Bug in Entity Framework

I found a great little bug in Entity Framework this morning.  One of their exception handlers can throw an exception, that hides the true exception.  Here’s how to recreate this:

1. Set your thread culture to a neutral culture:  i.e. ‘en’ instead of ‘en-US’
2. Create a new EF Context
3. Find an object (A) that has a dependency to another object (B) via foreign key and B has a dependency to object C via another foreign key.
4. Create a new object of type A called ‘a’
5. Get object B and detach it from the database (as if you were getting it in via a web service call).  B should lose it’s link to C
6. Add object B to A
7. Attempt to add A to the database via the context.AddToA(a)
8. Call context.SaveChanges().

What you should get is

System.Data.Entity  Type: System.Data.UpdateException  Message: Entities in '[contextName].B partticipate in the 'FK_B_C' relationship. 0 related 'C' were found. 1 'C' is expected.

What you will get is:

System.NotSupportedException: Culture 'en' is a neutral culture. It cannot be used in formatting and parsing and therefore cannot be set as the thread's current culture.     at System.Globalization.CultureInfo.CheckNeutral(CultureInfo culture)     at System.Globalization.CultureInfo.get_NumberFormat()     at System.Globalization.NumberFormatInfo.GetInstance(IFormatProvider formatProvider)     at System.Data.EntityUtil.ConvertCardinalityToString(Nullable`1 cardinality)     at System.Data.EntityUtil.UpdateRelationshipCardinalityConstraintViolation(String relationshipSetName, Int32 minimumCount, Nullable`1 maximumCount, String entitySetName, Int32 actualCount, String otherEndPluralName, IEntityStateEntry stateEntry)     at System.Data.Mapping.Update.Internal.UpdateTranslator.RelationshipConstraintValidator.ValidateConstraints()     at System.Data.Mapping.Update.Internal.UpdateTranslator.ProduceCommands()     at System.Data.Mapping.Update.Internal.UpdateTranslator.Update(IEntityStateManager stateManager, IEntityAdapter adapter)     at System.Data.EntityClient.EntityAdapter.Update(IEntityStateManager entityCache)     at System.Data.Objects.ObjectContext.SaveChanges(Boolean acceptChangesDuringSave)     at System.Data.Objects.ObjectContext.SaveChanges()  

The only way to get the real error, is to change your current culture from a neutral to a specific culture.  I’ve never seen this one before, and I had a few minutes of head scratching before we got the real cause.