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https://issues.apache.org/jira/browse/AVRO-603?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12895028#action_12895028
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Doug Cutting commented on AVRO-603:
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> the readers schema is readily available with an instance of the generic object
That doesn't work well if the reader's schema is a union. The DatumReader
pre-computes re-mappings of fields, etc., so we don't want to specify a new
reader's schema per instance but rather one for a sequence of instances. I
guess we could check and only re-compute mappings etc. when the instance schema
is not double-equals to the previous instance's schema, but that would perform
poorly with unions.
> SpecificDatumReader requires the reader's schema to be set manually
> -------------------------------------------------------------------
>
> Key: AVRO-603
> URL: https://issues.apache.org/jira/browse/AVRO-603
> Project: Avro
> Issue Type: Improvement
> Components: java
> Reporter: Stu Hood
> Priority: Minor
>
> Since SpecificDatumReader has actual objects with schemas attached to them,
> it would seem that you wouldn't need to set the reader's schema: the default
> constructor only takes one schema argument, so it seems to support this, but
> behind the scenes, it sets the readers/writers to the same schema.
> Additionally, since DatumReader and its implementations use the terms
> 'expected' and 'actual' to refer to the 'reader' and 'writer' schemas,
> determining that you need to set the reader's schema requires a code dive,
> rather than a glance at the javadocs.
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