Schema compatibility issue for schema registry

[Hao Ren]

Hi,

I have installed confluent platform v1.0.1 on my local PC.

When a schema is changed, even just add a field, it encountered an exception as the following:

Schema being registered is incompatible with the latest schema; error code: 409

You can easily produce this issue by run the following cmd:

curl -X POST -i -H "Content-Type: application/vnd.schemaregistry.v1+json" \

--data '{"schema": "{\"type\":\"record\",\"name\":\"test\",\"namespace\":\"lbc.test\",\"fields\":[{\"name\":\"first_name\",\"type\":\"string\"},{\"name\":\"age\",\"type\":\"int\"}]}"}' \

http://localhost:8081/subjects/test-key/versions

curl -X POST -i -H "Content-Type: application/vnd.schemaregistry.v1+json" \

--data '{"schema": "{\"type\":\"record\", \"name\":\"test\", \"namespace\":\"lbc.test\", \"fields\":[{\"name\":\"first_name\",\"type\":\"string\"}, {\"name\":\"age\",\"type\":\"int\"}, {\"name\":\"edu\",\"type\":[\"null\", \"string\"]} ]}"}' \

http://localhost:8081/subjects/test-key/versions

The second cmd just add a field called "edu" to the schema.

The "compatibility" of config is: backward. I have tried full and forward too. They don't work neither. "None" works fine, since it does not check schema compatibility.

It might be the workaround, but I still want to check schema.

Any help is highly appreciated.

Hao

[Ewen Cheslack-Postava]

Hi Hao,

Adding a field is only backwards compatible if the new field includes a default value. Using this command should work with compatibility set to the default "backwards":

curl -X POST -i -H "Content-Type: application/vnd.schemaregistry.v1+json" \

--data '{"schema": "{\"type\":\"record\", \"name\":\"test\", \"namespace\":\"lbc.test\", \"fields\":[{\"name\":\"first_name\",\"type\":\"string\"}, {\"name\":\"age\",\"type\":\"int\"}, {\"name\":\"edu\",\"type\":[\"null\", \"string\"],\"default\":null} ]}"}' \
http://localhost:8081/subjects/test-key/versions

(Note that I added "default": null to the "edu" field definition).

The reason the default is needed is that if you try to read a message in the old format with the new schema, the "edu" field will be missing. Since we need to fill it in with *something* to have a complete version 2 schema, it needs a default value. You can find a more detailed explanation in our docs here: http://docs.confluent.io/1.0.1/avro.html#backward-compatibility

-Ewen

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Thanks,
Ewen

[Hao Ren]

Thank you, Ewen.

It totally makes sense. =)

Thanks,
Ewen