avro-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Doug Cutting <cutt...@apache.org>
Subject Re: static schema validation
Date Thu, 31 Jan 2013 18:39:21 GMT

You can use the SchemaNormalization class to test if two schemas are
effectively identical:


AVRO-816 has code to tell whether one Schema subsumes another (i.e.,
can, with resolution, read the other) and to combine multiple schemas
into a single that subsumes them all.


Bob Cotton recently suggested that we should commit some form of this.
 I'd be happy to do this if others agree.


On Wed, Jan 30, 2013 at 3:17 PM, Aaron Kimball <akimball83@gmail.com> wrote:
> Does Avro have an API to allow you to tell whether two schemas are a match,
> statically?
> i.e., schema1.canRead(schema2) /** return true iff schema1 can be used as a
> reader schema for schema2 */
> From my (admittedly cursorary) scan of the docs + source, it seems like
> there isn't something quite that concise, though maybe this can be
> accomplished using ResolvingGrammarGenerator?
> I'm pessimistic because of the following quote from the spec [1]
> [matching] if both are unions:
> The first schema in the reader's union that matches the selected writer's
> union schema is recursively resolved against it. if none match, an error is
> signalled.
> That sentence makes me think it's context dependent; I interpret "the
> selected writer's union schema" as "the schema of the actual thing written
> in a data buffer, which is one of the possible schemas the writer declared
> in her union type". i.e., you can only tell if schema R can be a reader for
> some other schema W in terms of a literal record written by W, and cannot be
> deduced statically for all possible records that can be encoded with schema
> W.  Is this interpretation correct? If so, does anyone have any ideas how to
> ensure the best bounds on statically-guaranteed backward compatibility
> between a given reader and writer?
> Thanks,
> - Aaron
> [1] http://avro.apache.org/docs/current/spec.html#Schema+Resolution

View raw message