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https://issues.apache.org/jira/browse/AVRO-816?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13060048#comment-13060048
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Doug Cutting commented on AVRO-816:
-----------------------------------
Patch looks great. A few things we might consider changing before committing:
- The relationship between 'isSuperset' and 'unify' might be a bit clearer if
different names were used. 'isSuperset/union' would be confusing since 'union'
already has a meaning in Avro, so maybe 'subsumes/unify' would be slightly
better? What do you think?
- Unification currently ignores schema & record properties and field ordering.
This is fine, since they're not needed for reading, but probably should be
called out in the javadoc. Someone could add this as a feature later if they
need it.
- When default values differ maybe an exception should be thrown?
- Should a call to unifyAliases() be added to RecordSchema?
- I would prefer that the methods instead started like: {code}
if (type != RECORD)
return super.unify(other);
... {code} This removes a level of indentation from the bulk of the method
and makes it clear to the reader that no other cases are dealt with.
> Schema Comparison Utils
> -----------------------
>
> Key: AVRO-816
> URL: https://issues.apache.org/jira/browse/AVRO-816
> Project: Avro
> Issue Type: New Feature
> Components: java
> Reporter: Joe Crobak
> Assignee: Joe Crobak
> Priority: Minor
> Attachments: AVRO-816.patch, AVRO-816.patch
>
>
> From my post on the mailing list, and Doug's response:
> {quote}
> On 05/05/2011 10:29 AM, Joe Crobak wrote:
> > We've recently come across a situation where we have two data files with
> > different schemas that we'd like to process together using
> > GenericDatumReader. One schema is promotable to the other, but not vice
> > versa. We'd like to programmatically determine which of the schemas to
> > use. I did a brief look through javadoc and tests, and I couldn't find
> > any examples of checking if one schema is promotable to the other. Has
> > anyone else come across this?
> >
> > For some context, we're considering patching AvroStorage [1] to remove
> > the assumption that all files have the same schema. In our case, our
> > schema has evolved in that a field that was an int was promoted to a long.
> A boolean method that tells you if one schema is promotable to another
> would work in this case, but would not help in cases where, e.g.,
> different fields had changed in different versions. For example, in
> branched development, two branches might each add a distinct symbol to
> an enum. So I think you might be better off with a method that, given
> two schemas, returns their superset, a schema that can read data written
> by either.
> Such a method does not yet exist in Avro, but should not be difficult to
> add. Please file an issue in Jira if this sounds of interest.
> Doug
> {quote}
> I think it would be useful to have both of the methods that Doug mentioned in
> some sort of schema utils class.
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