't 80>"
set myrequest.Location = "</path/to/rest>"
do myrequest.EntityBody.Write("<your json here>")
do myrequest.Post()
set mydata = myrequest.HttpResponse.Data.Read()

At that point, the data returned in the response should be in mydata.

Depending on your specific API, you made need to take additional steps for authentication, and you may need to use myrequest.Get() or myrequest.Put() instead of myrequest.Post().

If you need to set parameters, you use the SetParam method of the HttpRequest. For example, if you're using the very most basic way to authenticate to a Cache instance, you do that by specifying a CacheUserName and a CachePassword as parameters as follows any time before your post/put/get:

do myrequest.SetParam("CacheUserName","<your username here>")
do myrequest.SetParam("CachePassword","<your password here>")

Somewhere in your button tag, you have onselect= something. Buttons don't have an onselect, but even if they did, I'm guessing that's not the event you actually want. onselect happens when a user highlights text within a control, like in a text input.

If you're trying to set what happens when the user clicks the button, that's onclick.

If you're trying to set what happens when the user selects the button but doesn't click it (say by pressing tab until the button is highlighted) that's onfocus.

I think you're looking for the %ArrayOfObjects class for this one. You'd create your objects with all of their value, ID, and type properties, then you'd create the array:

set array = ##class(%ArrayOfObjects).%New()

Then you set values of the array using the SetAt method:

do array.SetAt(downobject,"down")

Then to access a particular value, you use the GetAt method, then dot syntax to access the object's properties:

set myid = array.GetAt("down").id

Here's the %ArrayOfObjects class documentation.

Try replacing your while loop with this:

//set RET to a blank string to start to avoid issues with the first concatenation inside the loop
s RET = ""
while res.Next()
    {
     //Append a ~ and the value to RET
     s RET = RET_"~"_ res.GetData(2)
}
//The way we did this, RET will now start with a ~, which we'll want to remove
//This will look at RET, replace tildes with nothing, starting at the beginning, and only making one replacement
$REPLACE(RET,"~","",1,1)

//having done that, RET should now be, "description 1~description 2"

If you want to be able to call that method without first creating an instance of your class, you need to define the method as a Class Method, not just a Method. Add "Class" before Method on that function definition and recompile your class, and it will probably work.

Otherwise, like Marc said, you'll have to instantiate the class then call the method on that instance.

I think you can accomplish this is $LISTFIND. It searches a list for a value, and returns its position in the list. If the item isn't found in the list, it will return a 0. For example, if you've got a list of colors called colorlist you'd use "where $LISTFIND(colorlist,'blue') > 0" in your SQL predicate to only include rows that have "blue" in their list. If the list contained "red", "blue", and "green" in that order, the $LISTFIND would return a 2. If the list contained "orange", "yellow", "taupe", the $LISTFIND would return a 0 because "blue" wasn't found and that row would be excluded.

Neither of the previous replies did exactly what I wanted to do, but action set to "New Window", filled the URL box with the URL but putting $$$VALUELIST where I needed that value to be, and set the "Active When" drop down to "1 Listing Item Selected". I set the Type to "Button" and gave it a label.

Now when you view listings in this dashboard and select one, you can click that button at the top to navigate where you need to go. That works for my purposes!