Verifying the db file

[Inuka Vincit]

The requirments dont spell out how to verify the db file, just mentions that the cookie specifys it is a db file. I am not realy sure how flexible we are supposed to be with the db file. In my case I check
1. the cookie value to be the same value as give in my db file.
2. check the number of records to be 7.
2. the header information, which include the field lengths and field names to be the same as the requirements.

So even a slight change in the database file, such as a change in the field name would cause my Data object to throw an exception screaming incorrect data file format. I was wondering if I am being too strict in this regard or if I am misinterpreting something.

Any opinons would be appriciated

[Anton Golovin]

Hi, Inuka. I think verifying the cookie value as valid is sufficient to verify the validity of a data file. If, however, you would also like to verify that not only the file is valid, but its header section is also valid (and hence you can ppresumably read the records,) then of course one could argue for more extensive checks...

But there is one thing that may place unnecessary restrictions on the data in the data file. The header could be changed, presumably, in the future, and then the code would fail even though the data would still be valid as per new schema.
[ October 19, 2004: Message edited by: Anton Golovin ]

[Inuka Vincit]

Thanks Anton,
I am also thinking of adding a builder pattern to allow flexibility in the database and client(not sure yet). Eitherway I see what you mean.
[ October 19, 2004: Message edited by: Inuka Vincit ]

[William Ni]

Hi, Inuka:

I think step 2 - check the number of records to be 7 is unncessary. The database file would possibly grow as we are required to implement the createRecord method, unless you are referring to the very first initialization of the system.

I agree with Anton that checking the cookie value alone is sufficient. Meanwhile, I am curious about how you check the value. Do you
1. hardcode the value in your soucecode OR
2. set it and store it in the property file OR
3. guess it from the file name OR
4. some other ways...

What I found interesting is that the database file name reflects the magical cookie value. For my URLyBird 1.2.3 assignment, the db file is "db-1x3.db" and the magical cookie value is "00 00 01 03"; while my friend is doing the Contractor assignment, her db file is "db-2x2.db" and the magical cookie value is "00 00 02 02". Of course, this is a bad choice as no official guarantee is provided.

By checking the cookie value, do u mean we know the value prior to running the applicatoin? Though the value is not specified in the instruction.

[Inuka Vincit]

I read the cookie from the file I got and assumed it was the same for all. I think instead of checking for the exact value which I am doing now I am just going to check formatting.

[Manik Saha]

Originally posted by William Ni:

What I found interesting is that the database file name reflects the magical cookie value. For my URLyBird 1.2.3 assignment, the db file is "db-1x3.db" and the magical cookie value is "00 00 01 03"; while my friend is doing the Contractor assignment, her db file is "db-2x2.db" and the magical cookie value is "00 00 02 02". Of course, this is a bad choice as no official guarantee is provided.

This IS interesting.. it matches my file too.. db-1x2.db and the cookie is 01 02..

[jiju ka]

For db-1x2.db (for my assignment) magic cookie is 00 00 01 02.

William, You just uncovered something.

[Fred Beltr�o]

Just a curious observation: my URLyBird 1.2.3 db file name is db-1x3.db and the magic cookie is 00 00 01 03. I believe the magic cookie matchs the file name when Sun creates the file.

Best Regards.

[Paul Bourdeaux]

Good eye William!

Every few months or so, someone new on the forum makes this realization, and we have verified it over the course of time. The magic cookie used to verify the database file is indeed related to the database name. I believe the two are generated together.

[Olena Golub]

I saw a lot of topics where the magic cookie was something like this:
00 00 01 03

I read my cookies in this way:
int fileCookie = dbFile.readInt();
and i recieved e.g. 259
Is it Okey? Or should i read the cookie in another way?
Thanks a lot for your comments!
Olena

[Paul Bourdeaux]

Olena,

I believe you can read in your cookie which ever way you want. The verification is internal to the Data class, so it doesn't matter if you are using int or hex. The pattern was noticed in hex, that's all.