春季在项目汇总上使用平均

Question

I have the below query working as intended in mongo:

 db.test.aggregate([{$unwind: "$reports"}, {$project:  {reports: 1, avg: {$avg: "$reports.linesCount"}}}`])

However, I'm unable to convert this into Java via spring. You can't seem to run aggregation functions like avg on a ProjectionOperation, but it is possible on a GroupOperation. There isn't an avg() method at all a ProjectionOperation.

Aggregation aggregation = Aggregation.newAggregation( 
                Aggregation.unwind("$reports"), 
                Aggregation.group(Fields.fields("_id"))
                .avg("reports.linesCount").as("avg"));

Any idea why this might be the case, when it clearly is possible in mongo? Is there some other way to translate my query into Java?

Answer 1

Your query: {reports: 1, avg: {$avg: "$reports.linesCount"}}

aggregates on reports.linesCount field, but your java code is trying to aggregate on .avg("reports.processingTime")

So you might operate on wrong field. Check your query