On Thu, 2009-10-01 at 23:10 -0700, Peete wrote:
> The issue I have is that once I have loaded data into my generated
> table objects and try to load them again, I get old data.
> I make changes to the database from another program after I have first
> loaded the dblinq objects.
> Note that I have one Datacontext object in my app which is alive the
> whole time.
Don't do that. Seriously. Just Don't Do That. [0]
> If I use locally created datacontext object then it loads
> the data correctly.
Yeah. :-)
> Is there some kind of caching of data?
Yes. Caching is required in order to implement certain DataContext
behaviors [1].
> I have set QueryCacheEnabled to false but no difference.
That does something completely different. It doesn't control caching of
entities, it controls caching of DbLinq-generated queries, so that a new
query doesn't need to be created anew.
It's also horribly buggy (which is why it defaults to 'false', or
should).
- Jon
[0] Why not have a long-lived DataContext? For a number of reasons:
1. DataContext needs to cache all entity types returned from queries (so
that DataContext.SubmitChanges() can work [1]), so the longer the
DataContext lives, the larger the cache will become, and the more RAM
you'll use. This is...undesirable.
2. Large caches + lots of RAM use == slower performance (swapping = BAD)
3. DataContext wraps an IDbConnection, and IDbConnections CAN fail (due
to network errors, etc.; check the dblinq archives). Once the
IDbConnection is rendered invalid, the entire DataContext is also
invalid (because there's no way to "recreate" an IDbConnection instance
{unless the connection string provides the DbLinqConnectionType
parameter, but this doesn't help for the DataContext(IDbConnection)
constructor}). This is also bad.
For best overall performance, and for best DB interaction behaviors, you
want the DataContext to live for as short a period as possible.
[1] Example of required caching
var db = CreateDB();
var e = db.Employees.First();
e.FirstName = "Something Different";
db.SubmitChanges();
In order for the db.SubmitChanges() call to work, the DataContext needs
to know that 'e' exists, and thus store a reference to 'e' (so that it
can perform change tracking). This "stored reference" is a cache. QED.
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