mongotemplate聚合与条件

Question

我有一个文件看起来像这样的集合:

{
  _id: "545b9fa0dd5318a4285f7ce7",
  owner: "admin",  
  messages: [
    {
      id: "100",
      status: "sent",
      note: ""
    },
    {
      id: "100",
      status: "pending",
      note: ""
    },
    {
      id: "101",
      status: "sent",
      note: ""
    },
    {
      id: "102",
      status: "sent",
      note: ""
    },
    {
      id: "101",
      status: "done",
      note: ""
    }
  ]
}

(这只是一个简短的例子,在我的例子中,子数组非常大)

我需要查询集合并获取特定文档的一些统计信息.所以在这个例子中,如果我查询具有id:"545b9fa0dd5318a4285f7ce7"的doucment,我应该得到这个结果:

{
   sent: 3,
   pending: 1,
   done: 1
}

如何使用spring mongotemplate进行此类聚合？

Answer 1

要做这种事情,您需要$cond聚合框架中的运算符.Spring Data MongoDB还没有这样做,而且常见的$group操作中缺少许多东西,甚至只在其下实现$project.

跟踪任何$cond支持实施的问题在这里:

https://jira.spring.io/browse/DATAMONGO-861

对于世界其他地方,它看起来像这样:

db.collection.aggregate([
    { "$match": { "_id": ObjectId("545b9fa0dd5318a4285f7ce7") } },
    { "$unwind": "$messages" },
    { "$group": {
        "_id": "$_id",
        "sent": {
            "$sum": {
                "$cond": [
                    { "$eq": [ "$mesages.status", "sent" ] },
                    1,
                    0
                ]
            }
        },
        "pending": {
            "$sum": {
                "$cond": [
                    { "$eq": [ "$messages.status", "pending" ] },
                    1,
                    0
                ]
            }
        },
        "done": {
            "$sum": {
                "$cond": [
                    { "$eq": [ "$messages.status", "done" ] },
                    1,
                    0
                ]
            }
        }
    }}
])

要在mongotemplate聚合下使用这种东西,你需要一个扩展聚合操作的类,它可以从DBObject构建:

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,您可以将"$ group"定义为DBObject聚合管道中的一个并实现:

   DBObject myGroup = (DBObject)new BasicDBObject(
        "$group", new BasicDBObject(
            "_id","$_id"
        ).append(
            "sent", new BasicDBObject(
                "$sum", new BasicDBObject(
                    "$cond", new Object[]{
                        new BasicDBObject(
                            "$eq", new Object[]{ "$messages.status", "sent"}
                        ),
                        1,
                        0
                    }
                )
            )
        ).append(
            "pending", new BasicDBObject(
                "$sum", new BasicDBObject(
                    "$cond", new Object[]{
                        new BasicDBObject(
                            "$eq", new Object[]{ "$messages.status", "pending"}
                        ),
                        1,
                        0
                    }
                )
             )
        ).append(
            "done", new BasicDBObject(
                "$sum", new BasicDBObject(
                    "$cond", new Object[]{
                         new BasicDBObject(
                            "$eq", new Object[]{ "$messages.status", "done"}
                         ),
                         1,
                         0
                    }
                 )
            )
        )
     );


   ObjectId myId = new ObjectId("545b9fa0dd5318a4285f7ce7");

   Aggregation aggregation = newAggregation(
           match(Criteria.where("_id").is(myId)),
           unwind("messges"),
           new CustomGroupOperation(myGroup)
   );

这允许您提出一个与上面的shell表示基本相同的管道.

所以现在看来​​,在不支持某些操作和序列的情况下,最好的情况是在AgggregationOperation接口上实现一个类,该类可以提供DBObject,或者从您自己的自定义方法内部构造一个.