It is better to check this with your license, as it is likely that some of its options, such as Web Add-on, may affect this (see $SYSTEM.License.PublicWebAppUser).

Hi Robert.

I also got carried away with this question and found two more ways to use indexes for a list of serial objects, and you can explicitly specify specific fields in the query, rather than $list (%Value,3).

The speed may be not always the best, but I did the best I could. I tested on Caché (perhaps something has been improved in IRIS in this regard?)

If you're interested, I can share it.

See Working with Streams

Topicstarter indicated Caché 2018.1, which is no longer being developed so not may change in the future (not counting security patches)

Unfortunately, %INLIST does not use indexes (at least it was in Caché, I do not know how it is now in IRIS), which I made a note about in my article.

$LISTFIND certainly does its job well, but there is a better solution.

As the data grows, the search speed will drop, since this solution does not use indexes in any way.
Therefore, the best solution is to use the predicate FOR SOME %ELEMENT.

For more details with examples, see one of my articles: SQL Performance Resources (item k. Indexing of non-atomic attributes)

The interactive tutorials with exercises built into the documentation helped me a lot in my time:

• Caché Tutorial Topics Map
• Caché Tutorials

Also included was a database "SAMPLES" (code and data) with examples for every taste. I often used it for performance testing.

In addition, in the <cachesys>\dev\ folder there were numerous demos with source code for various programming languages and connection technologies (С++, C#, Java, PHP, Python, ODBC, JDBC, ADO.NET, ActiveX, XEP, etc.):

\dev\tutorials\
\dev\tutorials\csp
\dev\tutorials\java
\dev\tutorials\mv
\dev\tutorials\pojo
\dev\tutorials\security
\dev\tutorials\UnitTestEx
\dev\tutorials\webservices
\dev\tutorials\zen

\dev\Cache\
\dev\Cache\callin
\dev\Cache\callout
\dev\Cache\cctrlcpp
\dev\Cache\cctrlvb
\dev\Cache\ctrldemo
\dev\Cache\HAcluster

\dev\odbc\samples\
\dev\odbc\samples\php
\dev\odbc\samples\select
\dev\odbc\samples\sqlgateway

\dev\python\
\dev\python\samples
\dev\python\samples3

\dev\cdirect
\dev\cpp\samples
\dev\dblib\samples
\dev\dotnet\samples
\dev\java\samples
\dev\mv\samples
\dev\node.js\samples
\dev\perl\samples

And now it's right?

N<=9 (59 chr)

N>9 (62 chr)

Who is shorter? ;)

Sorry, I didn't notice. Updated

Examining an XML Subtree

  try{

    $$$ThrowOnError(##class(%XML.XPATH.Document).CreateFromString("<a><b><c>some content</c></b></a>", .doc))
    $$$ThrowOnError(doc.EvaluateExpression("/a", "b", .field))
    #dim obj As %XML.XPATH.DOMResult = field.GetAt(1)
    
    while obj.Read() {
      if obj.HasValue {
        write obj.Path,": ",obj.Value,!
      }
    }
    
  }catch(ex){
    write "Error ", ex.DisplayString(),!
  }

Result:
b\c: some content

There is another way.
If you want any empty strings to always be treated as null/"" instead of "/$c(0), then there is an documented setting (within the scope of namespace), namely:

^%SYS("sql","sys","namespace",<YOUR_NAMESPACE>,"empty string")

Here is a small example:

Class dc.test Extends %Persistent
{

Property i As %Integer;

Property str As %String;

/// do ##class(dc.test).Test()
ClassMethod Test()
{
 do ..%KillExtent()
 
 try{
  
  do $system.SQL.Purge()
  set ^%SYS("sql","sys","namespace",$namespace,"empty string")=$c(0)

  ; '' -> $c(0)
  do ##class(%SQL.Statement).%ExecDirect(,"insert into dc.test(i,str) values(1,'')")
  
  ; null -> ""
  do ##class(%SQL.Statement).%ExecDirect(,"insert into dc.test(i,str) values(2,null)")
  
  do $system.SQL.Purge()
  set ^%SYS("sql","sys","namespace",$namespace,"empty string")=""

  ; '' -> ""
  do ##class(%SQL.Statement).%ExecDirect(,"insert into dc.test(i,str) values(11,'')")
  
  ; null -> ""
  do ##class(%SQL.Statement).%ExecDirect(,"insert into dc.test(i,str) values(22,null)")

  zwrite ^dc.testD
  kill ^%SYS("sql","sys","namespace",$namespace,"empty string")
 }
 catch(ex){
  write ex.DisplayString(),!
 }
}

}

USER>do ##class(dc.test).Test()
^dc.testD=4
^dc.testD(1)=$lb("",1,$c(0))
^dc.testD(2)=$lb("",2,"")
^dc.testD(3)=$lb("",11,"")
^dc.testD(4)=$lb("",22,"")

Another option just for the fun:

Include %SYS.PTools.Stats

Class dc.test [ Abstract ]
{

ClassMethod setValue(args...) As %Status
{
  quit:args<2 $$$ERROR($$$DataMissing)

  $$$convertArrayToList(args,list)
  quit:$listlength(list)'=args $$$ERROR($$$RequiredArgumentMissing)
  
  set $list(list,*,*)="",
         var=##class(%Utility).FormatString(list),
         $extract(var,1,3)=$name(%sessionData), ##; or $name(%session.Data)
         @var=args(args)
  quit $$$OK
}

/// do ##class(dc.test).Test()
ClassMethod Test()
{
  new %sessionData

  try{

    do $system.OBJ.DisplayError(..setValue("key1", "val1")),
          $system.OBJ.DisplayError(..setValue("key1", "key2", "key3", "key4", "val2")),
          $system.OBJ.DisplayError(..setValue("key1", "key2", , "key4", "val3")),
          $system.OBJ.DisplayError(..setValue())
    
    write !
    zwrite %sessionData
  }
  catch(ex){
    write ex.DisplayString(),!
  }
}

}