Java Syntax for a Mongo Aggregation Query

Question

I have got stuck with the Java syntax for a Mongo query.

I have written the Mongo query for console but I want the corresponding Java syntax for that query.

Here's the shell command:

db.errorsegmentaudit.aggregate([
    {$sort:{timestamp:1}},
    {$limit:1},
    {$unwind:"$auditErrorTypeCounts"},
    {$unwind:"$auditErrorTypeCounts.auditErrorCounts"}, 
    {$group: {
            _id: {
                "agent": "$auditErrorTypeCounts.auditErrorCounts.agentName", 
                "type":"$auditErrorTypeCounts.typeOfError"
            }, 
            count: {
                $sum: "$auditErrorTypeCounts.auditErrorCounts.countOfErrors"
            }
        }    
    } 
])

I have gone through the documentation and all but didn't find the right one. I tried using Aggregation class in Java but it didn't work.

Answer 1

The MongoDB Java driver (using version 3.x) equivalent of the MongoDB shell command in your question is:

MongoClient mongoClient = ...;

MongoCollection<Document> collection = mongoClient.getDatabase("...").getCollection("..");

AggregateIterable<Document> documents = collection.aggregate(Arrays.asList(
        // $sort:{timestamp:1}
        Aggregates.sort(Sorts.ascending("timestamp")),

        // $limit:1
        Aggregates.limit(1),

        // $unwind:"$auditErrorTypeCounts"
        Aggregates.unwind("$auditErrorTypeCounts"),

        // $unwind:"$auditErrorTypeCounts.auditErrorCounts"
        Aggregates.unwind("$auditErrorTypeCounts.auditErrorCounts"),

        // $group:{...}
        Aggregates.group(
                // _id:{"agent":"$auditErrorTypeCounts.auditErrorCounts.agentName","type":"$auditErrorTypeCounts.typeOfError"}
                new Document("agent", "$auditErrorTypeCounts.auditErrorCounts.agentName").append("type", "$auditErrorTypeCounts.typeOfError"),

                // count:{$sum:"$auditErrorTypeCounts.auditErrorCounts.countOfErrors"}}}
                Accumulators.sum("count", "$auditErrorTypeCounts.auditErrorCounts.countOfErrors")
        )
));

The comments above each stage in the aggregation pipeline show which shell command the Java code mirrors. For example:

// $unwind:"$auditErrorTypeCounts.auditErrorCounts"
Aggregates.unwind("$auditErrorTypeCounts.auditErrorCounts")

... shows you that the Java equivalent to the shell command $unwind:"$auditErrorTypeCounts.auditErrorCounts" is Aggregates.unwind("$auditErrorTypeCounts.auditErrorCounts"). This may make it easier for you to map one to the other.

More details in the MongoDB Java driver docs.