在spring boot中使用mongodb从两个集合中获取数据

Question

There are two collections in the below query(users and department). I am able to get the data in mongo cell but when I tried with java code than got only one collection of data.

db.users.aggregate([
  {
  "$lookup":{
     "from":"department",
     "localField":"user_department_id",
     "foreignField":"department_id"
    }
   ]);

Basically, I just want to convert to a java project. where using mongo template in spring-boot.

This is the service. I always get users' data while requiring both collection data.

public class UsersService {

@Autowired
private MongoTemplate mongoTemplate;

public void lookupOperation(){
LookupOperation lookupOperation = LookupOperation.newLookup()
                    .from("department")
                    .localField("user_department_id")
                    .foreignField("department_id")
                    .as("departments");

Aggregation aggregation = Aggregation.newAggregation(lookupOperation);
    List<UsersDeptResult> results = mongoTemplate.aggregate(aggregation, "department", users.class).getMappedResults();
   
}

}

Answer 1

You can simply use

@Autowired
private MongoTemplate mongoTemplate;

public List<YOUR_CONVERTER_CLASS> test() {

    Aggregation aggregation = Aggregation.newAggregation(   
        lookup("department","user_department_id","department_id","departments")
    ).withOptions(AggregationOptions.builder().allowDiskUse(Boolean.TRUE).build());

    return mongoTemplate.aggregate(aggregation, mongoTemplate.getCollectionName(YOUR_COLLECTION.class), YOUR_CONVERTER_CLASS.class).getMappedResults();

}