Since the GetHashCode operation is critical to the success of any
nHibernate project how do people generally implement that function?
For tables without a timestamp I envision this:
public override int GetHashCode()
{
System.Text.StringBuilder sb = new
System.Text.StringBuilder();
sb.Append(this.GetType().FullName);
sb.Append(_userName);
sb.Append(_authorizationLevel);
return sb.ToString().GetHashCode();
}
And have all objects be derived from DomainObject as described here:
http://devlicio.us/blogs/billy_mccafferty/archive/2007/04/25/using-equals-gethashcode-effectively.aspx
Obviously for large tables with many fields it may not be very good to
make the hashcode out of all the columns. Therefore if there was a
timestamp column, wouldn't that be sufficient for the GetHashCode
function and look something like this:
public override int GetHashCode()
{
System.Text.StringBuilder sb = new
System.Text.StringBuilder();
byte[] byt =
System.Text.Encoding.UTF8.GetBytes(_timestampColumn);
sb.Append(this.GetType().FullName);
sb.Append(Convert.ToBase64String(byt));
return sb.ToString().GetHashCode();
}
Or would the overhead of converting to a base64 string be too much?
How do people typically do this with say a table with 60 columns.
Surely they don't add all the column data to one massive string do
they if they have a simpler timestamp column available to them?
On Jul 23, 8:18 am, John Davidson <[email protected]> wrote:
> Hold just the version key in session state as you describe should work fine
> in this scenartio.
>
> John Davidson
>
>
>
> On Fri, Jul 23, 2010 at 9:07 AM, MattO <[email protected]> wrote:
> > Okay, so it appears that I should be using the version property on an
> > object (wich I assume uses that GetHashCode stuff people recommend
> > using with nHibernate correct??).
>
> > Specifically it appears that I could just retain the version value in
> > session state and load the new database object from the database again
> > upon postback and then if the version key is the same then proceed
> > with the update.
>
> > But according to this example it almost looks like they are retaining
> > the entire "foo" instance in session state, which obviously would
> > consume much more memory then if you just retained the version value
> > in session state.
>
> > So how do people normally do it?
>
> > On Jul 23, 6:53 am, Roger Kratz <[email protected]> wrote:
> > > Have you read the manual about opt concurrency control?
> >http://nhforge.org/doc/nh/en/index.html#transactions-optimistic
>
> > > ________________________________________
> > > Från: [email protected] [[email protected]] för MattO
> > [[email protected]]
> > > Skickat: den 23 juli 2010 01:29
> > > Till: nhusers
> > > Ämne: [nhusers] ASP .NET, Concurrency, and nHibernate Questions
>
> > > NHibernate users,
>
> > > I'm pretty new to nHibernate and I've been watching the summer of
> > > nhibernate series (very good btw!). I've also read this:
> >http://www.codeproject.com/KB/architecture/NHibernateBestPractices.aspx
> > > and this:
> >http://nhforge.org/blogs/nhibernate/archive/2010/07/11/nhibernate-boo...
>
> > > All of those methods seem to suggest that Session Per Request is the
> > > way to go with nHibernate. Though this may work for multiple hits per
> > > session and speed things up, how do people do this for ASP .NET
> > > applications?
>
> > > My issue is that when I load the data via nHibernate the session goes
> > > away, and then when I want to save the data back to the database the
> > > data in the database may have already changed and I need to throw an
> > > exception to the user and give them the latest data.
>
> > > Can anyone provide a working code example on how they have handled
> > > this with the follow types of data:
>
> > > 1. Tables with timestamp columns
> > > 2. Tables without timestamp columns or any versioning columns to
> > > begin with, therefore I'm looking for the techniques in nHibernate
> > > that just pass in a huge WHERE SQL clause that compares all columns to
> > > make sure they are still the same and if not throws a concurrency
> > > violation. We have a lot of these due to legacy databases.
>
> > > Right now I have the session working on a per request basis in the
> > > ASP .NET demo application, but am looking for guidance on the
> > > concurrency issue (with code examples, and the appropriate HBM XML
> > > mapping examples).
>
> > > As I see it right now I need to have nHibernate go and retrieve the
> > > data from the database again, compare the timestamp value and if it is
> > > different then throw a concurrency violation to the user and give them
> > > the latest data to try update again.
>
> > > How have people done this in the past with highly volatile data using
> > > a stateless application such as ASP .NET? Any code examples you can
> > > point me to?
>
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