Question

我想将cropYield除以cropAcres，我的数据格式如下，并且我有1000个。因此，我需要为每个条目获取此cropYield/cropAcres的数组作为数组。这是我的 FarmerCropDataLog 集合。

{
  "_id": "5ce681e14e8e8aec5a7e9ac4",
  "_class": "com.cheruvu.webapp.entity.FarmerCropDataLog",
  "farmerId": "5cdc16214e8e21271cb3af5e",
  "cropData": {
    "cropName": "COTTON",
    "crop": "COTTON",
    "cropAcres": 2,
    "cropYield": 10,
    "cropPrice": 9000
  },
  "villageId": "5b0ed0bd77c8ae9704f65c97",
  "creationTime": "1558610401404",
  "lastUpdated": "1558610996163",
  "state": "ACTIVE"
}

这是我尝试过的。

// I need to fetch all users(farmers) with same VillageId, same crop and which are added in last year.

Criteria criteria = Criteria.where(FarmerCropDataLog.Constants.CROP).is(getComparisonSheet.getCrop().name())
                .and(FarmerCropDataLog.Constants.VILLAGE_ID).is(villageId)
                .and(FarmerCropDataLog.Constants.CREATION_TIME).gte(LAST_YEAR);

MatchOperation matchOperation = Aggregation.match(criteria);   

// then via projection i am getting cropYield and divide it via cropAcres.

ProjectionOperation projectionOperation = Aggregation.project(FarmerCropDataLog.Constants.CROP_YIELD);
ProjectionOperationBuilder builder = new ProjectionOperationBuilder("op1", projectionOperation, null);
builder = builder.divide(FarmerCropDataLog.Constants.CROP_ACRES);
projectionOperation = builder.as(GetYieldComparisonResponse.Constants.MAX_YIELD);

// and at last i am running this operation via following code.
AggregationOptions aggregationOptions = Aggregation.newAggregationOptions().allowDiskUse(true).explain(false)
                .cursor(new BasicDBObject("batchSize", 100)).build();
        Aggregation aggregation = Aggregation.newAggregation(matchOperation,projectionOperation)
                .withOptions(aggregationOptions);
        AggregationResults<GetYieldComparisonResponse> aggregationResults = farmerCropDataLogDAO
                .runAggregation(aggregation, FarmerCropDataLog.class, GetYieldComparisonResponse.class);

由此产生的结果为空。我不明白为什么？

Answer 1

您可以像这样使用$divide聚合函数。根据需要添加更多字段以进行投影，这里我投影了farmerId和相应的产量/英亩值。

db.FarmerCropDataLog.aggregate([
    { $project: { farmerId: 1, 
        yieldPerAcre: { $divide: [ "$cropData.cropYield", "$cropData.cropAcres" ] } } }
])

在MongoDB Spring中将一个字段除以另一个字段

1 个答案: