如何在mgo bson中聚合字段类型map [string] uint32？

I am trying to get aggregated values from a mongo collection using bson and Golang where the field used in Golang is of type map[string]uint32.

This is the struct am using and the field is Csat.

type Conversations struct {
     ID   bson.ObjectId     `bson:"_id"`
     Csat map[string]uint32 `bson:"csat"`

}

The output using bson should be in key value pairs, these are some examples I tried but did not work,

1.

bson.M{

    "csat["1"]": bson.M{
        "$sum": bson.M{"$cond": []interface{}{bson.M{"$eq": []interface{}{"$score", 1}}, 1, 0}},
    },
    "csat["2"]": bson.M{
        "$sum": bson.M{"$cond": []interface{}{bson.M{"$eq": []interface{}{"$score", 2}}, 1, 0}},
    }

2.

bson.M{
        "csat": bson.M{
            "1": bson.M{
                "$sum": bson.M{"$cond": []interface{}{bson.M{"$eq": []interface{}{"$score", 1}}, 1, 0}},
            },
            "2": bson.M{
                "$sum": bson.M{"$cond": []interface{}{bson.M{"$eq": []interface{}{"$score", 2}}, 1, 0}},
            },
        }
    }

I expect it to store it like {"csat": {"1": 3}, {"2": 2}, ...} where 3 and 2 could be values of the keys.

If anyone has done something like this before, can you please help me out?

Thanks.