Projection to child's field

Question

Spring 1.3.6, using spring-data mongodb

Have a document like this:

{
  "name":"Dmitry",
  "props":{
    "city":"Moscow"
    "age":"26"
  }
}

Want something like this via spring mongo projection

{
  "city":"Moscow",
  "person":{
    "name":"Dmitry",
    "age":"26"
   }
}

Tried this aggregation operations

Aggregation aggregation = newAggregation(
    project().and("name").as("person.name")
        .and("props.city").as("city")
        .and("props.age").as("person.age")
);
AggregationResults<DBObject> results = this.mongoTemplate.aggregate(aggregation, MyType.class, DBObject.class);
results.getMappedResults();

Have a result like this

{
  "city":"Moscow",
  "name":"Dmitry",
  "person":{  
    "age":"26"
   }
}

It is ok to bind field as field with another name, to bind child field to parent field, to bind child field to another child, but I haven't succeed on binding parent field to child via mongo projection.

Answer 1

Here is the Spring code using projection. You may need to replace this code "getMongoConnection()" based on how you get MongoOperations object from Spring context.

Aggregate method using projection:-

public Boolean aggregateMyTypeCollectionUsingProject() {

        MongoOperations mongoOperations = getMongoConnection();

        ProjectionOperation  project = Aggregation.project().and("props.city").as("city").and("props.age").as("person.age").andExpression("name")
                .as("person.name");
        Aggregation aggregate = Aggregation.newAggregation(project);

        System.out.println(aggregate.toString());
        AggregationResults<DBObject> results = mongoOperations.aggregate(aggregate, MyType.class, DBObject.class);

        System.out.println("Result ============>" + results.getMappedResults());
        return true;

    }

My getMongoConnection() method:-

@SuppressWarnings("resource")
public MongoOperations getMongoConnection() {

    return (MongoOperations) new AnnotationConfigApplicationContext(SpringMongoConfig.class)
            .getBean("mongoTemplate");
}

Query:-

{ "aggregate" : "__collection__" , "pipeline" : [ { "$project" : { "city" : "$props.city" , "person.age" : "$props.age" , "person.name" : "$name"}}]}

Output:-

{
    "_id": {
        "$oid": "57b32d31ced49443e4b79f0d"
    },
    "city": "Moscow",
    "person": {
        "age": "26",
        "name": "Dmitry"
    }
}