Re: prepared statements and sequences

Dave the scroll is getting longer....

On 2 Apr 2003, Dave Cramer wrote:

> Ryan,
>
> Scroll Way down :)
>
>
> On Wed, 2003-04-02 at 14:10, Ryan Wexler wrote:
> > Dave I couple more comments on the sequence
> >
> >
> > On 2 Apr 2003, Dave Cramer wrote:
> >
> > > See below, comments on sequence, I will have to look at the date problem
> > >
> > > On Wed, 2003-04-02 at 10:52, Ryan Wexler wrote:
> > > > Thanks for replying much appreicated my comments are inserted
> > > >
> > > >
> > > > On 2 Apr 2003, Dave Cramer wrote:
> > > >
> > > > >
> > > > > Ryan,
> > > > >
> > > > > See my comments below
> > > > >
> > > > > On Wed, 2003-04-02 at 00:43, Ryan Wexler wrote:
> > > > > > I am interfacing a postgresql db with jdbc using jdk1.4x on a linux box.
> > > > > > I have two questions/problems that I need help with.
> > > > > >
> > > > > > 1)Prepared Statments
> > > > > > I am trying to use a prepared statement and am successful except for date
> > > > > > fields. I get a parse error when using the preparedStatement.setDate(x,
> > > > > > java.sql.Date); Is this a postgres thing or a personal problem? Is there
> > > > > > a workaround?
> > > > > >
> > > > > Can you reproduce this in a small file? There was a similar question
> > > > > yesterday??
> > > > > >
> > > >
> > > > Here is the method I am calling. It is throwing the error on:
> > > > pStatement.setDate(4, new java.sql.Date(new java.util.Date().getTime()))
> > > >
> > > > The connection broker i created uses the "org.postgresql.Driver" driver
> > > > and has autocommit set to true.
> > > >
> > > >
> > > > public void insertOrder()
> > > > {
> > > > try
> > > > {
> > > > String query = "insert into customerorder (customer_id, address_id,
> > > > payment_id, createdate, ordertotal, tax, shipping, subtotal) " +
> > > > "values (?, ?, ?, ?, ?, ?, ?, ?)" ;
> > > > System.err.println(query);
> > > >
> > > > PreparedStatement pStatement= postgres.getPreparedStatement(query);
> > > > pStatement.setInt(1, 1);
> > > > pStatement.setInt(2, 1);
> > > > pStatement.setInt(3, 1);
> > > > pStatement.setDate(4, new java.sql.Date(new java.util.Date().getTime()));
> > > > pStatement.setBigDecimal(5, (new BigDecimal(123)).setScale(2,
> > > > BigDecimal.ROUND_HALF_UP));
> > > > pStatement.setBigDecimal(6, (new BigDecimal(123)).setScale(2,
> > > > BigDecimal.ROUND_HALF_UP));
> > > > pStatement.setBigDecimal(7, (new BigDecimal(123)).setScale(2,
> > > > BigDecimal.ROUND_HALF_UP));
> > > > pStatement.setBigDecimal(8, (new BigDecimal(123)).setScale(2,
> > > > BigDecimal.ROUND_HALF_UP));
> > > > int i = pStatement.executeUpdate(query);
> > > > System.err.println("i: " + i);
> > > >
> > > > }
> > > > catch (Exception x)
> > > > {
> > > > System.err.println("Exception: " + x);
> > > > x.printStackTrace();
> > > > }
> > > >
> > > > }
> > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > 2)Sequences-
> > > > > > I am using sequences as unique identifiers, or rather I should say I would
> > > > > > like to use sequences. I have successfully set up several sequences and
> > > > > > every time i insert an new row it automatically increments itself. My
> > > > > > problem is whenever I insert a row I need to know
> > > > > > what the sequence is that was associated with the row inserted. I
> > > > > > can't rely on doing a
> > > > > > max(sequenceid) kind of query because there maybe 10 rows inserted in that
> > > > > > time. My method of inserting rows is just using a prepared statement and
> > > > > > in my insert statement i don't reference the sequence. Is there a way to
> > > > > > get it to return the sequence id say when you call executeUpdate() on the
> > > > > > prepared statement? Or what is the proper way to do this?
> > > > >
> > > > > There is no way to get it to return the sequence. However you have two
> > > > > options here
> > > > >
> > > > > 1) get the sequence before the insert and insert it with the data.
> > > > >
> > > > > select nextval('sequence')
> > > > >
> > > > > 2) get the sequence after the insert
> > > > >
> > > > > select currval('sequence')
> > > > >
> > > > > Both of these methods are multi-connection safe, in other words if two
> > > > > connections are creating sequences at the same time, you will get the
> > > > > right data.
> > > > >
> > > >
> > > > ???
> > > > 1)If you use the nextval('sequence') method then can I assume when you
> > > > create your table you don't auto set it to be connected to the sequence
> > > > like:
> > > > CREATE TABLE "customerorder"
> > > > (
> > > > order_id integer DEFAULT nextval('order_id') UNIQUE not null,
> > > > customer_id integer not null,
> > > > address_id integer not null,
> > > > payment_id integer not null,
> > > > createdate date not null,
> > > > ordertotal numeric not null,
> > > > tax numeric not null,
> > > > shipping numeric not null,
> > > > subtotal numeric not null
> > > > );
> > > >
> > > Create the table just like above and use nextval, the sequence is only
> > > autoincremented when you omit the column on insert, or insert DEFAULT.
> > This pretty much clears me up, except when you say omit the DEFAULT
> > setting do you mean on the create table call, or in the insert?
>
> no, omit the column on the insert
>
> insert (customer_id) values (1) will auto increment the serial, as will
> insert (order_id, customer_id) values (DEFAULT, 1);

Ahhh now I see this will work perfect for me....

>
> > >
> > > > ???
> > > >
> > > > 2)How can you guarantee that between the select currval('sequence')
> > > > and the insertion that another value hasn't been inserted?
> > > The server does this for you.
> >
> > How can the server know this? What does it base it on?
> when nextval is called it remembers the value.
>
> try it. open two windows with psql do a select nextval( 'sequence' ) in
> each, then do select curval('sequence') in each
>
>

I believe you and I am going to try this, but there must be some basis.
Like do you have to use the same statment or connection or something like
that...

> >
> > Any thoughts on the date thing?
> I need some time to debug, and I am working on something else at the
> moment, will get to it before tomorrow.

Awesome dave this is much appreciated so I am using 7.3.1 if that helps

>
> > thanks
> > ryan
> >
> >
> >
> > > >
> > > >
> > > >
> > > >
> > > > -Ryan
> > > >
> > > >
> > > > > Dave
> > > > > >
> > > > > >
> > > > > > thanks a ton
> > > > > > ryan
> > > > > >
> > > > > >
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> > > > >
> > > > >
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> > >
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> Dave Cramer <Dave(at)micro-automation(dot)net>
>
>