2 Oct
2009
2 Oct
'09
11:24 p.m.
another quick answer ;)
On Fri, Oct 2, 2009 at 7:49 PM, Niels Mayer <nielsmayer(a)gmail.com> wrote:
On Thu, Oct 1, 2009 at 10:37 AM, Pascal Voitot <
pascal.voitot.dev(a)gmail.com>
wrote:
I don't know any samples or tutorials... I discovered by experience :)
A quick answer from a user who uses classes quite
intensively...
you can create links to other class instances (or objects) in your class
by
using the "Database List" property type
for example. It is very powerful
when you want to create a field of a class where values are stored in
another class and created dynamically. [...]
Thanks for helping me better understand this feature of Xwiki.
http://platform.xwiki.org/xwiki/bin/view/DevGuide/DataModel mentions:
- Database List
- Database Tree List
but the only explanation I'm finding quickly is
http://platform.xwiki.org/xwiki/bin/view/DevGuide/DsXWikiDatabaseListClasses
and
http://dev.xwiki.org/xwiki/bin/view/Drafts/DatabaseListProperties .
Are there any examples, tutorials or documentation, or just pointers to
source-code using this technique?
Questions: Is there an overall performance penalty
with adding database
list
fields that doesn't occur with a regular type such as a string or static
list? Does the associated database query only happen when the databaselist
properties are .get()'d explicitly? Also, most of the document properties
allow "setting". I assume databaselist and databasetreelist are "read
only"
and are not quite analogous to the list-type property, where you could
set/edit one or more selections, and then retrieve them back again. Or are
these just like other document properties (e.g. list) where values can be
get/set, the databaselist just determines the set of permissible values
dymamically, presents them when the property is edited, and validates
against them when the property is set.
Naturally this is not a Java-like list... this database list is just a list
of values where possible values are retrieved from fields of objects of
another XWikiClass... and these values shall be string values as far as I
can remember... it is simply a list of options dynamically built from DB...
I also remember that the value of the field is stored directly in the parent
object property. This means the parent object doesn't store the id of the
link object but the value of a field of the link object.
So naturally there is a performance penalty when you retrieve the possible
values from the instances of the link XWikiClass. But this is much more
dynamic than a static list...
But if you link your database list with a field of a XWikiClass that is
managed as a primary key (unique value), using a simple XWiki request, you
can retrieve the linked object itself quite easily and it behaves as if you
had a link between 2 objects. You do manually the work hibernate could do
for you and it might not be as performant as hibernate could do but in many
cases this is more than enough and so easy to use in XWiki...
BTW, in looking up info on this, I found these
helpful:
http://markmail.org/message/dhkrfddcli6fne7m
http://lists.xwiki.org/pipermail/users/2007-November/009471.html
Sergiu's explanation was the most helpful:
http://osdir.com/ml/web.wiki.xwiki.user/2008-02/msg00135.html
(I'll reproduce here to save you from the advertising on osdir.com)
-----------------------
horbjørn Konstantinovitz wrote:
> The second way to define the option
lists is by using the fields: XWiki
Class Name, Id Field Name, Value Field Name and Parent Field Name. Using
those fields, the XWiki platform constructs the following hql queries:
Niels
http://nielsmayer.com
_______________________________________________
devs mailing list
devs(a)xwiki.org
http://lists.xwiki.org/mailman/listinfo/devs
> Hi,
I am currently developing a program documentation
system based on xwiki.
I am able to create pages which describes
programs. For each program
which has to be described I programatically
creates a page and populate
a object with static program information. But I
need to document which
database files the program uses, with links to
the relevant database
file descriptions (a list). For that I want to
use a database list
class. I also want to show a call graph. for that
I want to use a
database tree class. But I am not able to find
any documentation on
these class properties. Can anyone give an
example of use for each of
these two properties or give pointers to relevant
examples.
on the server side were a very good introduction!
But it didn't treat
the property Custom Display. Are there any
documentation on this
property?
Cheers
/Thorbjørn Konstantinovitz
First, a bit of introduction on DBList and
DBTreeList.
StaticList properties, when edited, allow the
user to select one of the
predefined values (or more, if the property has "multiple select" =
true). DBList does something similar, allows the user to select one or
more values from a list of values, but the list is not predefined, it is
populated with values from the database.
DBTreeList does the same as DBList, but also
induces a pseudo-hierarchy
in the option list, displaying the options as a tree.
DBList and DBTreeList properties work in two
ways.
One is with an hql query, which allows complete
flexibility on what you
want to select. For DBList you select one or two columns. The first
column is the list of possible values that get into the option list. The
second (optional) column allows to separate the actual value that gets
stored in the database, and the values that are displayed to the user.
This allows, for example, to store XWiki.JohnDoe in the database, but to
display "Doe, John" in the interface. If only one column is selected,
the value displayed is the same as the value used internally.
DBTreeList queries must select 3 columns. The
first two are the same as
for DBList, while the 3rd column defines the child<->parent relations.
Selected rows that have null or an empty string on the third column will
be considered the roots of the tree. Rows that have a value "X" on the
third column will be inserted as child nodes of the node with value "X"
(the first column).
select idprop.value, valueprop.value,
parentprop.value from
XWikiDocument doc, BaseObject obj, StringProperty idprop, StringProperty
valueprop, StringProperty parentprop.value where obj.name = doc.name and
obj.className = "value entered in Class name" and idprop.id.id = obj.id
and idprop.id.name = "value entered in Id Field Name" and
valueprop.id.id = obj.id and valueprop.id.name = "value entered in Value
Field Name" and parentprop.id.id = obj.id and parentprop.id.name =
"value entered in Parent Field Name"
So, it selects from objects of a given type
(XWiki Class) 3 properties
(of storage type String, read bellow what this means). As a special
case, you can use "doc.<some doc property>" or "obj.<some object
property>" instead of property names, and the query is adapted
accordingly. In the case of DBList, only 2 columns are selected, as the
Parent property is not used/defined.
String storage type means:
- either a property of type String
- or a property of type StaticList, DBList or DBTreeList with
multipleSelect = false
If you want to use the DBTreeList, you must model
your data so that they
will allow these kind of queries.
--
Sergiu Dumitriu
http://purl.org/net/sergiu/
<
http://platform.xwiki.org/xwiki/bin/view/DevGuide/DsXWikiDatabaseListClasses