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https://issues.apache.org/jira/browse/AVRO-171?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12770109#action_12770109
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Doug Cutting commented on AVRO-171:
-----------------------------------
It appears that a simple reverse is inadequate. We don't permit currently
forward references, which limits what can be represented, for example, we can't
currently express things like:
record A {B b}
record B {A a}
instead, one would have to structure this as something like:
record A {}
record B {}
record N { [A,B] ab, N n}
If we're willing to continue to accept that restriction, then ReflectData needs
to sort things in a topological-like manner here.
> Protocol Introspection can produce invalid forward references
> -------------------------------------------------------------
>
> Key: AVRO-171
> URL: https://issues.apache.org/jira/browse/AVRO-171
> Project: Avro
> Issue Type: Bug
> Components: java
> Affects Versions: 1.2.0
> Environment: java
> Reporter: Mr Fish
>
> Take a look at this code which is what happens in the SpecificResponder
> handshake.
> // server side
> final Protocol protocol =
> ReflectData.get().getProtocol(MyServiceIface.class);
> final String string = protocol.toString();
> // client side
> Protocol.parse(string);
> If you have a compound object made of
> class A {
> B1 b1;
> B2 b2;
> }
> class B1 {
> X x;
> }
> class B2 {
> X x;
> }
> class X {
> int i;
> }
> Then the types will be built up by RefectData.createSchema()
> A, B1, X, B2
> This is then reversed by RefectData.getProtocol() so B1 has no forward
> reference
> B2, X, B1, A.
> But this breaks B2
> org.apache.avro.SchemaParseException: Undefined name: "X"
>
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