当 json 中的字段不总是相同时的 Avro 模式

Question

我正在使用融合的 kafka 平台。为了向主题生成消息，我给出了一个包含 16 个字段的 Avro 模式。现在传入的记录将仅包含来自这 16 个字段的数据，但不是全部。正如 discussion 中指出的那样，为每个字段使用默认值没有帮助。这个问题的解决方案是什么？

示例代码：

var KafkaRest = require('kafka-rest');
var AvroSchemais = new KafkaRest.AvroSchema({
    "name": "Mydata",
    "type": "record",
    "fields": [
        { "name": "id", "type": "string" },
        {"name" : "data", 
                     "type" : {
                         "type" : "array",
                         "items" :{
                            "name":"manyfields",
                            "type":"record",
                            "fields" : [
                            {"name" : "ip", 
                             "type" : "string", 
                             "default" : "NONE"},

                            {"name" : "iptime", 
                             "type" : "string", 
                             "default" : "NONE"},

                            {"name" : "mcc", 
                             "type" : "string", 
                             "default" : "NONE"},

                            {"name" : "mnc", 
                             "type" : "string", 
                             "default" : "NONE"},

                              {"name" : "cid", 
                             "type" : "string", 
                             "default" : "NONE"},

                             {"name" : "lac", 
                             "type" : "string", 
                             "default" : "NONE"}
                    ]}}}]});
topic.produce(AvroSchema, {'id':'abcd','data': [{"ip":"12.12.12.12","lac":"1234"}]},function(err, res){
    if (err){console.log(err);}
    else{console.log(res);}
});

错误：

message: 'Conversion of JSON to Avro failed: Failed to convert JSON to Avro: Expected field name not found: iptime'

感谢任何帮助！！

Answer 1

从阅读 Avro specification 来看，默认值似乎应该让你做你想做的事：

default: A default value for this field, used when reading instances that lack this field

也许您使用的解串器没有为 JSON 编码实现此功能。同时，您可以使用 avsc 通过自动填充缺失的字段来解决此问题：

var KafkaRest = require('kafka-rest'),
    avro = avsc;

var attrs = {
  "name": "Mydata",
  "type": "record",
  "fields": [ /* ... */ ]
};
var AvroSchema = new KafkaRest.AvroSchema(attrs);
var type = avro.parse(attrs);

var withoutDefaults = {'id': 'abcd','data': [{"ip":"12.12.12.12", "lac":"1234"}]};
var withDefaults = type.clone(withoutDefaults); // All defaults are present here.

topic.produce(AvroSchema, withDefaults, function (err, res){
  if (err) { console.log(err); }
  else { console.log(res); }
});

当 json 中的字段不总是相同时的 Avro 模式

Avro Schema when no of fields in json are not always same

json

avro

apache-kafka