DuplicateKeyException

[Ramesh Tiwari]

public int create(String [] data) throws DuplicateKeyException;is the method declaration in DBMain interface,here I don't see any possiblity for DuplicateKeyException because recno is the unique key and we don't specify recno when we create a record and we either a new record at the end or reuse a deleted record and when it comes repeating the data, a hotel can have multiple rooms with the same description for a customer.
Any ideas are appreciated.
Thanks

[Mike Southgate]

I interpreted this to mean that some of the fields in the database actually constituted a primary key. for my assignment this was Service Provider and Location (contractor assignment). But that's pure guesswork on my part...
ms

[Ramesh Tiwari]

Mike,thank you very much for your reply.
Does your assignment's documentation explicitly say what fields constitute primary key because docs for URLyBird 1.3.3 doesn't say anything like that, uniquesness is solely maintanied based on recno which is like a serial#.
The database that URLyBird uses contains 7 fields:
1)name(Hotel name)
2)location (city where this hotel is located)
3)size (maximum room occupancy)
4)smoking (smoking or non-smoking flag)
5)rate (charge per night for the room)
6)date (day for which this room is booked)
7)owner (customer name or ID who will occupy this room)
Nothing can be ever unique in the above fields even as a combination because a hotel can have multiple identical rooms and a customer can book multiple rooms in the same hotel for the same day.
recno is the only possible primary key,but we don't allow the client to choose recno i.e where he wants to store the record in the DB file, we control it from within the application.
Hence I don't see any scope for DuplicateKeyException.
Please let me know if you need more info.
Thanks

[Philippe Maquet]

Hi Ramesh,
I've got URLyBird 1.2.1 and I cannot define a primary key neither, because as you say, there is no field in our file against which we can test for uniquesness.
So I think that the use of a primary key for a given table is optional (could be used for example in a future customers table to make sure that all customers have a different ID). You could define it as :

String primaryKey;

and in createRecord() do something like this :

if (primaryKey != null) {
   checkDuplicate(); // throws DuplicateFieldException
}

But there is an issue in updateRecord() then :

it should do the same test but as it doesn't throw DuplicateFieldException, we cannot

or it should ensure that the primary key is never changed (but it would require one more specific exception too).

So another approach could be to ignore the primary key issue for the assignment telling in choices.txt why we did so :

no need for a primary key in the current URLyBird database

DBAccess don't let us implement such a key in a consistent way because of the updateRecord signature

Cheers,
Philippe.
[ July 24, 2003: Message edited by: Philippe Maquet ]

[Mark Spritzler]

I agree, the Hotel reservation system does not have a field combination to make a Primary key. Unless they would specifically say that a Hotel can only have one room of a certain type. But from what I hear that isn't there. So while I think a DuplicateKeyException is needed for a generic Database's create method. For this instance it doesn't appear to be valid.
However, I also would not remove this from the signature.
Good Luck. I don't have an real answer for this question which pops up very often with the Hotel Reservation System.
Hopefully Sun might be able to shed a little light on this discussion. Has anyone sent an e-mail to who2contact?
Mark