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Robert Cemper · May 17, 2022

Status= 1 justteslls you tht the HTTP connection was processed OK.
Next you need to take a look into your response object.

set res=Httprequest.HttpResponse
in terminal then ZW res to see in the Status is 200 OK
otherwise what you see I  res.Data might be just an error page.
Which is also OK for HTTP but not for your content.

• property ReasonPhrase as %String;

This is the human readable reason that goes with the StatusCode.

• property StatusCode as %Integer;

The HTTP status code. This is useful to determine if the request was successful. Look in the rfc for HTTP to see which codes are supported and what they mean. A human readable form of this code is stored as the ReasonPhrase

• property StatusLine as %String;

The HTTP status line. This is the first line of the response and signals if the request was successful or if there was a problem.
Robert Cemper · May 6, 2022

Now with the class definition available, I understand(?) what you are looking for.
I see 2 possible solutions: embedded SQL or an Index on Title
#1

ClassMethod TitleToRowId(title) As %String 
    [ PublicList = (title, rowid, SQLCODE) ]
{
  &SQL(
     SELECT RowId into :rowid 
     FROM REST.TITLE 
      WHERE Title = :title
      )
  if 'SQLCODE quit rowid
  quit SQLCODE
}
 

btw: SQLCODE=0 means success. 
and you get the RowId by 

SET RowId=##class(REST.TITLE).TitleToRowId(obj.Title)  ;obj=JSON
SET task.Title = ##class(RESTAPI.TITLE).%OpenId(RowId)
SET book.Title = ##class(RESTAPI.TITLE).%OpenId(RowId) ; recent example

#2
 creating an Index on Title in REST.TITLE.
 but you have all trouble on duplicates, max. string length on that index
 So I'd position it as elegant but rather risky on maintenance
 

Robert Cemper · May 6, 2022

Now, this gets clear.
With the keyword IDKEY you replaced the default ID naming it RowID.

To store it:

set book=##class(BOOK).%New()
set book.RowId=obj.ID     ;  from JSON obj
set book.Title=obj.Title    ;  from JSON obj
do book.%Save()

to retrieve an existing Rowid:

set book=##class(BOOK).%OpenId(obj.ID)   ;from JSON obj
,;; access or change your book.Title
Robert Cemper · May 5, 2022

I'm sorry. it seems you don't understand what I'm talking about.
You just gave me the names. Not the structure and definition. 

Expected example:

Class RestApi.Books Extends %Persistent
{
Property Title As %String;
Property Pages As %Integer; 

Storage Default
{
<Data name="BooksDefaultData">
<Value name="1">
<Value>%%CLASSNAME</Value>
</Value>
<Value name="2">
<Value>Title</Value>
</Value>
<Value name="3">
<Value>Pages</Value>
</Value>
</Data>
<DataLocation>^RestApi.BooksD</DataLocation>
<DefaultData>BooksDefaultData</DefaultData>
<IdLocation>^RestApi.BooksD</IdLocation>
<IndexLocation>^RestApi.BooksI</IndexLocation>
<StreamLocation>^RestApi.BooksS</StreamLocation>
}
}
  
 Class RestApi.Title Extends %Persistent
{
Property Title As Books;
Property Text As %String; 

Storage Default
{
<Data name="TitleDefaultData">
<Value name="1">
<Value>%%CLASSNAME</Value>
</Value>
<Value name="2">
<Value>Title</Value>
</Value>
<Value name="3">
<Value>Text</Value>
</Value>
</Data>
<DataLocation>^RestApi.TitleD</DataLocation>
<DefaultData>TitleDefaultData</DefaultData>
<IdLocation>^RestApi.TitleD</IdLocation>
<IndexLocation>^RestApi.TitleI</IndexLocation>
<StreamLocation>^RestApi.TitleS</StreamLocation>
}
}


it's midnight now. I finish 

maybe next week.

Robert Cemper · May 5, 2022

Every Database in Caché or IRIS has a "NickName" (TEST, APP, USER, *TEMP, ..)
The file location is just a pointer related to the location of the file used
Similar Resource is an attribute to this "NickName".  and NOT to the related file
Changing it affects user access, but doesn't care at all about the file location.
The *.DAT file has no information about Resources or its NickName.  

Way back in the past, when file sizes were limited by file systems, there were
"Continuation" Files for Cache.DAT. Those knew the starting Cache.DAT.
But this is decades back and gone and doesn't exist anymore.