Andrew Olson created CRUNCH-667:
-----------------------------------
Summary: Documentation should mention that cogrouping requires a
common type family
Key: CRUNCH-667
URL: https://issues.apache.org/jira/browse/CRUNCH-667
Project: Crunch
Issue Type: Improvement
Components: Core
Reporter: Andrew Olson
Assignee: Josh Wills
Attempting to cogroup an Avro-based table with a Writable-based table produces
an exception like:
{noformat}
java.lang.ClassCastException: org.apache.crunch.types.writable.WritableType
cannot be cast to org.apache.crunch.types.avro.AvroType
at org.apache.crunch.types.avro.Avros.collections(Avros.java:409)
at
org.apache.crunch.types.avro.AvroTypeFamily.collections(AvroTypeFamily.java:106)
at org.apache.crunch.lib.Cogroup.cogroup(Cogroup.java:63)
at org.apache.crunch.lib.Cogroup.cogroup(Cogroup.java:46)
at
org.apache.crunch.impl.dist.collect.PTableBase.cogroup(PTableBase.java:176){noformat}
This technical limitation makes sense, and the exception message is relatively
self-explanatory (at least for anyone who is familiar with Crunch concepts), so
I don't think there's really a bug to be fixed. However both the documentation
in the code javadoc (Cogroup class, Set#difference, and PTable#cogroup) and the
user guide section about Cogroups
(https://crunch.apache.org/user-guide.html#cogroups) could be updated to
clarify that all tables involved in a cogroup operation must have the same type
family.
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