使用Java的Mongo 3.2驱动程序的新聚合function

我想在Mongo 3.2中执行聚合，如此处所述，但在Java中：

https://docs.mongodb.org/master/reference/operator/aggregation/lookup/#pipe._S_lookup

目前我在java中的查询对象非常简单：

Document query = new Document(); query.append("employeId", employeId); 

除了通过employeId过滤，我想加入这个集合与公司（其中employee.company_id = company.id）

我怎么能用Java做到这一点？ 好像我找不到这个新的Mongofunction的文档。

编辑

员工收集示例：

 { "id" : 1, "name" : "John", "lastName" : "Moore", "age" : 44, "companyId": 10 } 

公司集合示例：

 { "id" : 10, "companyName" : "Microsoft", "numEmployee" : 100 } 

预期输出的示例

 { "id" : 1, "name" : "John", "lastName" : "Moore", "companyId" : 10, "companyName" : "Microsoft" } 

Answer 1

运行以下聚合管道应该为您提供所需的结果

 pipeline = [ { "$match": { "_id": employeeId } }, { "$lookup": { "from": "company", "localField": "companyId", "foreignField": "_id", "as": "company" } }, { "$project": { "name": 1, "lastName": 1, "companyId": 1, "companyName": "$company.companyName" } } ]; db.employee.aggregate(pipeline); 

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Java测试实现

 public class JavaAggregation { public static void main(String args[]) throws UnknownHostException { MongoClient mongo = new MongoClient(); DB db = mongo.getDB("test"); DBCollection coll = db.getCollection("employee"); // create the pipeline operations, first with the $match DBObject match = new BasicDBObject("$match", new BasicDBObject("_id", employeeId) ); // build the $lookup operations DBObject lookupFields = new BasicDBObject("from", "company"); lookupFields.put("localField", "companyId"); lookupFields.put("foreignField", "_id"); lookupFields.put("as", "company"); DBObject lookup = new BasicDBObject("$lookup", lookupFields); // build the $project operations DBObject projectFields = new BasicDBObject("name", 1); projectFields.put("lastName", 1); projectFields.put("companyId", 1); projectFields.put("companyName", "$company.companyName"); DBObject project = new BasicDBObject("$project", projectFields); List pipeline = Arrays.asList(match, lookup, project); AggregationOutput output = coll.aggregate(pipeline); for (DBObject result : output.results()) { System.out.println(result); } } }