Filip created AVRO-3583:
---------------------------
Summary: Avro ReflectData API does not allow referencing external
schemas through @AvroSchema
Key: AVRO-3583
URL: https://issues.apache.org/jira/browse/AVRO-3583
Project: Apache Avro
Issue Type: Bug
Components: java
Affects Versions: 1.10.2
Reporter: Filip
For easier transitioning into an Avro-based project, the {{ReflectData}} API
allows the generation of {{.avsc}} Schema files from POJOs.
However, currently it does not seem to be possible to reference external (from
the point of view of the POJO) schemas when doing so. Particularly, the
following case does not seem covered:
{code:java}
package com.acme;
public class Seller {
@AvroSchema("{\"type\":\"com.acme.Address\",\"name\":\"sellerAddress\"}")
private Address sellerAddress;
// getters/setters/constructors
}
// separate file
package com.acme;
public class Address {
private String street;
private String streetNumber;
// ...
// getters/setters/constructors
}{code}
trying to use e.g.:
{code:java}
ReflectData.AllowNull.get().getSchema(Seller.class)
{code}
currently throws the following exception:
{code:java}
org.apache.avro.SchemaParseException: Type not supported: com.acme.Seller {code}
{*}Note{*}: this does not have anything to do with forward references (which
are disallowed by Avro). The problem lies in
{{org.apache.avro.reflect.ReflectData#createFieldSchema}} which contains the
following code:
{code:java}
865 AvroSchema explicit = field.getAnnotation(AvroSchema.class);
866 if (explicit != null) // explicit schema
867 return new Schema.Parser().parse(explicit.value()); {code}
which explicitly (no pun intended) creates a new {{Parser}} instance which is
*not aware* of any other schema definitions that may have been processed
previously.
Not using {{@AvroSchema}} is obviously a possibility, but:
# Any POJO with more than a few fields will be needlessly complex and long,
# Care must be taken *not to reparse* the referenced class, since it would
lead to a redefinition of the schema and fail.
Is this intended behaviour? Is there a better way to generate schema files from
existing POJOs for non-trivial classes hierarchies?
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