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https://issues.apache.org/jira/browse/THRIFT-1477?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13178850#comment-13178850
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Bryan Duxbury commented on THRIFT-1477:
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This feels like it would unnecessarily complicate the read() method. Can you
just figure out a way to do the name->id mapping yourself?
> Allow readFieldBegin() to pass back the field name instead of the field id
> --------------------------------------------------------------------------
>
> Key: THRIFT-1477
> URL: https://issues.apache.org/jira/browse/THRIFT-1477
> Project: Thrift
> Issue Type: Improvement
> Components: Java - Compiler
> Reporter: Benjy Weinberger
> Priority: Minor
>
> [Apologies if this has been addressed in another issue. I couldn't find
> anything relevant on JIRA or the mailing list archives.]
> Background: I'm implementing a BSON protocol, in order to write Thrift
> messages to MongoDB (technically the protocol generates the object
> representation that the MongoDB driver expects, not a raw BSON string
> directly to the transport, but that's an unimportant detail here).
> BSON, like JSON, naturally uses human-readable string field names.
> When reading, the generated Thrift code (at least in Java) requires that
> readFieldBegin() pass back a TField with the id field set. It ignores the
> name field. Therefore the ids must appear in the stream. It's possible to
> contort these protocols to use ids instead of human-readable names (as
> TJSONProtocol does) but this isn't helpful in dealing with prior BSON or JSON
> data that we're trying to back-port into Thrift schemata.
> However, the generated read() method already knows how to map names to ids.
> So I propose allowing a TProtocol's readFieldBegin() method to pass back a
> TField with the name set and no id set (indicated, say, by id==-1), and let
> the read() method figure out the id to then switch on.
> In some cases we could also allow the TField to omit the type information,
> which, again, is not naturally present in JSON. (BSON does embed type
> information, but its type system does not align fully with Thrift's, so it
> can't be used without further context). If the field is unknown, the only use
> for the type is for skipping the field value. But protocols like JSON and
> BSON can skip fields without this type information, since fields are
> delimited in the protocol in a type-independent way.
> Basically, what I propose is that readFieldBegin() be allowed to pass back
> just an id or just a name (and, for some protocols, no type information),
> since that is all read() needs in order to figure out how to read or skip the
> field.
> I'm wondering what the Thrift elders think of this. Has it been discussed?
> Thanks!
> PS This does have the downside that if Thrift were to implement a
> pass-through feature for unrecognized fields (so that new messages read with
> old protocol versions will serialize back out with no loss) - we wouldn't be
> able to preserve fields for which we only had a name and no id. Or rather, we
> wouldn't be able to write them out to a protocol that requires ids, like the
> binary protocols. However this feature doesn't exist anyway, and I don't know
> if it's on the roadmap.
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