如何在Java Mongo投影操作中给出$toObjectId

我是蒙哥的新蜜蜂。下面是我在

mongodb

shell中执行的聚合操作。但是在我的java ProjectionAggregation中，我无法给出

$toObjectId

。请纠正我遗漏了什么

db shell查询

 db.getCollection('UserData').aggregate([

{
 $project : {
     "username" : "$username",
     "beneficiaries" : "$beneficiaries"
        
     }   
 },
 {
    $unwind :   {
        path : "$beneficiaries",
        preserveNullAndEmptyArrays: true
    }
  },
  {
 $project : {  
     "username" : "$username",
     "beneficiaries" : "$beneficiaries",
      ---- dont know how to give $toObjectId in java ProjectionOperation .
     "beneficiaryStudId" : { $toObjectId : "$beneficiaries.studentId" }  
     }
 },
  {
      $lookup:
         {
           from: "StudentProfileData",
           localField: "beneficiaryStudId",
           foreignField: "_id",
           as: "studProfile"
          }
      }
])

Java代码投影操作

        ProjectionOperation projectUserAndBeneficiaries = Aggregation.project()
                  .andExpression("username").as("username")
                  .andExpression("beneficiaries").as("beneficiaries");

        
        ProjectionOperation projectUserAndOtherDetails = Aggregation.project()
                  .andExpression("username").as("username")
                  .andExpression("beneficiaries").as("beneficiaries")
---- How to give $toObjectId in projection operation             .andExpression("beneficiaries.studentId").as("beneficiaryStudId");
                  
        LookupOperation lookupOperation = LookupOperation.newLookup().
                from("StudentProfileData").
                localField("beneficiaryStudId").
                foreignField("_id").
                as("studProfile");
 
        Aggregation agg = Aggregation.newAggregation(projectUserAndBeneficiaries, unwindBeneficiars,  
                projectUserAndOtherDetails
                ,lookupOperation);
        AggregationResults<UserAndStudentData> output 
          = mongotemplate.aggregate(agg, "UserData", UserAndStudentData.class);

      

其中如java

---

如果我在上面的java聚合投影查询中添加$toObjectId并运行它，则studProfile数组始终为空。它生成的值与db shell的值相同。

Spring数据不支持几种类型的方法。这个问题可能包括在内。但是我们可以使用这个解决方案

Aggregation aggregation=newAggregation(
    p-> new Document("$project",
        new Document()
        .append("username","$username"),
        .append("beneficiaries","$beneficiaries)
        .append("beneficiaryStudId",
            new Document("$toObjectId","$beneficiaries.studentId")
        )
     )
 )

---

对不起，如果我在工作，你能纠正我吗。您希望在问题中添加预期的输出@明斯基不懂java，但它从atlas导出到这个

Arrays.asList（project（computed（“username”）、“$username”）、computed（“受益人”、“受益人”）、computed（“受益人研究”、eq（“toObjectId”）、“$受益人.studentId”））

Aggregation aggregation=newAggregation(
    p-> new Document("$project",
        new Document()
        .append("username","$username"),
        .append("beneficiaries","$beneficiaries)
        .append("beneficiaryStudId",
            new Document("$toObjectId","$beneficiaries.studentId")
        )
     )
 )