Bug 2613 - Null pointer exception in System.Data.Linq.DataContext.SetEntitySetsQueries
Summary: Null pointer exception in System.Data.Linq.DataContext.SetEntitySetsQueries
Alias: None
Product: Class Libraries
Classification: Mono
Component: System.Data ()
Version: unspecified
Hardware: Macintosh Mac OS
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
Depends on:
Reported: 2011-12-22 13:18 UTC by Michael Thwaite
Modified: 2012-07-03 10:27 UTC (History)
1 user (show)

Is this bug a regression?: ---
Last known good build:

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Description Michael Thwaite 2011-12-22 13:18:36 UTC
I have a DataClassesDataContext brought over from VS (unable to build sqldb classes but that's for another day).

The underlying data structure comprises tables joined with foreign keys:

School ->
 FoodDaysRun ->
  FoodDay ->

There is also the relationship of

School ->

So, Themes belong to schools, and FoodDays have an individual Theme.

Here is the code (an empty ASP.NET solution, marked up with the failure:

		public virtual void button1Clicked (object sender, EventArgs args)
			DataClassesDataContext db=new DataClassesDataContext(); // OK
			School school =db.Schools.First (); // OK
			FoodDayRun fdr=school.FoodDayRuns.First (); // OK
			FoodDay fd=fdr.FoodDays.First (); // OK
			Theme theme=fd.Theme1; // FAIL returns: 500 error
//			System.NullReferenceException: Object reference not set to an instance of an object
//			  at System.Data.Linq.DataContext.SetEntitySetsQueries (System.Object entity) [0x00000] in <filename unknown>:0 
//			  at System.Data.Linq.DataContext._GetOrRegisterEntity (System.Object entity) [0x00000] in <filename unknown>:0 
//			  at System.Data.Linq.DataContext.Register (System.Object entity) [0x00000] in <filename unknown>:0 
//			  at DbLinq.Data.Linq.Sugar.Implementation.QueryRunner.Select[Theme] (DbLinq.Data.Linq.Sugar.SelectQuery selectQuery) [0x00000] in <filename unknown>:0 
//			  at DbLinq.Data.Linq.Implementation.QueryProvider`1[Theme].GetEnumerator () [0x00000] in <filename unknown>:0 
//			  at System.Data.Linq.EntityRef`1[Theme].get_Entity () [0x00000] in <filename unknown>:0 
//			  at FoodDay.get_Theme1 () [0x00000] in /Users/michael/Dropbox/Code/mono/FailDemo/FailDemo/DataClasses.designer.cs:4112 
//			  at FailDemo.Default.button1Clicked (System.Object sender, System.EventArgs args) [0x0002a] in /Users/michael/Dropbox/Code/mono/FailDemo/FailDemo/Default.aspx.cs:26 
//			  at System.Web.UI.WebControls.Button.OnClick (System.EventArgs e) [0x00000] in <filename unknown>:0 
//			  at System.Web.UI.WebControls.Button.RaisePostBackEvent (System.String eventArgument) [0x00000] in <filename unknown>:0 
//			  at System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent (System.String eventArgument) [0x00000] in <filename unknown>:0 
//			  at System.Web.UI.Page.RaisePostBackEvent (IPostBackEventHandler sourceControl, System.String eventArgument) [0x00000] in <filename unknown>:0 
//			  at System.Web.UI.Page.RaisePostBackEvents () [0x00000] in <filename unknown>:0 
//			  at System.Web.UI.Page.ProcessRaiseEvents () [0x00000] in <filename unknown>:0 
//			  at System.Web.UI.Page.InternalProcessRequest () [0x00000] in <filename unknown>:0 
//			  at System.Web.UI.Page.ProcessRequest (System.Web.HttpContext context) [0x00000] in <filename unknown>:0 
			button1.Text = string.Format ("{0}",theme.Name);
Comment 1 Michael Thwaite 2011-12-22 14:01:50 UTC
I've noticed something odd and specific to themes: the ID column (int) is the primary key but there is also a foreign key relation ship to itself. I'm going to test removing this to see the effect.

btw: this relationship works ok under VS/.net 4.0. but I'm finding that mono is far more struck about everything; I've already found and repairs dozens of wooly bits of code that VS/.NET let slide!
Comment 2 Michael Thwaite 2011-12-22 20:49:36 UTC
I've resolved the issue; there was a self-referencing fk theme.id <> theme.id which is stupid to be honest but .NET was ok with it!

Should this be tracked or a better error handler added?
Comment 3 Michael Thwaite 2012-07-03 10:27:56 UTC
Caused by bad db foreign key relationship.