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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