Hi Team, 

I could not yet get a proper working instance of an object with Database Tree 
property. Is there any reference I can check on detais of how I can use this? 
Everything I could find related with DBTree was on JIRA and they're not  clear. 

I see that I need a page hierarchy to display. Is it only a matter of 
parent-child relationship (if so, how can I inform to DBTree property the 
"root" of the hierarchy) or I can use the XE's native "relational" mechanism 
between objetcs, as I do with Database List? 

I've tested both approaches,  without success. I'm not using App within 
minutes, because I would like to learn and understand how this works to build 
bigger applications. 

Below is the example of what I'm trying to build.

Thanks again in advance, 
Ramon Brandão


-----Original Message-----
From: users [mailto:users-boun...@xwiki.org] in name of Ramon Gomes Brandao
Sent on: terça-feira, 24 de novembro de 2015 19:30
To: users@xwiki.org
Subject: [xwiki-users] Database Tree property Error on XE 7.1.2

Hi Xwiki Team,

I'm building an application on XE 7.1.2 and it uses classes with 1:N relations 
between them through Database List and (potentially) Database Tree property. 
The relation using Database Tree is not working. For illustration of my use 
case, I have the following classes:

Space.Info0Class with properties:
"info0ID" type String
"info0Name" type String

Space.Info1Class with properties:
"info1ID" type String
"info1Name" type String
"relatedInfo0" type Database List -> with Xwiki Class Name=Space.Info0Class, Id 
Field Name=info0ID and Value Field Name=info0Name

Space.Info2Class with properties:
"info2ID" type String
"info2Name" type String
"relatedInfo1" type Database Tree List -> with Xwiki Class 
Name=Space.Info1Class, Id Field Name=info1ID, Value Field Name=info1Name and 
Parent Field Name=relatedInfo0

The relation I want to build is, then: 1 Instance of Info0Class can be related 
to (0...N) Info1Class, which then can be related to (0...N) Info2Class.

When creating a new instance of Info2Class, I would like to show the 
information on relatedInfo1's  select box in a tree view manner, where the 
"relatedInfo0" instance name is the aggregator and all the related Info1Class 
instances are the leafs. Thus, the user can get a much better idea of which 
Info1Class she/he can select for relatedInfo1 field.

I've used, since then, only the default pages and codes generated by class 
editor (default sheet to display class properties and default template). I got 
the relation working like a charm between Info1Class and Info0Class, but things 
are not working with Info2Class and Info1Class. Creating a new instance of 
Info2Class triggers a
"org.apache.velocity.exception.MethodInvocationException: Invocation of method 
'display' in class com.xpn.xwiki.api.Document threw exception 
java.lang.StackOverflowError" and infinite 
"com.xpn.xwiki.objects.classes.DBTreeListClass.addToSelect(DBTreeListClass.java:319)"
 calls. In this way, I could not even check if this use case is valid for the 
Database Tree List.

I've searched deeply and really could not find any further documentation about 
Database Tree Usage, neither examples, nor detailed information on how to get 
this working. The only reference is a brief description on the XWiki Data Model 
Page mentioning the Yahoo Javascript Tree Library.

So, the questions for the team are:

1)      Where can I find more information (a good tutorial/documentation/usage 
example) about Database Tree List?

2)      Is it suitable for this use case? Am I doing it right?

3)      What do I need to get a Database Tree property/relation to work?



Thanks in advance for your help.
Best Regards,
Ramon Brandão
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