Spring Data MongoDb 是否支持 $filter 数组聚合运算符？

Question

I'm trying to implement in Spring Data using MongoTemplate the following working mongoDb query:

db.answers.aggregate([
        { "$match" : { "object_id" : "1" } },
        { "$project": { 'answer_list': 1, 'profile': { $filter : { input: '$answer_list', as: 'answer', cond: { $eq: [ '$$answer.question', 2 ] } } } } },
        { "$unwind" : "$profile"},
        { "$unwind" : "$answer_list"},
        { "$group" : { "_id" : { "question" : "$answer_list.question", "answer" : "$answer_list.answer", "criteria" : "$profile.answer"}, "count" : { "$sum" : 1 } } },
        { "$sort" : { "_id.question" : 1, "_id.answer" : 1 } }
]);

The collection has this structure:

{
"_id" : ObjectId("..."),
"object_id" : ObjectId("..."),
"answer_list" : [ 
    {
        "question" : NumberLong(0),
        "answer" : NumberLong(0)
    }, 
    {
        "question" : NumberLong(1),
        "answer" : NumberLong(2)
    }, 
    {
        "question" : NumberLong(2),
        "answer" : NumberLong(2)
    }
]}

What I'm trying to do here is a report on a simple survey submission data. The question is "How did the users that answered 0 to the first question answer to the second question?" I spent all day searching the SpringData Mongo Db docs but I found nothing. Can anyone help?

TIA

Answer 1

You can workaround this issue by providing your own AggregationExpression .

ProjectionOperation agg = Aggregation.project() //

      .and(new AggregationExpression() {

        @Override
        public DBObject toDbObject(AggregationOperationContext context) {

          DBObject filterExpression = new BasicDBObject();
          filterExpression.put("input", "$answer_list");
          filterExpression.put("as", "answer");
          filterExpression.put("cond", new BasicDBObject("$eq2", Arrays.<Object> asList("$$answer.question", 2)));

          return new BasicDBObject("$filter", filterExpression);
        }
      }).as("profile");

Answer 2

There is one more alternative using Aggregation

Aggregation aggregation = newAggregation(
                           project()
                           .and(filter("answer_list")
                           .as("answer")
                       .by(valueOf("answer.question").equalToValue(2)))
                           .as("profile"));
AggregationResults<OutputType> profile = mongoTemplate.aggregate(aggregation, InputType.class, OutputType.class);

I may not be able to answer your question correctly but I just wanted to give another approach for aggregation as there are lesser number of examples using Aggregation .

In project() you can specify keys you want in your response, as its a varargs method