This accounts for the totally weird results. Ref to "what [I] want".
As usual with software, I would like to make a change in one place vs
two or three places. I guess I am still thinking of this from a RDB
point of view. It sounds like you are telling me, that I must update
all of the relationships via explicit code references and then
commitChanges.
Is this correct?
On Dec 26, 2008, at 2:19 PM, Pierre Lavignotte wrote:
Hi Joe,
Question 1 :
you can't call the object constructor. Use the DataContext method
instead
because it will register the object too.
Question 2 :
It depends what you want !
DataContext dc = DataContext.
getThreadDataContext();
E1.getE2List().remove(e2);
dc.commitChanges();
This will remove the link between E1 and E2 but E2 will still exist.
DataContext dc = DataContext.
getThreadDataContext();
dc.deleteObject(e2);
dc.commitChangesToParent();
dc.commitChanges();
This will delete E2... but I think it will still be present in
E1.getE2List() because the list can be in memory.
I know it's not logical but I'm quite sure I allready encontered
this case.
I use Cayenne 2.0.4 so Cayenne 3.0 can differ in some points.
Pierre
Cordialement,
Pierre Lavignotte
Ingénieur Conception & Développement
http://pierre.lavignotte.googlepages.com
On Fri, Dec 26, 2008 at 6:32 PM, Joe Baldwin
<[email protected]>wrote:
I have a few questions about best practices. I have done some
experimenting, have read what I could find, and have some questions
about
some elementary Cayenne usage concerning Add & Delete with a
Parent-ChildList design. (I have recently experienced some odd
behavior
that may be due to a fundamental misunderstanding of DataContext
rules.)
Environment: I am using 3.0 M4 with MySQL and Tomcat JSP
DataContext: I am getting the context using:
DataContext.getThreadDataContext();
Example Design:
E1 has a list of E2's
that is:
E2 is a child of E1 and is a many-to-one relationship.
The E1 relationship is called "E2List" and the reverse
relationship
on E2 is called "E1".
Questions:
1. When creating and associating E2 children is it more proper to
do the
following:
DataContext dc = DataContext.getThreadDataContext();
** [get E1 via a DataContext query]
E2 e2 = new E2();
e2.setE1(e1); // I **assume** this registers e2 with the
Context &
adds e2 to e1's list
dc.commitChanges();
OR do you need to do as your example suggests:
DataContext dc = DataContext.getThreadDataContext();
E2 e2 = (E2) dc.newObject(E2.class);
e2.setE1(e1);
dc.commitChanges();
OR is there a better way?
2. Removal of a Child
Can you remove the child using:
DataContext dc = DataContext.getThreadDataContext();
dc.deleteObject(e2);
dc.commitChangesToParent();
dc.commitChanges();
or must you do it via the parent:
DataContext dc = DataContext.getThreadDataContext();
E1.getE2List().remove(e2);
dc.commitChanges();
(Note: the second method seems to work better.)
Thanks,
Joe
