Avro 模式定义嵌套类型

Question

我对 Avro 相当陌生，并且正在阅读有关嵌套类型的文档。下面的示例运行良好，但模型中的许多不同类型都有地址。是否可以定义 address.avsc 文件并将其作为嵌套类型引用？如果可能的话，您能否更进一步，为客户提供地址列表？提前致谢。

{"namespace": "com.company.model",
  "type": "record",
  "name": "Customer",
  "fields": [
    {"name": "firstname", "type": "string"},
    {"name": "lastname", "type": "string"},
    {"name": "email", "type": "string"},
    {"name": "phone", "type": "string"},
    {"name": "address", "type":
      {"type": "record",
       "name": "AddressRecord",
       "fields": [
         {"name": "streetaddress", "type": "string"},
         {"name": "city", "type": "string"},
         {"name": "state", "type": "string"},
         {"name": "zip", "type": "string"}
       ]}
    }
  ]
}

Answer 1

有4种可能的方式：

1. 如ticket 中所述，将其包含在 pom 文件中。
   
2. 在一个 avsc 文件中声明所有类型。
   
3. 使用单个静态解析器，首先解析所有导入，然后解析实际数据类型。
   
4. （这是一个 hack）使用 avdl 文件并使用像 https://avro.apache.org/docs/1.7.7/idl.html#imports 这样的导入。不过，IDL 是为 RPC 调用而设计的。
   

2 的示例。在单个 avsc 文件中声明所有类型。 还回答地址上的数组声明。

[
{
    "type": "record",
    "namespace": "com.company.model",
    "name": "AddressRecord",
    "fields": [
        {
            "name": "streetaddress",
            "type": "string"
        },
        {
            "name": "city",
            "type": "string"
        },
        {
            "name": "state",
            "type": "string"
        },
        {
            "name": "zip",
            "type": "string"
        }
    ]
},
{
    "namespace": "com.company.model",
    "type": "record",
    "name": "Customer",
    "fields": [
        {
            "name": "firstname",
            "type": "string"
        },
        {
            "name": "lastname",
            "type": "string"
        },
        {
            "name": "email",
            "type": "string"
        },
        {
            "name": "phone",
            "type": "string"
        },
        {
            "name": "address",
            "type": {
                "type": "array",
                "items": "com.company.model.AddressRecord"
            }
        }
    ]
},
{
    "namespace": "com.company.model",
    "type": "record",
    "name": "Customer2",
    "fields": [
        {
            "name": "x",
            "type": "string"
        },
        {
            "name": "y",
            "type": "string"
        },
        {
            "name": "address",
            "type": {
                "type": "array",
                "items": "com.company.model.AddressRecord"
            }
        }
    ]
}
]

3 的示例。使用单个静态解析器

Parser parser = new Parser(); // Make this static and reuse
parser.parse(<location of address.avsc file>);
parser.parse(<location of customer.avsc file>);
parser.parse(<location of customer2.avsc file>);

如果我们想要持有 Schema，也就是说，如果我们想要创建新记录，我们可以这样做 https://avro.apache.org/docs/1.5.4/api/java/org/apache/avro/Schema.Parser.html#getTypes() 获取模式的方法 或

Parser parser = new Parser(); // Make this static and reuse
Schema addressSchema =parser.parse(<location of address.avsc file>);
Schema customerSchema=parser.parse(<location of customer.avsc file>);
Schema customer2Schema =parser.parse(<location of customer2.avsc file>); 

Answer 2

只是为了添加到@Princey James 的答案中，嵌套类型必须在使用之前定义。

Answer 3

其他添加到@Princey James

使用 2 的示例。在单个 avsc 文件中声明所有类型。

它适用于序列化和反序列化代码生成

但是序列化和反序列化没有代码生成 不起作用

你会得到 org.apache.avro.AvroRuntimeException: Not a record schema: [{"type":" ...

代码生成的工作示例：

  @Test
  public void avroWithCode() throws IOException {

    UserPerso UserPerso3 = UserPerso.newBuilder()
                                    .setName("Charlie")
                                    .setFavoriteColor("blue")
                                    .setFavoriteNumber(null)
                                    .build();

    AddressRecord adress = AddressRecord.newBuilder()
                                        .setStreetaddress("mo")
                                        .setCity("Paris")
                                        .setState("IDF")
                                        .setZip("75")
                                        .build();

    ArrayList<AddressRecord> li = new ArrayList<>();
    li.add(adress);

    Customer cust = Customer.newBuilder()
                            .setUser(UserPerso3)
                            .setPhone("0101010101")
                            .setAddress(li)
                            .build();

    String fileName = "cust.avro";

    File a = new File(fileName);

    DatumWriter<Customer> customerDatumWriter = new SpecificDatumWriter<>(Customer.class);
    DataFileWriter<Customer> dataFileWriter = new DataFileWriter<>(customerDatumWriter);
    dataFileWriter.create(cust.getSchema(), new File(fileName));
    dataFileWriter.append(cust);
    dataFileWriter.close();

    DatumReader<Customer> custDatumReader = new SpecificDatumReader<>(Customer.class);
    DataFileReader<Customer> dataFileReader = new DataFileReader<>(a, custDatumReader);
    Customer cust2 = null;
    while (dataFileReader.hasNext()) {
      cust2 = dataFileReader.next(cust2);
      System.out.println(cust2);
    }
  }

没有：

  @Test
  public void avroWithoutCode() throws IOException {

    Schema schemaUserPerso = new Schema.Parser().parse(new File("src/main/resources/avroTest/user.avsc"));
    Schema schemaAdress = new Schema.Parser().parse(new File("src/main/resources/avroTest/user.avsc"));
    Schema schemaCustomer = new Schema.Parser().parse(new File("src/main/resources/avroTest/user.avsc"));

    System.out.println(schemaUserPerso);

    GenericRecord UserPerso3 = new GenericData.Record(schemaUserPerso);
    UserPerso3.put("name", "Charlie");
    UserPerso3.put("favorite_color", "blue");
    UserPerso3.put("favorite_number", null);

    GenericRecord adress = new GenericData.Record(schemaAdress);

    adress.put("streetaddress", "mo");
    adress.put("city", "Paris");
    adress.put("state", "IDF");
    adress.put("zip", "75");

    ArrayList<GenericRecord> li = new ArrayList<>();
    li.add(adress);

    GenericRecord cust = new GenericData.Record(schemaCustomer);

    cust.put("user", UserPerso3);
    cust.put("phone", "0101010101");
    cust.put("address", li);

    String fileName = "cust.avro";

    File file = new File(fileName);

    DatumWriter<GenericRecord> datumWriter = new GenericDatumWriter<>(schemaCustomer);
    DataFileWriter<GenericRecord> dataFileWriter = new DataFileWriter<>(datumWriter);
    dataFileWriter.create(schemaCustomer, file);
    dataFileWriter.append(cust);
    dataFileWriter.close();

    File a = new File(fileName);

    DatumReader<GenericRecord> datumReader = new GenericDatumReader<>(schemaCustomer);
    DataFileReader<GenericRecord> dataFileReader = new DataFileReader<>(a, datumReader);
    GenericRecord cust2 = null;
    while (dataFileReader.hasNext()) {
      cust2 = dataFileReader.next(cust2);
      System.out.println(cust2);

    }
  }