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List:       avro-dev
Subject:    [jira] [Commented] (AVRO-1347) Improve name and alias matching for named schemas
From:       "Ravi (JIRA)" <jira () apache ! org>
Date:       2014-11-23 19:58:13
Message-ID: JIRA.12652454.1371062053000.2698.1416772693088 () Atlassian ! JIRA
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    [ https://issues.apache.org/jira/browse/AVRO-1347?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14222481#comment-14222481 \
] 

Ravi commented on AVRO-1347:
----------------------------

Same here.. If my Writer has upgraded to define aliases and create a Super Schema \
(that comprises of the aliases), then my old Readers would cease to work unless they \
are changed refer to the new Super Schema. Besides Schema Evolution mentioned by Igor \
this would also help different applications with different upgrade life-cycles to \
continue to work without getting errored out.

> Improve name and alias matching for named schemas
> -------------------------------------------------
> 
> Key: AVRO-1347
> URL: https://issues.apache.org/jira/browse/AVRO-1347
> Project: Avro
> Issue Type: Improvement
> Components: java
> Reporter: Vincenz Priesnitz
> Attachments: AVRO-1347.patch, AVRO-1347.patch
> 
> 
> When reading an avro file with a named schema, the aliases of the writers schema \
> are not taken into account; only the aliases of the readers are matched against the \
> writers name. Even if the writers aliases match the readers name, the schemas will \
> not be matched. For example, the following two enum schemas will not be matched, \
> even though they share a common alias.  {code}
> {
> 	"type"  : "enum",
> 	"name"  : "foo",
> 	"alias" : "CommonAlias",
> 	"symbols" : ["LEFT", "RIGHT"]
> }
> {code}
> {code}
> {
> 	"type"  : "enum",
> 	"name"  : "bar",
> 	"alias" : "CommonAlias",
> 	"symbols" : ["LEFT", "RIGHT"]
> }
> {code}
> In most cases, the DatumReader resolves records of different names or namespaces by \
> matching their fields.  Unfortunately, there are some cases, where this sort of \
>                 matching is not happening, but just the names are compared:
> * Other named nodes, like enums, fixed or fieldschemas are not matched this way. 
> * A record inside a union is also only matched by the full name. 
> The latter one is especially tricky, since two recordschemas that match \
> structurally but differ in name or space, are interexchangable until they are put \
> into an union, at which point an exception is thrown. I propose that two named \
> schemas are matched, when they share a common name or alias.  I implemented said \
> changes and added a java annotation @AvroAlias(alias, space) that allows one to add \
> an alias to a record, enum or field.



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