[
https://issues.apache.org/jira/browse/AVRO-1811?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15362449#comment-15362449
]
Sean Busbey commented on AVRO-1811:
-----------------------------------
{quote}
Ryan Blue, this problem reminds me of the Logical Types. A logical type field
can have 2 representations: one uses raw type and the other uses upper level
java types. For instance, for "decimal" type, we can use both ByteBuffer and
BigDecimal. Do we need support copying between them?
{quote}
That's a very good question. What's the current behavior if we try to turn a
SpecificRecord that contains either representation into a GenericRecord?
{quote}
Above change is ugly. It only fixes the record copy problem. We may still face
the same problem in other scenarios. Maybe we should change the specific
compiler instead to make the setField method be able to accept different types
of values (for example, can accept both String and Utf8 for a string field)?
{quote}
That's interesting. It would make sense that the internal representation of the
data shouldn't constrain how we get bytes into it. Also, we're in a good
position to make sure that the String <-> Utf8 conversion is done correctly.
Presuming this fixes the immediate problem, I'd like this approach. I think
it's fine for the get methods to be asymmetric with the set methods, which is
the only drawback I can think of.
> SpecificData.deepCopy() cannot be used if schema compiler generated Java
> objects with Strings instead of UTF8
> -------------------------------------------------------------------------------------------------------------
>
> Key: AVRO-1811
> URL: https://issues.apache.org/jira/browse/AVRO-1811
> Project: Avro
> Issue Type: Bug
> Components: java
> Affects Versions: 1.8.0, 1.8.1
> Reporter: Ryon Day
> Assignee: Yibing Shi
> Priority: Critical
> Attachments: AVRO-1811.1.patch
>
>
> {panel:title=Description|titleBGColor=#3FA|bgColor=#DDD}
> When the Avro compiler creates Java objects, you have the option to have them
> generate fields of type {{string}} with the Java standard {{String}} type,
> for wide interoperability with existing Java applications and APIs.
> By default, however, the compiler outputs these fields in the Avro-specific
> {{Utf8}} type, requiring frequent usage of the {{toString()}} method in order
> for default domain objects to be used with the majority of Java libraries.
> There are two ways to get around this. The first is to annotate every
> {{string}} field in a schema like so:
> {code}
> {
> "name": "some_string",
> "doc": "a field that is guaranteed to compile to java.lang.String",
> "type": [
> "null",
> {
> "type": "string",
> "avro.java.string": "String"
> }
> ]
> },
> {code}
> Unfortunately, long schemas containing many string fields can be dominated by
> this annotation by volume; for teams using heterogenous clients, they may to
> want to avoid Java-specific annotation in their schema files, or may not
> think to use it unless there exist Java exploiters of the schema at the time
> the schema is proposed and written.
> The other solution to the problem is to compile the schema into Java objects
> using the {{SpecificCompiler}}'s string type selection. This option actually
> alters the schema carried by the object's {{SCHEMA$}} field to have the above
> annotation in it, ensuring that when used by the Java API, the String type
> will be used.
> Unfortunately, this method is not interoperable with GenericRecords created
> by libraries that use the _original_ schema.
> {panel}
> {panel:title=Steps To Reproduce|titleBGColor=#8DB|bgColor=#DDD}
> # Create a schema with several {{string}} fields.
> # Parse the schema using the standard Avro schema parser
> # Create Java domain objects for that schema ensuring usage of the
> {{java.lang.String}} string type.
> # Create a message of some sort that ends up as a {{GenericRecord}} of the
> original schema
> # Attempt to use {{SpecificData.deepCopy()}} to make a {{SpecificRecord}} out
> of the {{GenericRecord}}
> There is a unit test that demonstrate this
> [here|https://github.com/ryonday/avroDecodingHelp/blob/master/1.8.0/src/test/java/com/ryonday/avro/test/v180/AvroDeepCopyTest.java]
> {panel}
> {panel:title=Expected Results|titleBGColor=#AD3|bgColor=#DDD}
> As the schemas are literally identical aside from string type, the conversion
> should work (and does work for schema that are exactly identical).
> {panel}
> {panel:title=Actual Results|titleBGColor=#D55|bgColor=#DDD}
> {{ClassCastException}} with the message {{org.apache.avro.util.Utf8 cannot be
> cast to java.lang.String}}
> {panel}
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
