How to perform an aggregate mongo-query using json in a String?

Question

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 ...
     }
}
]
)

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);

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

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

That line gives:

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

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

ARMistice · Accepted Answer · 2016-10-07 17:17:09Z

1

You are not far from the solution:

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();`

The results can than be iterated.

answered Oct 7, 2016 at 17:17

ARMistice

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