Question

I’ve got a strange (correct me if I’m wrong) bug/feature with Linq to SQL that’s puzzling me and trying to understand what’s happening.

So I’ve taken the whole process procedurally in the hope of trying to find a resolution and have been unable to fix so far.

Here’s a repro of what is happening:

1. Record change made to database table “ETickets”. Changed column “availability” from 9
   to 8 (see below)
   Change made to database http://www.composeandshoot.com/soverflow/changemadetodb.jpg

2. Refresh page which has an ASP repeater databound to the ETickets table. This still displayed “9”.

3. Looked at quickwatch on the databinding to see what value was being returned from database (see below):
   quickwatch http://www.composeandshoot.com/soverflow/linqtosqlquickwatch.jpg

4. So I then took a look at the query running on the SQL server. Fired up SQL Server Profiler and got the following (see below):
   SQL profiler http://www.composeandshoot.com/soverflow/linqquery.jpg

5. Ran the query

   exec sp_executesql N’SELECT [t0].[id], [t0].[eventid], [t0].[availability], [t0].[cost]
   FROM [dbo].[ETickets] AS [t0]
   WHERE [t0].[id] = @p0′,N’@p0 uniqueidentifier’,@p0=’2642C0EF-C0C5-4881-9AC8-53C023B444D2′

6. SQL Server returns “8” as the availability! Yet the databinding still shows “9”. I’ve not enabled any SQL Cache Dependency.

Please could someone point me in the right direction here? Thanks.

Answer 1

What is the life-cycle of the data-context? Is it the same data-context, or a new one each time? (it should probably be the latter).

If you re-use a data-context, it is obliged to always give you back the same object when ever it seems the same identity. So if it has previously given you the version with 9, it’ll keep giving you back that reference even when the underlying data changes.

At the moment, this still does a round-trip; to avoid the round-trip, you need to use:

var obj = ctx.SomeTable.Single(x=>x.Id == id);

i.e. if it already has the object with Id == id in the local identity cache, it won’t perform a databae query at all.

any other construct will do a round trip. There is a fix in 4.0 so that .Where(x=>x.Id == id).Single() will avoid the round-trip, which should have with query syntax, i.e.

var obj = (from x in ctx.SomeTable
           where x.Id == id
           select x).Single();