如何返回 N1qlQueryResult 作为 Couchbase 数据库的 REST API 的响应?

I want to return the N1qlQueryResult as a response of my REST API. Below is the code:

@RequestMapping(value = "/test", method = RequestMethod.GET)
public @ResponseBody ResponseEntity<?> get() {
    List<N1qlQueryRow> result = null;
    try {
        Cluster cluster = CouchbaseCluster.create("localhost");
        Bucket bucket = cluster.openBucket("myBucket", "xyz");
        bucket.bucketManager().createN1qlPrimaryIndex(true, false);
        N1qlQueryResult queryResult = bucket.query(N1qlQuery.simple("select * FROM myBucket"));
        queryResult.forEach(System.out::println);
        result = queryResult.allRows();
    } catch (final Exception exception) {
        exception.printStackTrace();
    }
    return ResponseEntity.ok(result); 
}

我收到错误消息:

无法写入内容:找不到类的序列化程序com.couchbase.client.java.query.DefaultN1qlQueryRow 并且没有属性发现要创建 BeanSerializer(为避免异常，禁用SerializationFeature.FAIL_ON_EMPTY_BEANS)(通过引用链:java.util.ArrayList[0]);嵌套异常是com.fasterxml.jackson.databind.JsonMappingException:没有序列化程序为类 com.couchbase.client.java.query.DefaultN1qlQueryRow 找到并且没有发现创建 BeanSerializer 的属性(以避免异常，禁用 SerializationFeature.FAIL_ON_EMPTY_BEANS)(通过参考链:java.util.ArrayList[0])

Could not write content: No serializer found for class com.couchbase.client.java.query.DefaultN1qlQueryRow and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.ArrayList[0]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class com.couchbase.client.java.query.DefaultN1qlQueryRow and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.ArrayList[0])

解决办法是什么?我想以 JSON 的形式返回响应.

What is the solution? I want to return response as JSON.

推荐答案

ObjectMapper 默认在 bean 为 empty 时失败.我们可以像下面这样禁用它:

ObjectMapper by default fails when bean is empty. We can disable this like below:

ObjectMapper mapper = new ObjectMapper();
mapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);

但在您的情况下，它并不能解决问题，因为结果无论如何都是空的.返回不代表 POJO 本身的 type-s 并不是一个好主意.N1qlQueryResult 和 DefaultAsyncN1qlQueryRow 没有经典的 getters 和 Jackson 不能识别类似的方法 value() 默认情况下.我建议创建 Map<String, Object> 并手动构建所需的输出并包含所需的属性:

but in your case it does not solve a problem because result will be empty anyway. There is no good idea to return type-s which do not represent POJO itself. N1qlQueryResult and DefaultAsyncN1qlQueryRow do not have classic getters and Jackson does not recognise methods alike value() by default. I propose to create Map<String, Object> and build required output and include needed properties manually:

Map<String, Object> n1QlResult = new HashMap<>();
n1QlResult.put("status", result.status());
// other ...
n1QlResult.put("rows", result.allRows()
        .stream()
        .map(i -> i.value().toMap())
        .collect(Collectors.toList()));

最后返回:

return ResponseEntity.ok(n1QlResult);