[AVRO-1777] Select best matching record when writing a union in python

• Type: Improvement
• Status: Reopened
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.7.7
• Component/s: python
• Assignee: Daniel Kulp
• Reporter: Steven Aerts
• Created: 05/Jan/16 13:44
• Updated: 05/Apr/19 16:22

Description

Unlike javascript, python is not using wrapped types.
So when writing a union it needs to guess find out which type it will output.
At the moment it takes the last validating type.

I propose to take the type with the most matching fields.

So I propose to change in io.py:

# resolve union
index_of_schema = -1
for i, candidate_schema in enumerate(writers_schema.schemas):
  if validate(candidate_schema, datum):
    index_of_schema = i
if index_of_schema < 0: raise AvroTypeException(writers_schema, datum)

into

# resolve union
index_of_schema = -1
found_fields = -1
for i, candidate_schema in enumerate(writers_schema.schemas):
  if validate(candidate_schema, datum):
    nr_fields = candidate_schema.type in ['record', 'error', 'request'] and len(candidate_schema.fields) or 1
    if nr_fields > found_fields:
      index_of_schema = i
      found_fields = nr_fields
if index_of_schema < 0: raise AvroTypeException(writers_schema, datum)

If you want, I can create a pull request for this. And apply it both on py3 as py.

Issue Links

• links to: GitHub Pull Request #95
• links to: GitHub Pull Request #413