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Lookup aggregation in mongoDB using groovy in Jmeter


By : Ramdani Ahmad
Date : October 14 2020, 02:21 PM
this will help Your syntax is not compatible with Groovy GStrings, as per documentation:
code :
assert '${name}' == "\${name}"
DBObject lookup = new BasicDBObject('$lookup', lookupFields);  
DBObject lookup = new BasicDBObject("\$lookup", lookupFields);  


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Is it possible to do a $lookup aggregation between two databases in Mongodb?


By : adam
Date : March 29 2020, 07:55 AM
I hope this helps .
Is it possible to do a $lookup aggregation between two databases in Mongodb?
code :
{
   $lookup:
     {
       from: <collection to join>,
       localField: <field from the input documents>,
       foreignField: <field from the documents of the "from" collection>,
       as: <output array field>
     }
}
db.getSiblingDB('test').foo.find()

lookup in mongodb aggregation


By : Yakup
Date : March 29 2020, 07:55 AM
Does that help Since you have nested arrays, you need to apply the $unwind operator first in order to denormalise the embedded documents before using the $lookup pipeline (unless you have already flattened them in your aggregation operation):
code :
db.personaddress.aggregate([
    { "$unwind": "$address" },
    { "$unwind": "$address.location" },
    {
        "$lookup": {
            "from": "places", 
            "localField": "address.location.place._id", 
            "foreignField": "_id", 
            "as": "address.location.place", 
        }
    }
])
LookupOperation lookupOperation = LookupOperation.newLookup()
    .from("places")
    .localField("address.location.place._id")
    .foreignField("_id")
    .as("address.location.place");

Aggregation agg = newAggregation(
    unwind("address"),
    unwind("address.location"),
    lookupOperation  
);

AggregationResults<OutputDocument> aggResults = mongoTemplate.aggregate(
    agg, PersonAddressDocument.class, OutputDocument.class
);
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);
    }
}
DBObject lookupOperation = (DBObject)new BasicDBObject(
    "$lookup", new BasicDBObject("from", "places")
        .append("localField", "address.location.place._id")
        .append("foreignField", "_id")
        .append("as", "address.location.place")       
);
Aggregation agg = newAggregation(
    unwind("address"),
    unwind("address.location"),
    lookupOperation  
);

AggregationResults<OutputDocument> aggResults = mongoTemplate.aggregate(
    agg, PersonAddressDocument.class, OutputDocument.class
);

MongoDB aggregation lookup


By : Olivier La
Date : March 29 2020, 07:55 AM
wish help you to fix your issue I would like to aggregate building with floors and rooms: , $unwind makes floors $lookupable and $group adds them together again.
code :
db.getCollection('buildings').aggregate([
    {
        "$lookup": {
            "from": "floors",
            "localField": "_id",
            "foreignField": "buildingId",
            "as": "floors"
        }
    },
    {
        "$unwind": "$floors"
    },
    {
        "$lookup": {
            "from": "rooms",
            "localField": "floors._id",
            "foreignField": "floorId",
            "as": "floors.rooms"
        }
    },
    {
        "$group": {
            "_id": "$_id",
            "name": { "$first": "$name" },
            "floors": { "$push": "$floors" }
        }
    }]);

mongodb - How to access lookup results in another lookup in aggregation?


By : Deepali
Date : March 29 2020, 07:55 AM
wish help you to fix your issue Use $arrayElemAt to access the element from previous lookup array.
Try
code :
let: {elem: {$arrayElemAt:["$sales_agent", 0]}} 
{$match: {$expr: {$eq: ['$_id', '$$elem.office']}}}
let: {office: {$let:{vars:{elem:{$arrayElemAt:["$sales_agent", 0]}}, in:"$$elem.office"}}}

Perform Mongodb Aggregation in JMeter


By : Akhil_Buddha
Date : March 29 2020, 07:55 AM
I wish this help you Collection.aggregate() function call returns AggregateIterable which cannot be cast to the document directly, you can use Groovy head() method which returns the first value from the Iterable instance like:
code :
Document result = collection.aggregate(Arrays.asList(Aggregates.sample(1))).head()
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