Glenn Maynard wrote:
(JMdict?
yup. ;-)
I was playing with importing that into a DB a while back,
but the attributes in that XML are such a pain--and then my email died
while I was trying to get those changed, and I never picked it up
again.)
On Mon, Apr 13, 2009 at 1:20 PM, Stuart McGraw <smcg2...@frii.com> wrote:
1 to the number of sentences in the entry) and the sentence text. The pk is
of course the entry id and the sense number.
There are other tables that have fk's to the senses.
Your PK is a composite of (entry, order)? Won't your foreign keys
elsewhere all break when you shift the order around?
As Richard Broersma pointed out, the fk's are all
"cascade update".
I guess I could add an "order"[1] column and use the sense number as a
surrogate partial key to avoid the need for key renumbering,
but all the api's (and the normal human way of thinking) are based
on "sense number 1 of entry x", "sense number 2 of entry y", so
one would need to maintain "order" as a gapless sequence (or add a new
mapping layer to map from/to a arbitrary monotonic sequence
to a 1,2,3,... sequence) -- the gain doesn't seem that big.
Why not do this in the straightforward way: three separate fields: a
regular, sequential PK; an FK to the entry; and an order number. Add
an index on (entry_key, order_number). It's a little more expensive
since you have a new column and index (the PK), but in a table with a
lot of plain text that's probably insignificant. Now you can use the
plain PK for your FK's.
I have done a few other simple database apps in the
past and always did things that way. The current app
also started that way but I tried, experimentally, using
composite keys, and was amazed how much simpler things
became. For example, to copy an entry one duplicates
the entry's rows (in all the related tables) and need
only change the entry id number in the duplicated rows.
When each child table has a independent serial id, this
becomes more complicated and requires looping in the
copy function (AFAICT). I've noted that a number of
other things I was doing in the database api and in
Postgresql functions similarly became simpler.
I'd anticipate other problems with changing your PKs. If you're
referring to sense (100,3), and a concurrent user adds a sense, you
may suddenly find yourself referring to a different sense due to them
being reordered out from under you. You'd have similar problems if
your sense is deleted entirely: instead of the row simply ceasing to
exist (and resulting in predictable, checkable errors), you may end up
silently referring to another sense.
I try to avoid a lot of problems like that by doing very
little actual updating (in the database sense). Most
changes are made to a new copy of an entry. When an
update is actually done (such as to delete the original
copy of an entry), it is done in a very short time interval
with serializable isolation.
Maybe I'm misunderstanding what you're doing, though.
You'd have to have no UNIQUE constraint on the (entry, order)
composite index, though, or you'll have the same problem when you
reorder them.
Since the data in the database is of primary importance,
and the app(s) secondary, I really would like as much
constraint checking in the database as possible.
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