[jira] [Commented] (AVRO-816) Schema Comparison Utils

["Doug Cutting (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AVRO-816?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13058647#comment-13058647 ] 

Doug Cutting commented on AVRO-816:
-----------------------------------

I don't think this duplicates too much logic.

Alternately, the isSuperset method could be Schema#isSuperset(Schema that).  Then, instead of a big switch statement, you'd implement this method on Schema subclasses.  The base class, Schema, would implement this as just this.getType()==that.getType, handling int, byte, boolean and string.  NamedSchema would override this, checking names, etc.

Also, I worry that 'Arrays.asList(Type.INT, Type.LONG).contains(t)' may be slow, if performance matters.  't==INT || t == LONG' would be a lot faster and still readable.

> 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
>
>
> 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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