Refactor your table and move the unique stuff to an extra table and
enforce the DB-level uniqueness there?
Am 28.11.2005 um 11:09 schrieb Ondra Cada:
Hello,
My current customer needs a column which is semi-unique, i.e., some
of its values (programmatically determined which ones, in this case
those which happen to contain a decimal digit) need to be unique,
whilst others need not.
Of course, I can easily write a Java code to handle this kind of
"uniqueness", something conceptually like
void testAndSave() {
String uval=changedObject.uniqueValue();
if (shouldBeUniqueValue(uval)) {
NSArray a=EOUtilities.objectMatchingKeyAndValue
(changedObject.editingContext(),"uniqueValue",uval);
if (a.count()>0) throw new Exception("Not unique "+uval);
}
changedObject.editingContext().saveChanges();
}
I don't quite like this code though, for there still is a slight
possibility for two concurrent clients' operations may be ordered
so that both tests are all right, and then non-unique values are
saved. Since only some values are to be uniqued, I cannot use a
database unique constraint to prevent that (incidentally, am using
FrontBase -- not that it is important in this case).
What would be the best solution? Is there a standard way to make
such a test and save an atomical operation? I could lock or create
an explicit transaction I guess, but at the first look it seems to
be a bit overkill for such a plain task?
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