Apache Avro：使用联合数据类型时出现 UnresolvedUnionException

Question

我正在使用Apache Avro进行对象序列化。

我有一个 AvroSchool对象架构：

{"namespace": "com.my.model",
 "type": "record",
 "name": "School",
 "fields": [
     {"name": "sid",  "type": "int"},
     {"name": "size",  "type": "long"},
     {"name": "other", "type": ["null", "Teacher", "Student"]}
   ]
}

正如您在上面看到的，该"other"字段保存一个联合数据类型，它可以是null一个Teacher实例或一个Student实例。

教师对象架构：

{"namespace": "com.my.model",
"type": "record",
"name": "Teacher",
    "fields": [
        {"name": "isMale", "type": "boolean"}
    ]
}

Student对象架构：

{"namespace": "com.my.model",
"type": "record",
"name": "Student",
    "fields": [
        {"name": "age", "type": "int"}
    ]
}

我使用 Avro 工具编译了上述模式，Avro 自动为我生成了所有 Java 类。

School然后，在我的 java 程序中，我通过以下方式创建实例：

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);

正如您在上面看到的，学校实例的other字段包含一个学生对象。然而，当我编译代码时，我得到了UnresolvedUnionException。它抱怨模式字段的联合数据类型。似乎无法解析我在 Java 代码中设置的内容。为什么会出现这个异常呢？堆栈跟踪是：otherSchoolstudentschool

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)

Answer 1

我可能会弄错，但我认为 Union 类型应该只包含一个非默认值：

{
    "name": "other",
    "type": [
        "null",
        "Teacher",
        "Student"
    ]
}

应该：

{
    "name": "other",
    "type": [
        "null",
        {
            "name": "Visitors",
            "symbols": [
                "Student",
                "Teacher"
            ],
            "type": "enum"
        }
    ]
}