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https://issues.apache.org/jira/browse/AVRO-2723?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17032362#comment-17032362
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Ryan Skraba commented on AVRO-2723:
-----------------------------------
OK! Thanks for the explanation, I think I understand better.
In my experience, schemas generated through ReflectData have been usually
"short-lived" and infrequently use schema evolution (where the default
attribute is useful). I have no objection to improving how schemas are
created from POJO's via reflection, however!
I suspect that the *{{AvroDefault}}* solution was chosen precisely because it
permits generating the whole schema without having to instantiate an instance.
However, I'm pretty sure you *can* apply it to *{{Integer}}* and complex
classes.
For example, the following works:
{code:java}
static class DefaultTest {
@AvroDefault("1")
Integer foo;
}
static class ComplexDefaultTest {
@AvroDefault("2")
Integer bar;
@AvroDefault("{\"foo\":3}}")
DefaultTest inner;
}
{code}
A couple of things to consider:
1. there's already a *{{getDefaultValue(Field)}}*, which does something
slightly different than the method of the same name you propose -- I'd suggest
picking something more explicit. *{{createSchemaDefaultValue()}}* perhaps?
2. as you point out *{{ReflectData.AllowNull}}* (used in your example) always
generates nullable fields with null-first unions, which can only have
*{{null}}* as a default. You might want to switch the order of types in the
union if a non-null default is discovered.
I think the only existing solution today (without refactoring ReflectData)
would be to generated schema, then "massage" it manually to modify the defaults
that it gave you before saving it.
> Avro Java: Obtaining default values for POJO objects with ReflectData
> ---------------------------------------------------------------------
>
> Key: AVRO-2723
> URL: https://issues.apache.org/jira/browse/AVRO-2723
> Project: Apache Avro
> Issue Type: Wish
> Components: java
> Affects Versions: 1.9.1
> Reporter: Anh Le
> Priority: Critical
>
> Hi guys,
>
> I've got a simple app using Avro Reflection:
>
> {code:java}
> public class App {
> public static void main(String[] args) {
> testReflection();
> }
> static class User {
> public String first = "Andy";
> public String last = "Le";
> }
> static void testReflection(){
> // get the reflected schema for packets
> Schema schema = ReflectData.AllowNull.get().getSchema(User.class);
> System.out.println(schema.toString(true));
> }
> {code}
> The output on console will be:
> {noformat}
> {
> "type" : "record",
> "name" : "User",
> "namespace" : "App",
> "fields" : [ {
> "name" : "first",
> "type" : [ "null", "string" ],
> "default" : null
> }, {
> "name" : "last",
> "type" : [ "null", "string" ],
> "default" : null
> } ]
> }
> {noformat}
>
> As you can see, there's no default values for fields. Would you please tell
> me how to obtain such values?
> Thank you.
>
>
>
>
>
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