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From:Dan Nelson Date:July 29 2003 8:59pm
Subject:Re: Transactions
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In the last episode (Jul 29), b b said:
> Most web hosting companies run the mysql standard. Which means one
> can't run transactions. If that is the case, then how do you handle
> many to many relationships with truely normalized manner without
> risking data corruption
> For example: You have an org, ctry tables and a middle table orgCtry.
> The middle table has the two foriegn keys one from org and one from
> ctry. This way an org could be operating in many countries and a
> country could have many organizations.
> Now to insert an organization "AAA" that operates in USA, Canada, and
> Argentina one would need typically to do four sql statements:
>   insert into org(name, .....
>   get the newly inserted org ID 
>   insert into orgCtry(ID for org, ID for USA) ...
>     insert into orgCtry(ID for org, ID for Canada) ...
>   insert into orgCtry(ID for org, ID for Argentina)
> ...
>  To do the above securely one has to put it in a transaction. If

You really mean "To do the above atomically" here.  You can still do it
securely, but you have to make the client apppplication smarter.  If
the server crashes after the 2nd insert, you end up with 1 record in
orgName and 1 in orgCtry.  So when the end-user retries the request,
the client has to realize that AAA already exists and simply insert the
remaining two records.

When you decide to delete the "AAA" user, make sure you delete
dependent records first.  So remove the orgCtry records before removing
the parent record in org.  Otherwise, if the server crashes, you end up
with dangling records that you have to clean up in a maintenence script
(not difficult, but not necessary if you delete in the right order).

Transactions are most important in places where you have to update
multiple records or tables, and /cannot/ allow a partial update
(double-entry bookkeeping, etc).  Foreign keys (and subqueries) are
handy to have, but you can always duplicate their functionality with
extra code in the client.

	Dan Nelson
Transactionsb b29 Jul
  • Re: TransactionsDan Nelson29 Jul
    • Re: Transactionsb b30 Jul
      • Re: TransactionsPatrick Sherrill30 Jul
        • Re: Transactionsb b30 Jul
        • Re: TransactionsKaarel31 Jul
          • Re: TransactionsStephan Lukits1 Aug
  • Re: TransactionsPatrick30 Jul
  • Re: TransactionsPaul DuBois30 Jul
RE: TransactionsGilbert Wu30 Jul