如何在字符串中使用json执行聚合mongo查询? [英] How to perform an aggregate mongo-query using json in a String?

问题描述

我有一个用于mongodb的带有汇总json查询(从文件加载)的字符串.在robomongo中，它运作良好.所以在robomongo中，我有:

I have a string with an aggregate json query (loaded from a file) for mongodb. In robomongo, it works well. So in robomongo, I have:

db.getCollection('Odds').aggregate(
[
{
     "$lookup": {
        "from": "...",
        "localField": "...",
        "foreignField": "...",
        "as": "..."
     }
},
{    "$unwind": "$..." },
{
     "$redact": {
         ... etc ...
     }
}
]
)

json文件是一样的，只是删除了第一行和最后一行，所以它是json.当我在Java中加载它时，它可以正确解析.解析的结果恰好是"BasicDBList":

The json file is just the same but with the first and the last line removed so that it's json. When I load this in Java, it parses correctly. The result of the parse happens to be a "BasicDBList":

String query = "..."; // read from file
BasicDBList q = (BasicDBList) JSON.parse(query);

现在，我正在尝试将其传递给聚合函数，但是它不起作用:

Now, I'm trying to pass this to the aggregate function, but it doesn't work:

new MongoClient().getDatabase("db").getCollection("coll").aggregate(q);

该行给出:

The method aggregate(List<? extends Bson>) in the type MongoCollection<Document> is not applicable for the arguments (BasicDBList)

是否有一种转换类型的方法?我应该用其他方式吗?

Is there a way to convert the types? Should I do it in another way?

推荐答案

您距离解决方案不远:

聚合函数采用:.aggregate(List<DBObject>) 但是，如果您的查询中有列表，则要使用的JSON.parse可以让您进行类型转换，因此没有问题

The aggregate function takes: .aggregate(List<DBObject>) But the JSON.parse you want to use lets you typecast into it, if you have a list in your query, so no Problem

String query="[....}";
List<DBObject> q= (List<DBObject>)JSON.parse(query);
Iterable<DBObject> result=new MongoClient().getDatabase("db").getCollection("coll").aggregate(q).results();`

然后可以迭代结果.

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