Re: OOP/OOD Philosophy

> Because if you don't Oracle will print something you don't want to see.
The database should not print anything at all. Your application should
print it.

> TO_DATE and TO_CHAR are very important in Oracle, yet I've never seen
> them in any other Standard SQL database.
You shouldn't use to_date and to_char. Retrieve the dates as date
objects from the result set.

>> Almost all databases gives you the possibility to create your own
>> functions.
> Great but this discussion was about Standand SQL (and lack there of).
This is discussion is about how to make your application switchable
between different database vendors. ANSI SQL is obviously important for
this, but some problems can be solved in other ways, without having to
separate all database access in a separate layer. As a matter of fact,
there are an ANSI standard for stored procedues but it is poorly
supported.

> Having separate DDL statements (in
> a script I suppose?) is ugly duplication. The schema and app code get
> out of phase.
If you want your application to be able to change the schema, you need
a component with different implementations for different vendors.
Actually I already did it in Butler.

> "select
> fieldBlah from tableBlah" holds too much duplication, the field names
> and table name will be sprayed all over the place ...
If you have the same SQL statements or partly the same statement, you
shoud of course put it into a separate function/procedure/method. But
in a normal enterprise application there are many SQL statements that
are only used from one point in the application. In those cases,
decoupling will cause you extra work. Saying "the field names and table
name will be sprayed all over the place" is the same as saying "the
method names and class names will be sprayed all over the place".

If we do it your way, we will sooner or later be forces to use SQL
statement that do more things than we want like updating columns that
are not changed, joining tables that is not needed and selecting
columns we are not interested in.

> In Oracle you use yourSequence.NEXTVAL not NULL to get a new ID. I
> never thought of trying NULL but I can't see it working.
You are correct. I read the Oracle documentation and they recommed
using a trigger. In this case you will still have the same DML (insert)
statement for different databases.

> If you just stick closely to "Select * from Blah" or
> provide a truck load of workarounds yes you should be ok.
When we converted our HR application from Informix to also support
Oracle, the didn't have to to this. Just a small number of
"workarounds". Our application was mainly written in VB6 and other
obsolete languages using a 2-tier architechture. We had some java-code
with (switchable) data access object. The 2-tier code did not give us
almost any problems at all and we never had to use the different
implementations of the DAOs. That DAO-part of the architecture was
unnecessary.

> I forgot what mySQL does or doesn't do but I know it's different to
> Oracle and Oracle is different to SQL Server and Hypersonic and ...
If the correct transaction isolation level is choosen and a select
statement is made, every record that match to the where-clause should
be locked for writing. I think many vendors supports this.

> Transactions do not prohibit race conditions across multiple statements
> only locking can do that.
Transactions and locking work together. You can't have locking without
transactions. In the end of the transaction, the locks are released.

Fredrik Bertilsson
http://butler.sourceforge.net

.

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