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https://issues.apache.org/jira/browse/AVRO-1827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16212536#comment-16212536
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Nandor Kollar commented on AVRO-1827:
-------------------------------------

Took a look at the latest patch, looks good to me. Though I'm not sure this can 
go in 1.8.x or 1.7.x release, since this is not a backward compatible 
modification. [~busbey] what do you think?

> Handling correctly optional fields when converting Protobuf to Avro
> -------------------------------------------------------------------
>
>                 Key: AVRO-1827
>                 URL: https://issues.apache.org/jira/browse/AVRO-1827
>             Project: Avro
>          Issue Type: Improvement
>    Affects Versions: 1.7.7, 1.8.0
>            Reporter: Jakub Kahovec
>            Assignee: Karel Fuka
>         Attachments: AVRO-1827.patch, AVRO-1827.patch, AVRO-1827.patch, 
> AVRO-1827.patch
>
>
> Hello,
> as of the current implementation of converting protobuf files into avro 
> format, protobuf optional fields are being  given default values in the avro 
> schema if not specified explicitly. 
> So for instance when the protobuf field is defined as  
> {quote}
> optional int64 fieldInt64 = 1;
> {quote}
> in the avro schema it appears as
> {quote}
>  "name" : "fieldInt64",
>   "type" : "long",
>   "default" : 0
> {quote}
> The problem with this implementation is that we are losing information about 
> whether the field was present or not in the original protobuf, as when we ask 
> for this field's value in avro we will be given the default value. 
> What I'm proposing instead is that if the field in the protobuf is defined as 
> optional and has no default value then the generated avro schema type will us 
> a union comprising the matching type and null type with default value null. 
> It is going to look like this:
> {quote}
>  "name" : "fieldIn64",
>   "type" : [ "null", "long" ],
>   "default" : null
> {quote}
> I'm aware that is a breaking change but I think that is the proper way how to 
> handle optional fields.
> I've also  created a patch which fixes the conversion
> Jakub 



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