我是 mongo 的新手。下面是我在 mongodb shell 中执行的聚合操作。但是在我的 java ProjectionAggregation 中，我无法提供 $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);
示例输出
Output in db shell
{
"_id" : ObjectId("5d2f08574de2690001c281ac"),
"username" : "<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="503b2362646110373f3f7e333f3d" rel="noreferrer noopener nofollow">[email protected]</a>",
"beneficiaries" : {
"studentId" : "5d2f0e9c3bcf3e0001a7e562",
"mcBeneficiaryId" : "597418",
"enabled" : true
},
"beneficiaryStudId" : ObjectId("5d2f0e9c3bcf3e0001a7e562"),
"studProfile" : [
{
"_id" : ObjectId("5d2f0e9c3bcf3e0001a7e562"),
"lastName" : "Sharma",
"firstName" : "Kapil",
"studentRegisterCustomFieldValues" : [
{
"bcfdValue" : "One",
"bcfdName" : "Year"
}
],
"gender" : "M",
"merchantId" : "38788943"
}
]
}
如java中那样
如果我将 $toObjectId 添加到上面的 java 聚合投影查询并运行它，则 StudProfile 数组始终为空，它会生成与 db shell 相同的值。
最佳答案
Spring data 不支持少数类型的方法。这个问题可能也包含在其中。但我们可以使用这个解决方案。
Aggregation aggregation=newAggregation(
p-> new Document("$project",
new Document()
.append("username","$username"),
.append("beneficiaries","$beneficiaries)
.append("beneficiaryStudId",
new Document("$toObjectId","$beneficiaries.studentId")
)
)
)
关于java - 如何在Java Mongodb投影操作中给出$ObjectId，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/64953363/