Question

我正在使用带有Spring Data的MongoDB（3.4）。当我使用查找操作时，我得到的结果不正确。收集操作如下：

@Document
public class Employee {
    @Id
    String id;
    String name;
    @DBRef
    EmpAddress address;

    String city;     //redundant, but intentionally 
    //getters and setters
}

@Document
public class EmpAddress {
    @Id
    String id;

    String city;
    //getters and setters
}

DB填充了以下数据

Employees [{ "_id" : { "$oid" : "597b557cfe4b9104e8409f2a"} , "_class" : "com.example.Employee" , "name" : "PKM1" , "city" : "NYC" , "address" : { "$ref" : "empAddress" , "$id" : { "$oid" : "597b557bfe4b9104e8409f25"}}}, { "_id" : { "$oid" : "597b557cfe4b9104e8409f2b"} , "_class" : "com.example.Employee" , "name" : "PKM2" , "city" : "SFO" , "address" : { "$ref" : "empAddress" , "$id" : { "$oid" : "597b557bfe4b9104e8409f26"}}}, { "_id" : { "$oid" : "597b557cfe4b9104e8409f2c"} , "_class" : "com.example.Employee" , "name" : "PKM3" , "city" : "LA" , "address" : { "$ref" : "empAddress" , "$id" : { "$oid" : "597b557bfe4b9104e8409f27"}}}, { "_id" : { "$oid" : "597b557cfe4b9104e8409f2d"} , "_class" : "com.example.Employee" , "name" : "PKM4" , "city" : "SFO" , "address" : { "$ref" : "empAddress" , "$id" : { "$oid" : "597b557bfe4b9104e8409f28"}}}, { "_id" : { "$oid" : "597b557cfe4b9104e8409f2e"} , "_class" : "com.example.Employee" , "name" : "PKM5" , "city" : "NYC" , "address" : { "$ref" : "empAddress" , "$id" : { "$oid" : "597b557bfe4b9104e8409f29"}}}]



Cities [{ "_id" : { "$oid" : "597b557bfe4b9104e8409f25"} , "_class" : "com.example.EmpAddress" , "city" : "NYC"}, { "_id" : { "$oid" : "597b557bfe4b9104e8409f26"} , "_class" : "com.example.EmpAddress" , "city" : "SFO"}, { "_id" : { "$oid" : "597b557bfe4b9104e8409f27"} , "_class" : "com.example.EmpAddress" , "city" : "LA"}, { "_id" : { "$oid" : "597b557bfe4b9104e8409f28"} , "_class" : "com.example.EmpAddress" , "city" : "SFO"}, { "_id" : { "$oid" : "597b557bfe4b9104e8409f29"} , "_class" : "com.example.EmpAddress" , "city" : "NYC"}]

当我按如下方式查询时

MatchOperation match = Aggregation.match(Criteria.where("name").is("PKM1"));
LookupOperation lookup = LookupOperation.newLookup().from("empAddress").localField("address.$id").foreignField("id").as("emp_loc");
Aggregation aggregation = Aggregation.newAggregation(match, lookup);
AggregationResults<DBObject> result = mongoTemplate.aggregate(aggregation, "employee", DBObject.class);

结果是：

[{ "_id" : { "$oid" : "597b557cfe4b9104e8409f2a"} , "_class" : "com.example.Employee" , "name" : "PKM1" , "city" : "NYC" , "address" : { "$ref" : "empAddress" , "$id" : { "$oid" : "597b557bfe4b9104e8409f25"}} , "emp_loc" : [ { "_id" : { "$oid" : "597b557bfe4b9104e8409f25"} , "_class" : "com.example.EmpAddress" , "city" : "NYC"} , { "_id" : { "$oid" : "597b557bfe4b9104e8409f26"} , "_class" : "com.example.EmpAddress" , "city" : "SFO"} , { "_id" : { "$oid" : "597b557bfe4b9104e8409f27"} , "_class" : "com.example.EmpAddress" , "city" : "LA"} , { "_id" : { "$oid" : "597b557bfe4b9104e8409f28"} , "_class" : "com.example.EmpAddress" , "city" : "SFO"} , { "_id" : { "$oid" : "597b557bfe4b9104e8409f29"} , "_class" : "com.example.EmpAddress" , "city" : "NYC"}]}]

上述结果不正确，因为所有城市都已上市。

但是，如果我在另一个字段上查找，我会得到正确的结果

LookupOperation lookup = LookupOperation.newLookup().from("empAddress").localField("city").foreignField("city").as("emp_loc");

结果如下：

[{ "_id" : { "$oid" : "597b557cfe4b9104e8409f2a"} , "_class" : "com.example.Employee" , "name" : "PKM1" , "city" : "NYC" , "address" : { "$ref" : "empAddress" , "$id" : { "$oid" : "597b557bfe4b9104e8409f25"}} , "emp_loc" : [ { "_id" : { "$oid" : "597b557bfe4b9104e8409f25"} , "_class" : "com.example.EmpAddress" , "city" : "NYC"} , { "_id" : { "$oid" : "597b557bfe4b9104e8409f29"} , "_class" : "com.example.EmpAddress" , "city" : "NYC"}]}]

当我使用id查找时，如何获得第二个结果？

Answer 1

来自DBref的问题。从mongoDB 3.4开始，不能在聚合管道中使用DBRef，除非在$ match阶段。

查询返回所有结果，因为id为null，我遇到了同样的问题。

您应该创建手动引用以防止出现此问题。

您可以在此答案中详细了解此信息：https://stackoverflow.com/a/41677055/4023844

用dbref弹出数据mongodb查找

1 个答案: