Count number of documents using Aggregation MongoDB

Question

I have mongo documents roughly like

{
    "_id": {
              "$oid": "243234"
    },
    "category": ["cat1", "cat2"]
}

want to get the count of all the category, (i.e, cat1 = 20, cat2 = 7)
Numbers 20 and 7 are the number of documents where the category list contains respective elements.

Tried aggregation in mongoTemplate which I don't quite get the required projected result.

The projection model:

public class CountModel{
    private String category;
    private Integer count;
}

The code I have tried:

GroupOperation categoryGroup = group("category").count().as("categoryCount");

ProjectionOperation projectionToModel = project()
   .andExpression("category").as("category")
   .andExpression("categoryCount").as("count");

Aggregation aggregation = newAggregation(categoryGroup, matchOperation, projectionToModel);

AggregationResults<PIICategoryCount> results = mongoTemplate.aggregate(aggregation,
   "repo_name",
    CountModel.class);
return results.getMappedResults();

R2D2 · Accepted Answer · 2021-01-04 09:37:06Z

1

     db.collection.aggregate([ {$unwind:"$category"}   , { $group:{ _id:"$category" , count: { $sum:1}}   } ])

answered Jan 4, 2021 at 9:37

R2D2

10.9k2 gold badges20 silver badges41 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Siva Rahul · Accepted Answer · 2021-01-04 10:49:34Z

Thank you @kiko075 for the answer.

Just giving the answer in spring boot acceptable form.

// unwinds the document(have each document for each element in the list)
UnwindOperation unwindOperation = Aggregation.unwind("category");

// groups by the category which was unwound and counted
GroupOperation categoryGroup = Aggregation.group("category").count().as("categoryCount");

ProjectionOperation projectionToModel = project()
                    .andExpression("_id").as("category")         // _id refers to the unwound category (i.e, cat1)
                    .andExpression("categoryCount").as("count");

Aggregation aggregation = Aggregation.newAggregation(unwindOperation, categoryGroup, projectionToModel);

AggregationResults<CountModel> results = mongoTemplate.aggregate(aggregation,
                    "repo_name",
                    CountModel.class);
return results.getMappedResults();

Collectives™ on Stack Overflow

Count number of documents using Aggregation MongoDB

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related