Spring MongoDB distict - can't get full document - spring

Question

I have collection in following format.
{
id:____,
name:"Carlos",
city:"Mumbai"
},
{
id:____,
name:"Pravin",
city:"Mumbai"
},
{
id:_____,
name:"Gaurav",
city:"Ahmedabad"
}
I want whole document distinct by city. I tried the db.collection.distinct("city"). But it returns only distinct cities.
Current Output:
["Mumbai","Ahmedabad"]
Expected Output:
{
id:____,
name:"Carlos",
city:"Mumbai"
},
{
id:_____,
name:"Gaurav",
city:"Ahmedabad"
}
Above you can see there is only one record of "Mumbai". I need this kind of output.
Anyone know how we can get whole document with distinct in spring-mongodb?

Answer 1

You could try running an aggregation pipeline operation where you can include the the other fields inside the $group pipeline stage using the $first operator. Two examples that show this approach follow:
Mongo Shell:
pipeline = [
{
"$group": {
"_id": "$city",
"id": { "$first": "$_id" },
"name": { "$first": "$name" }
}
}
]
db.collection.aggregate(pipeline);
Spring Data MongoDB:
import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
MongoTemplate mongoTemplate = repository.getMongoTemplate();
Aggregation agg = newAggregation(
group("city")
.first("_id").as("id")
.first("name").as("name")
);
AggregationResults<OutputType> result = mongoTemplate.aggregate(agg,
"collection", OutputType.class);
List<OutputType> mappedResult = result.getMappedResults();