如何使用Spring数据投影数组字段

Question

我正在尝试使用Spring Data MongoDB创建一个聚合管道，该管道将新的数组字段投射到管道中。如何使用Spring Data实现这一目标？

我试图复制的Pipeline阶段如下：

{
    $project: {
        "aceId": 1,     
        "startActivityDateTime": 1,
        "lastActivityDateTime": 1, 
        "eventInfo": [ 
            "$applicationInfo", 
            "$riskAssessmentInfo", 
            "$policyInfo", 
            "$submissionInfo"
        ] 
    }
},

Answer 1

我遇到了同样的问题并找到了解决方案。你必须创建一个CustomAggregationOperation类，如下所示： https://stackoverflow.com/a/29186539/5033846

public class CustomProjectAggregationOperation implements AggregationOperation {
    private DBObject operation;

    public CustomProjectAggregationOperation (DBObject operation) {
        this.operation = operation;
    }

    @Override
    public DBObject toDBObject(AggregationOperationContext context) {
        return context.getMappedObject(operation);
    }

}

然后您可以按如下方式实现投影阶段：

new CustomAggregationOperation(new BasicDBObject("$project",
    new BasicDBObject("aceId", 1)
      .appending("startActivityDateTime", 1)
      .appending("lastActivityDateTime", 1)
      .appending("eventInfo", 
         new Object[]{
           "$applicationInfo", 
           "$riskAssessmentInfo", 
           "$policyInfo", 
           "$submissionInfo"}
       )
));