public AmbientContextSuppressor()
{
_savedScope = DbContextScope.GetAmbientScope();
// We're hiding the ambient scope but not removing its instance
// altogether. This is to be tolerant to some programming errors.
//
// Suppose we removed the ambient scope instance here. If someone
// was to start a parallel task without suppressing
// the ambient context and then tried to suppress the ambient
// context within the parallel task while the original flow
// of execution was still ongoing (a strange thing to do, I know,
// but I'm sure this is going to happen), we would end up
// removing the ambient context instance of the original flow
// of execution from within the parallel flow of execution!
//
// As a result, any code in the original flow of execution
// that would attempt to access the ambient scope would end up
// with a null value since we removed the instance.
//
// It would be a fairly nasty bug to track down. So don't let
// that happen. Hiding the ambient scope (i.e. clearing the CallContext
// in our execution flow but leaving the ambient scope instance untouched)
// is safe.
DbContextScope.HideAmbientScope();
}
public void Dispose()
{
if (_disposed)
{
return;
}
if (_savedScope != null)
{
DbContextScope.SetAmbientScope(_savedScope);
_savedScope = null;
}
_disposed = true;
}
/// <summary>
/// Makes the provided 'dbContextScope' available as the the ambient scope via the CallContext.
/// </summary>
internal static void SetAmbientScope(DbContextScope newAmbientScope)
{
if (newAmbientScope == null)
{
throw new ArgumentNullException(nameof(newAmbientScope));
}
var current = CallContext.LogicalGetData(AmbientDbContextScopeKey) as InstanceIdentifier;
if (current == newAmbientScope._instanceIdentifier)
{
return;
}
// Store the new scope's instance identifier in the CallContext, making it the ambient scope
CallContext.LogicalSetData(AmbientDbContextScopeKey, newAmbientScope._instanceIdentifier);
// Keep track of this instance (or do nothing if we're already tracking it)
DbContextScopeInstances.GetValue(newAmbientScope._instanceIdentifier, key => newAmbientScope);
}
public TDbContext Get <TDbContext>() where TDbContext : DbContext
{
var ambientDbContextScope = DbContextScope.GetAmbientScope();
return(ambientDbContextScope?.DbContexts.Get <TDbContext>());
}
