Spring data Mongodb Aggregation SORT order

Question

My application uses Spring data Mongodb and I am trying to sort the data in descending order inside the embedded document, which is NOT working.

Please refer the below JSON document & Aggregation query:

JSON - Stock document:

{
    "_id" : ObjectId("57c6fd7099275c83e6a5b312"),
    "from" : "China",
    "stockDemandPerItem" : [ 
        {
            "item" : "apples",
            "demand" : 150.0
        }, 
        {
            "item" : "plums",
            "demand" : 200.0
        },
        {
            "item" : "pears",
            "demand" : 250.0
        },
        {
            "item" : "oranges",
            "demand" : 100.0
        }
    ]
}

Spring Data Mongodb Aggregation query:

TypedAggregation<Stock> typedAggr =  
         newAggregation(Stock.class, unwind("stockDemandPerItem"),
         project("stockDemandPerItem.item",
         "stockDemandPerItem.demand"),
          sort(Direction.DESC, "stockDemandPerItem.demand"),
            limit(3));

AggregationResults<StockDemandPerItem> results = mongoTemplate.
   aggregate(typedAggr, StockDemandPerItem.class);

List<StockDemandPerItem> list = results.getMappedResults();

for(StockDemandPerItem stockDemandPerItem : list) {
      System.out.println(stockDemandPerItem.getItem() + 
      " :: " +    stockDemandPerItem.getDemand());
}

Current Output:

apples :: 150.0

plums :: 200.0

oranges :: 500.0

Expected Output (desc order by demand):

oranges :: 500.0

plums :: 200.0

apples :: 150.0

Could you please help to get the expected output in descending order ?

Also, I am planning to find the maximum 'demand' value by using the above query with limit(1) & Sort-Direction.DESC. Or else is there any other better approach to get the maximum 'demand' value ?

could you please post your Stock.java ?

alexbt
– alexbt

2016-09-19 10:00:39 +00:00
Commented Sep 19, 2016 at 10:00 — alexbt
– alexbt, Commented Sep 19, 2016 at 10:00

inaitgaJ · Accepted Answer · 2016-10-03 01:17:47Z

-1

We can achieve this using Collection sort in java.

Edit class StockDemandPerItem like so:

public class StockDemandPerItem implements Comparable<StockDemandPerItem>{

//existing code goes here
@Override
public int compareTo(StockDemandPerItem compareStockDemand) {
    //descending order
    return compareStockDemand.getDemand().compareTo(this.getDemand());
   } 
}

Also add this line of code before print loop-

Collections.sort(list);

answered Oct 3, 2016 at 1:17

inaitgaJ

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