Re: problem with LargeObject and commit - Mailing list pgsql-jdbc

Hi,

Attached is an attempt to do this (git diff on head).

The code seems to work. It has been tested on the program we are migrating
from SQL Server, we can now stream LOBs directly to web browsers...

Please note that I am not usually a Java developper. I did my best to do this
correctly, and the Java way (as far as I know :) ). If some things are not
done the right way, or there is a smarter solution, tell me, I'll improve
this.

Regards,

Marc

On Tuesday 01 October 2013 08:11:21 Dave Cramer wrote:
> Well I don't see any reason not to open up the LOM class to allow you to
> extend it.
>
> Can you send a git pull?
>
> Dave Cramer
>
> dave.cramer(at)credativ(dot)ca
> http://www.credativ.ca
>
> On Tue, Oct 1, 2013 at 3:52 AM, Marc Cousin <cousinmarc@gmail.com> wrote:
> > Sorry, I don't think I get it, so please correct me below if I didn't.
> >
> > I currently use getInputStream() on my large object. How could I provide a
> > connection to the extended InputStream ? I am calling a LargeObject
> > method.
> >
> > Or maybe extend LargeObject to have a new getInputStream method with a
> > connection provided, and then provide this connection to the extended
> > InputStream ?
> >
> > My initial idea was to not have to provide the connection as a parameter,
> > so I
> > wanted to use the Lob Manager.
> >
> > Anyway, shouldn't streaming a large object in this special case be easier
> > to
> > do ? The original code (from SQL Server) didn't have to do all these
> > workarounds, and I'll get this objection from people that will have to use
> > this code :)
> >
> > Just having conn as protected instead of private in the LargeObjectManager
> > would have made it possible to me to do it simply: I could have provided
> > the
> > connection to my extended LargeObject, and from there end the transaction
> > on
> > close().
> >
> > Regards.
> >
> > On Monday 30 September 2013 17:08:18 Dave Cramer wrote:
> > > Marc,
> > >
> > > You required the connection to create the LargeObjectManager, so why not
> > > just extend the InputStream and add the connection to that object.
> > > When you close the input stream, close the connection ????
> > >
> > > Dave Cramer
> > >
> > > dave.cramer(at)credativ(dot)ca
> > > http://www.credativ.ca
> > >
> > > On Mon, Sep 30, 2013 at 11:18 AM, Marc Cousin <cousinmarc@gmail.com>
> >
> > wrote:
> > > > Hi,
> > > >
> > > > I'm having the following problem: I need to stream a LOB to a web
> >
> > client,
> >
> > > > without consuming
> > > > a lot of memory. So I am returning getInputStream() to the caller.
> > > >
> > > > This works perfectly, except that I have to keep a transaction open to
> > > > return the large object
> > > > stream, and I have (or found) no way of closing the transaction when
> >
> > the
> >
> > > > filestream is closed.
> > > >
> > > > So of course, if I did that, I would get a lot of IDLE in transaction
> > > > sessions...
> > > >
> > > > So the logical way seemed to me to extend LargeObjectManager and
> > > > LargeObject to have a
> > > > close method on my LargeObject that closes the transaction, meaning
> >
> > that
> >
> > > > my LargeObject
> > > > should have a connection attribute. So I wanted to do something like
> >
> > this
> >
> > > > (not working,
> > > > it's just for the sake of explanation):
> > > >
> > > >
> > > > public class StreamLargeObjectManager extends LargeObjectManager{
> > > >
> > > >            public StreamLargeObject openStreamLargeObject(long oid,
> > > >            int
> > > >
> > > > mode)
> > > >
> > > >              throws SQLException
> > > >
> > > >            {
> > > >
> > > >              LargeObject lo = super.open(oid, mode);
> > > >              StreamLargeObject so = new StreamLargeObject(lo,
> > > >
> > > > super.getConn()); //cannot be done because no access to connection
> > > >
> > > >              return so;
> > > >
> > > >            }
> > > >
> > > > }
> > > >
> > > >
> > > > and
> > > >
> > > > public class StreamLargeObject extends
> > > > org.postgresql.largeobject.LargeObject{
> > > >
> > > >         Connection conn;
> > > >
> > > >         LargeObject lobj;
> > > >
> > > >
> > > >         public StreamLargeObject(LargeObject lg, BaseConnection conn)
> > > >
> > > > throws SQLException {
> > > >
> > > >                 this.lobj = lg;
> > > >                 this.conn = conn;
> > > >
> > > >         }
> > > >
> > > >
> > > >         @Override
> > > >         public void close() throws SQLException {
> > > >
> > > >                 lobj.close();
> > > >                 this.conn.commit();
> > > >
> > > >         }
> > > >
> > > >        public getInputStream() throws SQLException
> > > >
> > > >     {
> > > >
> > > >         return lobj.getInputStream();
> > > >
> > > >     }
> > > >
> > > > }
> > > >
> > > >
> > > > As the comment says it all, I cannot do this: conn is private in
> > > > LargeObjectManager. For now, the problem has been
> > > > worked around by duplicating all the LargeObjectManager code, but this
> >
> > is
> >
> > > > obviously ugly and not
> > > > maintainable. So my question is: have I missed some obvious solution ?
> > > > Could a getter be added to
> > > > the LargeObjectManager's connection ?
> > > >
> > > > Regards,
> > > >
> > > > Marc
> > > >
> > > >
> > > > --
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