I am using [Apache Avro][1] for object serialization.
I have one Avro schema for `School` object:
{"namespace": "com.my.model",
"type": "record",
"name": "School",
"fields": [
{"name": "sid", "type": "int"},
{"name": "size", "type": "long"},
{"name": "other", "type": ["null", "Teacher", "Student"]}
]
}
As you see above, the `"other"` field holds an **union data type**, it could
be either `null` or a `Teacher` instance or a `Student` instance.
The **Teacher** object schema:
{"namespace": "com.my.model",
"type": "record",
"name": "Teacher",
"fields": [
{"name": "isMale", "type": "boolean"}
]
}
The **Student** object schema:
{"namespace": "com.my.model",
"type": "record",
"name": "Student",
"fields": [
{"name": "age", "type": "int"}
]
}
I compiled above schemas with Avro tool & Avro generated all the Java
classes for me automatically.
Then, in my java program I am creating `School` instance in the following
way:
School school = new School();
school.setSid(3);
school.setSize(2000);
//create a student object
Student student = new Student();
student.setAge(18);
//set student into school instance
school.setOther(student);
As you see above, the school instance's `other` field holds a student
object. When I compile my code, however I got the
**UnresolvedUnionException** . It complains about the **union data type**
for the `other` field of `School` schema. Seems it can not resolve the
`student` I set to `school` in my Java code. Why is this exception ?
Stacktrace is:
org.apache.avro.UnresolvedUnionException: Not in union
["null",{"type":"record","name":"Student","namespace":"com.my.model","fields":[{"name":"age","type":"long"}]},{"type":"record","name":"Teacher","namespace":"com.model","fields":[{"name":"isMale","type":"boolean"}]}]:
false
at
org.apache.avro.generic.GenericData.resolveUnion(GenericData.java:561)
at
org.apache.avro.generic.GenericDatumWriter.resolveUnion(GenericDatumWriter.java:144)
at
org.apache.avro.generic.GenericDatumWriter.write(GenericDatumWriter.java:71)
at
org.apache.avro.generic.GenericDatumWriter.writeRecord(GenericDatumWriter.java:106)
at
org.apache.avro.generic.GenericDatumWriter.write(GenericDatumWriter.java:66)
at
org.apache.avro.generic.GenericDatumWriter.writeArray(GenericDatumWriter.java:131)
at
org.apache.avro.generic.GenericDatumWriter.write(GenericDatumWriter.java:68)
at
org.apache.avro.generic.GenericDatumWriter.write(GenericDatumWriter.java:73)
at
org.apache.avro.generic.GenericDatumWriter.writeRecord(GenericDatumWriter.java:106)
at
org.apache.avro.generic.GenericDatumWriter.write(GenericDatumWriter.java:66)
at
org.apache.avro.generic.GenericDatumWriter.write(GenericDatumWriter.java:58)
[1]: http://avro.apache.org/docs/1.7.4/gettingstartedjava.html
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