Thanks for the replies all,
That makes a lot of sense.
I'm curious if anyone has developed a nice, detailed way of displaying
the error to the user.
I basically just catch the exception from ec().saveChanges() and look
at the exception.getMessage() to see if there is a particularly named
constraint in there.
If there is, I make a validation message something like "Entity remote
ID must be unique" and spit the user back to the same page.
The two shortcomings of this are that you can't tell the user what
they entered (ie "123 has already been used" )
and you can't tell which Entity was in conflict if the given screen
has a list of many EOs and the user modified more than one remote IDs
at a time.
Any thoughts?
-Dan
On 26-Mar-09, at 1:01 AM, Ramon Havermans wrote:
Hi there,
Another advantage of letting the DB raise the exception is that it
is quicker. The db will just check all contraints on the db (the
unique one through an index) before inserting. If you do this
yourself you will do a fetch before the insert and than an insert if
its ok. Thats two actions for the db instead of one.
Kind regards,
Ramon
On Mar 25, 2009, at 8:51 PM, Chuck Hill wrote:
On Mar 25, 2009, at 12:46 PM, Dan Grec wrote:
Full of questions today....
I have an EO that has a field "RemoteSystemID" that must be unique
in the DB.
I have the constraint in the DB and that works well.
What I would like, is a way in EOF to detect non-uniqueness
without going to the db and relying on the SQL Exception.
Won't work, can't work, don't do it!
Currently, I have something like this:
@Override
public void validateForSave() throws
NSValidation.ValidationException {
validateRemoteSystemId();
super.validateForSave();
}
//check that no Categories have this same remoteSystemID
public void validateRemoteSystemId() {
NSArray<Category> categories =
SCEOFetcher.objectsMatchingKeyAndValue(editingContext(),
Category.class, _Category.REMOTE_SYSTEM_ID_KEY, remoteSystemId(),
EOFetcher.DBEC);
if (categories.count() > 1)
throw new NSValidation.ValidationException("Category Remote
System Id must be unique.", this, REMOTE_SYSTEM_ID_KEY);
}
This works really well if there is already one in the DB with a
value of say "123" and I try to add with with a value of "123".
This does not work if I try to add two at the same time with a
value of "567", it allows them both through.
Does anyone have a strategy to catch uniqueness at the EOF level?
Or, is it fine to just rely on the DB throwing an SQLException and
catch that after ec().saveChanges() ?
That is the only way to guarantee uniqueness. You can use the code
above to do a tentative validation (with the constraint still in
place on the DB), but the the DB has to be the ultimate authority
on what is and is not unique.
(I feel like letting that happen is bad, and might leave EOF in an
un-happy state - is there any chance of that?)
No. Failures in saveChanges at the database level are expected by
EOF and handled just fine.
Chuck
--
Chuck Hill Senior Consultant / VP Development
Practical WebObjects - for developers who want to increase their
overall knowledge of WebObjects or who are trying to solve specific
problems.
http://www.global-village.net/products/practical_webobjects
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