[jira] [Commented] (AVRO-2621) Practical CustomConversions with SpecificCompiler and Maven

["Dan Lipofsky (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AVRO-2621?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17124422#comment-17124422 ] 

Dan Lipofsky commented on AVRO-2621:
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I'm also working on money (JSR 354 instead of Joda, but I imaging the avro solution will be very similar) so I would really appreciate if any of you could share your work on implementing this.

> Practical CustomConversions with SpecificCompiler and Maven
> -----------------------------------------------------------
>
>                 Key: AVRO-2621
>                 URL: https://issues.apache.org/jira/browse/AVRO-2621
>             Project: Apache Avro
>          Issue Type: Improvement
>          Components: java
>            Reporter: Cherry Development
>            Priority: Major
>              Labels: maven
>
> So, as seen in AVRO-2498 we now have the ability in 1.9, at least using the Maven tools, to have generated classes with a field of type UUID. For some background, the secret sauce to get this working is:
>  * Set the logicalType of the field to 'uuid' and type to 'string'
>  * In the maven plugin configuration, add an item to <customConversions> with the value org.apache.avro.Conversions$UUIDConversion
> I attempted this with a custom type of my own (in this case, joda Money) first by implementing a CustomConversion<Money> class that created a new LogicalType called "money". This did not work, though, because although the maven mojo correctly added the CustomConversion to the SpecificCompiler, when the compiler parses the schema and sees the logicalType of type "money", it attempts to look up the LogicalType from LogicalTypes the LogicalType is not registered and it ignores it, which causes the field within the Schema to not have a logicalType. Without a logicalType, the compiler does not consider it a "UsedConversionClass" (see SpecificCompiler.getUsedConversionClass()) and they velocity template doesn't write the class with the custom field type.
> Trying to be clever, I attempted to work around this by putting a static initializer in my CustomConversion class which called LogicalTypes.register(). Unfortunately for me, the maven plugin doesn't load any of the classes specified in <customConversions> until AFTER it has parsed a schema.
> Obviously, putting a static initializer inside of a CustomConversion should not be part of a solution to this issue, but I propose a very simple solution:
>  * Add a logicalTypes property to AbstractAvroMojo, with items of a new type, LocalTypeDefinition. That type will have a name and a logicalTypeFactory.
>  * Upon startup of the mojo, iterate through each item and call LogicalTypes.register() on each, passing the indicated name and a new instance of the indicated logicalTypeFactory class.
>  * At this point, the existing logic will treat the new custom type the same as "uuid" is treated and will generate SpecificRecord classes with fields of that type.
> I could implement this pretty trivially, if there's an appetite for it. This would seem to be 100% backwards compatible.



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