multiple references to only 1 object???

[Pieter]

Hi,

I've implemented some type of cache, to be able to point with multiple
references to the same object. Although, this 1-object-stuff is broken if I
do a refresh from the DataBase.

For instance I declare 2 objects:
dim MyA as clsCompany
dim MyB as clsCompany

And now I ask them from my factory:
'MyA: gets me the company with ID 1
MyA = MyFactory.GetCompanyWithID(1, enumFromCacheOrDataBase)
'MyB: Same thing, but because it's alreaddy in the ache, it returns me the
same object
MyB = MyFactory.GetCompanyWithID(1, enumFromCacheOrDataBase)
So it I change now a property of MyA, the same property will be changed in
MyB, because they poitn to the same object.

But: If I now explicitly do a refresh from the database, and replace the
object in the cache with the new one, I get something totally different:
MyB = MyFactory.GetCompanyWithID(1, enumFromDatabase)
If I change now a property of MyA, it won't be changed in MyB: they are
linked to 2 different objects now! What can I do to have them always being
linked to the same object? If I refresh one, all the others must point to
the new object...
Any help our hitns will be really appreciated!

Thansk a lot in advance,

Pieter

[Anthony Jones]

"Pieter" <pi****************@hotmail.comwrote in message
news:%2****************@TK2MSFTNGP05.phx.gbl...

Hi,

I've implemented some type of cache, to be able to point with multiple
references to the same object. Although, this 1-object-stuff is broken if

I

do a refresh from the DataBase.

For instance I declare 2 objects:
dim MyA as clsCompany
dim MyB as clsCompany

And now I ask them from my factory:
'MyA: gets me the company with ID 1
MyA = MyFactory.GetCompanyWithID(1, enumFromCacheOrDataBase)
'MyB: Same thing, but because it's alreaddy in the ache, it returns me the
same object
MyB = MyFactory.GetCompanyWithID(1, enumFromCacheOrDataBase)
So it I change now a property of MyA, the same property will be changed in
MyB, because they poitn to the same object.

But: If I now explicitly do a refresh from the database, and replace the
object in the cache with the new one, I get something totally different:
MyB = MyFactory.GetCompanyWithID(1, enumFromDatabase)
If I change now a property of MyA, it won't be changed in MyB: they are
linked to 2 different objects now! What can I do to have them always being
linked to the same object? If I refresh one, all the others must point to
the new object...
Any help our hitns will be really appreciated!

Thansk a lot in advance,

Once you've cached an object and supplied references to the object you
should not replace your cached object with a new instance. Instead provide
methods to re-load your objects internal state with new state gathered from
the DB.
--
Anthony Jones - MVP ASP/ASP.NET

[sloan]

I think you need to consider the Singleton design pattern.

http://www.dofactory.com/Patterns/PatternSingleton.aspx

And where the sample code has:
// Use 'Lazy initialization'
if (instance == null)
{
instance = new Singleton();
}

You'd have
instance = GetFromDatabaseSomehow(); //
You'll have to test this to see if it works for you or not. I think you'll
still run into a gotcha.

Are you doing this for webforms for winforms development? I'm guessing
winforms.
However, if something updates the singleton instance from another source,
you're gonna run into trouble.
I don't know if I've helped or not, take my advice with a grain of salt.
But I at least wanted to mention the Design Pattern.


"Pieter" <pi****************@hotmail.comwrote in message
news:%2****************@TK2MSFTNGP05.phx.gbl...

Hi,

I've implemented some type of cache, to be able to point with multiple
references to the same object. Although, this 1-object-stuff is broken if
I do a refresh from the DataBase.

For instance I declare 2 objects:
dim MyA as clsCompany
dim MyB as clsCompany

And now I ask them from my factory:
'MyA: gets me the company with ID 1
MyA = MyFactory.GetCompanyWithID(1, enumFromCacheOrDataBase)
'MyB: Same thing, but because it's alreaddy in the ache, it returns me the
same object
MyB = MyFactory.GetCompanyWithID(1, enumFromCacheOrDataBase)
So it I change now a property of MyA, the same property will be changed in
MyB, because they poitn to the same object.

But: If I now explicitly do a refresh from the database, and replace the
object in the cache with the new one, I get something totally different:
MyB = MyFactory.GetCompanyWithID(1, enumFromDatabase)
If I change now a property of MyA, it won't be changed in MyB: they are
linked to 2 different objects now! What can I do to have them always being
linked to the same object? If I refresh one, all the others must point to
the new object...
Any help our hitns will be really appreciated!

Thansk a lot in advance,

Pieter

[Jon Skeet [C# MVP]]

On Oct 16, 11:36 am, James Crosswell <[e-mail]:

See http://pobox.com/~skeet/csharp/singleton.htmlfor more info.

Nice - the nested class at the end it quite an elegant solution.

It's handy if you really need the extra laziness. I tend just to use a
static variable initializer.

PS: You wouldn't be able to chuck an RSS feed on those articles would you?

There already is one :)
http://www.yoda.arachsys.com/csharp/rss.xml

I haven't written a new article for a long time though, due to work on
the book. Hopefully when I've finished the book I'll suddenly find
myself with so much free time that I'll be dying to add more articles!

Jon