ahmedahamid commented on a change in pull request #2792: [GOBBLIN-933] add
support for array of unions in json schema
URL: https://github.com/apache/incubator-gobblin/pull/2792#discussion_r341779189
##########
File path: gobblin-core/src/test/resources/converter/jsonToAvroRecord.json
##########
@@ -1,4 +1,6 @@
-{"nullableField": null,
+{
+ "arrayFieldWithUnion": ["arrU1", "arrU2", "arrU3"],
Review comment:
Just following up: I tried adding a `null` value to this array but the
`JsonRecordAvroSchemaToAvroConverterTest.testConverter` failed:
```java
Could not convert field arrayFieldWithUnion
org.apache.gobblin.converter.DataConversionException: Could not convert
field arrayFieldWithUnion
at
org.apache.gobblin.converter.avro.JsonRecordAvroSchemaToAvroConverter.convertNestedRecord(JsonRecordAvroSchemaToAvroConverter.java:127)
at
org.apache.gobblin.converter.avro.JsonRecordAvroSchemaToAvroConverter.convertRecord(JsonRecordAvroSchemaToAvroConverter.java:71)
at
org.apache.gobblin.converter.avro.JsonRecordAvroSchemaToAvroConverterTest.testConverter(JsonRecordAvroSchemaToAvroConverterTest.java:69)
...
Caused by: java.lang.RuntimeException: Field: arrayFieldWithUnion is not
nullable and contains a null value
at
org.apache.gobblin.converter.avro.JsonElementConversionFactory$JsonElementConverter.convert(JsonElementConversionFactory.java:278)
at
org.apache.gobblin.converter.avro.JsonElementConversionWithAvroSchemaFactory$ArrayConverter.convertField(JsonElementConversionWithAvroSchemaFactory.java:98)
at
org.apache.gobblin.converter.avro.JsonElementConversionFactory$JsonElementConverter.convert(JsonElementConversionFactory.java:280)
at
org.apache.gobblin.converter.avro.JsonRecordAvroSchemaToAvroConverter.convertNestedRecord(JsonRecordAvroSchemaToAvroConverter.java:125)
... 51 more
```
I think the key issue here is that `UnionConverter` does not determine its
nullability correctly; it uses the nullability it receives from
`JsonElementConversionWithAvroSchemaFactory.getConvertor()` to decide its own
nullability. This is incorrect because even though `arrayFieldWithUnion` is a
non-nullable array, the union within its `items` _is_ nullable, i.e.
`UnionConverter` would return `false` if you invoke `isNullable()` on it even
though `["string", "null"]` is nullable because it is construing
`arrayFieldWithUnion`'s non-nullability as its own (see the values
`UnionConverter` provides to `super`).
One possible fix could be to have `UnionConverter` override `isNullable()`
so it can decide its own nullability based on its schemas, e.g.
```java
@Override
public boolean isNullable() {
return this.firstSchema.getType() == Schema.Type.NULL ||
this.secondSchema.getType() == Schema.Type.NULL;
}
```
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