从 Spring 数据 MongoDB 的集合中获取简单平均值

Question

我需要获得所有迭代的平均持续时间。我有下面解释的实体实体：

@Document(collection = IterationEntity.COLLECTION_NAME)
public class IterationEntity {

    public final static String COLLECTION_NAME = "iterations";

    @Id
    private ObjectId id;

    @Field("start_date")
    private Date startDate;

    @Field("finish_date")
    private Date finishDate;

    @Field("duration")
    private Long duration;

    @Field("total_tasks")
    private Integer totalTasks = 0;

    @Field("total_failed_tasks")
    private Integer totalFailedTasks = 0;

    @Field("total_comments")
    private Integer totalComments = 0;

    @Field("tasks")
    @DBRef
    @CascadeSave
    private Set<TaskEntity> tasks = new HashSet<>();

}

我已经实现了一个自定义存储库方法来执行此操作，但是当我得到结果时出现错误。

@Override
    public Long getAvgDuration() {

        GroupOperation avgOperation = Aggregation.group()
            .sum("duration")
                .as("total_duration")
            .avg("total_duration")
                .as("avg_duration");

        Aggregation aggregation = newAggregation(IterationEntity.class, avgOperation);

        return mongoTemplate.aggregate(aggregation, IterationEntity.COLLECTION_NAME, Long.class).getUniqueMappedResult();

    }

执行该方法时出现此异常：

org.springframework.data.mapping.model.MappingException: No mapping metadata found for java.lang.Long

提前致谢。

Answer 1

为了正确映射聚合结果，需要将其映射到域类型或简单地返回 Document。
像下面这样的东西应该可以满足您的需求。

class AggResult {
  @Field("total_duration") Long duration;
  @Field("avg_duration") Double avgDuration;
}

return template
  .aggregate(aggregation, COLLECTION_NAME, AggResult.class)
  .getUniqueMappedResult()
  .getAvgDuration();

从 Spring 数据 MongoDB 的集合中获取简单平均值

Get simple average from collection with Spring Data MongoDB

aggregate

mongodb

spring-data

spring-data-mongodb