在mongodb聚合中查找

由于您具有嵌套数组，因此需要首先应用

$unwind

$lookup

db.personaddress.aggregate([    { "$unwind": "$address" },    { "$unwind": "$address.location" },    {        "$lookup": { "from": "places",  "localField": "address.location.place._id",  "foreignField": "_id",  "as": "address.location.place",         }    }])

然后可以实现为（未试用）：

LookupOperation lookupOperation = LookupOperation.newLookup()    .from("places")    .localField("address.location.place._id")    .foreignField("_id")    .as("address.location.place");Aggregation agg = newAggregation(    unwind("address"),    unwind("address.location"),    lookupOperation  );AggregationResults<Outputdocument> aggResults = mongoTemplate.aggregate(    agg, PersonAddressdocument.class, Outputdocument.class);

如果您的Spring Data版本不支持此功能，则一种解决方法是实施
AggregationOperation
接口以接受

DBObject

public class CustomGroupOperation implements AggregationOperation {    private DBObject operation;    public CustomGroupOperation (DBObject operation) {        this.operation = operation;    }    @Override    public DBObject toDBObject(AggregationOperationContext context) {        return context.getMappedObject(operation);    }}

然后

$lookup

DBObject lookupOperation = (DBObject)new BasicDBObject(    "$lookup", new BasicDBObject("from", "places")        .append("localField", "address.location.place._id")        .append("foreignField", "_id")        .append("as", "address.location.place")       );

然后可以将其用作：

Aggregation agg = newAggregation(    unwind("address"),    unwind("address.location"),    lookupOperation  );AggregationResults<Outputdocument> aggResults = mongoTemplate.aggregate(    agg, PersonAddressdocument.class, Outputdocument.class);