StreamInsight: Obscure LINQ error – Stream other than apply input stream is cannot be referenced inside apply branch

by | Nov 2, 2010 | BizTalk Community Blogs via Syndication

Another little LINQ error you might encounter from time to time.  Ran into this yesterday while building out some queries, and figured it was worth a quick post.  Starting with a basic stream, I needed to group by a set of fields in the stream and calculate some basic aggregates.

Code Snippet
  1. // This query calculates the sum of all sensor values
  2. //for each sensor
  3. //for each 5 seconds worth of data.
  4. var query = from e in inputStream
  5. group e by e.SensorId into sensorGroups
  6. from window in sensorGroups.TumblingWindow(
  7. TimeSpan.FromSeconds(5),
  8. HoppingWindowOutputPolicy.ClipToWindowEnd)
  9. select new
  10. {
  11. SensorId = sensorGroups.Key,
  12. Sum = window.Sum(e => e.Value)
  13. };

Running this throws the error:

Microsoft.ComplexEventProcessing.Linq.QueryGenerationException was unhandled by user code  
Message=Stream other than apply input stream is cannot be referenced inside apply branch. The 
following expression is not supported: 

'sensorGroups => CreateAdapterStream("input", 
StreamInsight.Samples.Adapters.SimpleTextFileReader.TextFileReaderFactory, value
(StreamInsight.Samples.Adapters.SimpleTextFileReader.TextFileReaderConfig), Point, value
(Microsoft.ComplexEventProcessing.Linq.CepStreamCreationContext)).TumblingWindow(FromSeconds(5), 
HoppingWindowOutputPolicy.ClipToWindowEnd)'.

See the subtle yet annoyingly obvious after the fact mistake I made?  I grouped by sensorGroups, but windowed over inputStream.  Fix this to use the same stream for the window and the group resolves the error.

Code Snippet
  1. var query = from e in inputStream
  2. group e by e.SensorId into sensorGroups
  3. from window in sensorGroups.TumblingWindow(
  4. TimeSpan.FromSeconds(5),
  5. HoppingWindowOutputPolicy.ClipToWindowEnd)
  6. select new
  7. {
  8. SensorId = sensorGroups.Key,
  9. Sum = window.Sum(e => e.Value)
  10. };