Re: Saving entities problem [SOLVED]
Re: Saving entities problem [SOLVED]
- Subject: Re: Saving entities problem [SOLVED]
- From: Jevon Hills <email@hidden>
- Date: Tue, 29 Jul 2003 09:56:51 -0600
Thanx for your reply Art. As you may know this is not my first attempt
at trying to model the 3 way. With each attempt I get more into the WO
way and away from SQL.
I have just played around with eomodeler a little and would like to try
and explain what is happening as I understand it. Then if any of you
wish to 'correct' me, or 'nudge' me closer to the path (if I'm not on
it) that would be most appreciated. I have attempted to create these
models in ASCII ART, but this does not always work for me so I have put
the art at the bottom of my message so as not to mess things up too
badly.
WARNING: RATHER A LENGTHY MESSAGE FOLLOWS
THE TWO-WAY MODEL (MANY TO MANY) (See DIAGRAM 1)
I decided to create a new set of tables to work with: pubUser and
pubApplication.
I then created a new model using these tables. Using EOModeler I joined
the entities. (Join in Many to Many).
What it created was the Intermeadiate table (pubUserPubApplication) for
me with the to PK's as FK's and 2 relationships to the original
entities, but none of these would be visible to a Java Class (Class
Properties). In the original entities it also created two
relationships. One was a To-Many relationship to the Join entity (not a
class property) and the other a Flattened relationship to through the
join to the other Original Entity. (See DIAGRAM 1)
Then (as I understand it) in my code if I have an Application obj
(anApp) and wish to add a User obj (aUser) to it i write the following:
anApp.addObjectToBothSidesOfRelationshipWithKey(aUser, "pubUser");
This will essentially maintain the join for me.
Assuming that what I understand is correct I will now attempt to
transfer this to the 3-way model (Here's Hopin')
THE THREE-WAY MODEL (MANY TO MANY TO MANY) (See DIAGRAM 2)
Using 4 entities: pubUser, pubApplication, pubPermission, and
pubUserAppPerms.
Each of the primary entities there will be three relationships, two of
them will be Flattened and class Properties and one of them will be a
To-Many relationship that is not a class property. For example the
pubUser entity now has one attribute 'pubUserID' and 3 relationships:
'pubApps'(flattened relationship to
pubApplication),'pubPerms'(flattened relationship to pubPermission),
and 'pUserAppPerms' a To-Many relationship to the join table.
The join table will also have three attributes and three relationships,
but none of them will be class properties. Table pubUserAppPerms will
have pubUserID, pubPermissionID, and pubApplicationID as attributes and
pUser, pApp, pPerm as relationships to each entity.
In code then I believe I can do the following:
myClass
{
pubUser aUser;
pubApplication anApp;
pubPermission aPerm;
EOEditingContext editingContext;
aUser.addObjectToBothSidesOfRelationshipWithKey(anApp,
"pubApplication");
aUser. addObjectToBothSidesOfRelationshipWithKey(aPerm,
"pubPermission")
editingContext.saveChanges()
}
CONCLUSION (and it's about time. ed.)
I think that I understand a little more about EOModeler and its uses.
I hope that my ramblings were not too much and that they might help
others. Once again if I not directly on target, or Completly off the
Mark I hope that the members of the list will help correct my
inaccuracies.
ttfn
Jevon K. Hills
Developer - Zymeta Media Promotion Systems
ASCII Art Follows
KEY
PK - PrimaryKey
FK - ForeignKey
V - Class Property (visable)
DIAGRAM 1
----------------- --------------------
----------------
|pubUser | |pubUserApplication|
|pubApplication|
|---------------| |------------------|
----------------
|pubUserID PK |==============|pubUserID FK
|===============|pubAppID PK |
----------------- |pubAppID FK |
----------------
|pubApps V| |------------------|
|pubUsers V|
|pUserApps | |pUser |
|pUserApps |
----------------- |pApp |
----------------
--------------------
DIAGRAM 2
----------------- --------------------
----------------
|pubUser | |pubUserAppPerm |
|pubApplication|
|---------------| |------------------|
----------------
|pubUserID PK |==============|pubUserID FK
|===============|pubAppID PK |
----------------- |pubAppID FK |
----------------
|pubApps V| |pubPermID FK |
|pubUsers V|
|pubPerms V| |------------------|
|pubPerms V|
|pUserAppPerms | |pUser |
|pUserAppPerms |
----------------- |pApp |
----------------
|pPerm |
--------------------
=
=
=
=
=
-----------------------
|pubPermission |
-----------------------
|pubPermissionID PK |
-----------------------
|pubApps V|
|pubUsers V|
|pUserAppPerms |
-----------------------
On Monday, July 28, 2003, at 04:02 PM, Art Isbell wrote:
On Monday, July 28, 2003, at 06:21 AM, Jevon Hills wrote:
And set it's values
at.setPermission(canUse);
at.setApplications(mlp);
at.setUsers(aUsers);
And then save the changes
again(this.session().defaultEditingContext().saveChanges();)
**This Does not work.
On Monday, July 28, 2003, at 07:31 AM, Jevon Hills wrote:
The problem I had was my 3 FK columns would not accept nulls in
either the DB or the EOModel. When I was generating the object these
of course were null vaulus until the sql is generated. By allowing
nulls these worked just fine.
These primary key values should not be null, so I suspect by allowing
these to be null, you may be covering up another problem that will
come back to haunt you later (they always do :-)
The problem might be a modeling problem. EOModeler supports a
2-entity many-to-many relationship, but not a 3-entity many-to-many
relationship as in your case. So you'll need to build this manually.
This can be very tricky to do correctly. What I've done in similar
situations is let EOModeler build a 2-entity many-to-many relationship
and then copy exactly what EOModeler did but with 3 entities. This
requires examining each relationship EOModeler creates, setting the
relationship delete rules, propagate primary key property, etc.,
flattening proper relationships, ensuring that both the flattened and
underlying relationships aren't both class properties, etc.
The other problem might be your code. You shouldn't use relationship
setter methods directly; instead use
addObjectToBothSidesOfRelationshipWithKey(). This method will use
setter methods for both sides of each relationship; i.e. the
relationship and its inverse, if any. Failure to set both sides of
each relationship can result in the object graph being incomplete
which can lead to SQL that doesn't set database values correctly.
Aloha,
Art
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