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From Eric Wasserman <ewasser...@247-inc.com>
Subject RE: Schema not getting saved along with Data
Date Tue, 25 Mar 2014 16:25:48 GMT
Its a "must do".


The real requirement is the reader of the serialized records must have *exactly* the schema
that was used to write the records. [Note: The reader may also, optionally, specify an different
reader's schema that it would like the Avro parser to use to translate the deserialized records
into.]


How you arrange for the parser to get the writer's schema varies with your usage. If you happen
to use the org.apache.avro.file.DataFileWriter then it will prefix the file with the schema
used to write all the records. The corresponding DataFileReader will use the prefixed schema
to properly deserialize the records.


If you are putting serialized records into some other store, e.g. a database, and there is
a chance that the different records would be written with different schemas (or versions of
schemas), then you would want to include an indicator of the writer's schema (e.g. a hash
of the writer's schema or a foreign key to a schema's table) along with the record so that
at read time you could provide the correct writer's schema to your org.apache.avro.io.DatumReader.



________________________________
From: Sachneet Singh Bains <sachneets.bains@impetus.co.in>
Sent: Tuesday, March 25, 2014 7:18 AM
To: user@avro.apache.org
Subject: Schema not getting saved along with Data

Hi,

I am new to AVRO and going through the documentation.
>From http://avro.apache.org/docs/1.7.6/gettingstartedjava.html
"Data in Avro is always stored with its corresponding schema"

Does the above line convey a 'explicitly must do' or 'implicitly done' ?
Is it always true even when we write single records to any stream or applies only when  "Object
Container Files" are used ?
I tried writing some records to a file using DatumWriter and I see no schema saved along.
Please resolve my confusion.
Thanks,
Sachneet


________________________________






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