Spring Data MongoDB Aggregate with many fields in _id

Question

I would like to make an aggregate with Spring Data MongoDB and I don't know how to make this group stage :

$group: {
                    _id: {
                        field1: "$field1",
                        field2: "2017-06-21",
                        field3: "$field3"
                    },

                    ...
                }

I don't know how to put the constant date into the second field of the _id

For the moment i do this :

groupOperation = group("field1","field3")

But i'm not sure that it make a group stage on the value of fields and i don't no how put a new field into _id.

I don't find good doc about the operation of different stage of an aggregate in Spring data MongoDB

If someone has an idea I'm interested

Thank you in advance

Answer 1

Here is an example of using multiple fields on group and count the values.

Aggregation aggregate = Aggregation.newAggregation(Aggregation.group("category", "status").count().as("Categoury_Status_Count"));

AggregationResults<String> aggregateResult = mongoOperations.aggregate(aggregate, "category", String.class);

System.out.println(aggregateResult.getMappedResults());

My Sample Data:-

/* 1 */
{
    "_id" : 1,
    "category" : "cafe",
    "status" : "A"
}

/* 2 */
{
    "_id" : 2,
    "category" : "cafe",
    "status" : "B"
}

/* 3 */
{
    "_id" : 3,
    "category" : "cafe1",
    "status" : "A"
}

/* 4 */
{
    "_id" : 4,
    "category" : "cafe1",
    "status" : "B"
}

/* 5 */
{
    "_id" : 5,
    "category" : "cafe1",
    "status" : "B"
}

Output:-

[{ "category" : "cafe1" , "status" : "A" , "Categoury_Status_Count" : 1}, { "category" : "cafe" , "status" : "B" , "Categoury_Status_Count" : 1}, { "category" : "cafe1" , "status" : "B" , "Categoury_Status_Count" : 2}, { "category" : "cafe" , "status" : "A" , "Categoury_Status_Count" : 1}]

To get the _id in the output:-

You can add the _id to the set.

Aggregation aggregate = Aggregation.newAggregation(Aggregation.group("category", "status").count().as("Categoury_Status_Count").addToSet("_id").as("ids"));

Output:-

[{ "category" : "cafe1" , "status" : "A" , "Categoury_Status_Count" : 1 , "ids" : [ 3.0]}, { "category" : "cafe" , "status" : "B" , "Categoury_Status_Count" : 1 , "ids" : [ 2.0]}, { "category" : "cafe1" , "status" : "B" , "Categoury_Status_Count" : 2 , "ids" : [ 5.0 , 4.0]}, { "category" : "cafe" , "status" : "A" , "Categoury_Status_Count" : 1 , "ids" : [ 1.0]}]

Answer 2

Fields fields = Fields.fields("field1", "field2", "field3");
GroupOperation groupOp = Aggregation.group(fields);

This will make group block

$group: {
        _id: {
            field1: "$field1",
            field2: "$field2",
            field3: "$field3"
        }