Java Avro 字段默认值
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Avro field default values
提问by Kesh
I am running into some issues setting up default values for Avro fields. I have a simple schema as given below:
我在为 Avro 字段设置默认值时遇到了一些问题。我有一个简单的架构，如下所示：
data.avsc:
数据.avsc：
{
"namespace":"test",
"type":"record",
"name":"Data",
"fields":[
{ "name": "id", "type": [ "long", "null" ] },
{ "name": "value", "type": [ "string", "null" ] },
{ "name": "raw", "type": [ "bytes", "null" ] }
]
}
I am using the avro-maven-plugin v1.7.6to generate the Java model.
我正在使用avro-maven-plugin v1.7.6来生成 Java 模型。
When I create an instance of the model using:
Data data = Data.newBuilder().build();, it fails with an exception:
当我使用: 创建模型的实例时
Data data = Data.newBuilder().build();，它失败并出现异常：
org.apache.avro.AvroRuntimeException: org.apache.avro.AvroRuntimeException: Field id type:UNION pos:0 not set and has no default value.
org.apache.avro.AvroRuntimeException: org.apache.avro.AvroRuntimeException: 字段 ID 类型：UNION pos:0 未设置且没有默认值。
But if I specify the "default" property,
但是如果我指定“默认”属性，
{ "name": "id", "type": [ "long", "null" ], "default": "null" },
I do not get this error. I read in the documentation that first schema in the union becomes the default schema. So my question is, why do I still need to specify the "default" property? How else do I make a field optional?
我没有收到这个错误。我在文档中读到联合中的第一个架构成为默认架构。所以我的问题是，为什么我仍然需要指定“默认”属性？我如何使字段可选？
And if I do need to specify the default values, how does that work for a union; do I need to specify default values for each schema in the union and how does that work in terms of order/syntax?
如果我确实需要指定默认值，这对联合如何工作；我是否需要为联合中的每个模式指定默认值以及它在顺序/语法方面是如何工作的？
Thanks.
谢谢。
采纳答案by Y.H.
The default value of a union corresponds to the first schema of the union (Source). Your union is defined as ["long", "null"]therefor the default value must be a long number. nullis not a long number that is why you are getting an error.
联合的默认值对应于联合的第一个模式 ( Source)。您的联合被定义为["long", "null"]因此默认值必须是一个长数字。null不是一个很长的数字，这就是您收到错误的原因。
If you still want to define nullas a default value then put null schema first, i.e. change the union to ["null", "long"]instead.
如果您仍想定义null为默认值，则首先放置空模式，即将联合更改为["null", "long"]。
回答by Rites
回答by blueberry
You must provide "default": nullnot "default": "null"in the schema to get the builder method working
您必须在架构中提供"default": nullnot"default": "null"才能使构建器方法正常工作
