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https://issues.apache.org/jira/browse/AVRO-1347?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13700214#comment-13700214
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Vincenz Priesnitz commented on AVRO-1347:
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Thanks a lot for the indepth review.
I moved the annotation to AVRO-1341. I think the annotation is still handy even
without writer schema aliases.
There are scenarios where it is not possible to add aliases to the readers
schema when using reflection, for example if i have no control over the class
or when reading an avro file with a specificreader, it is not possible to add
aliases to the reader.
The change is backwards compatible, but it enhances flexibility when using
reflection.
> 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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