Spring data Match and Filter Nested Array

Question

How can extract data from nested array ?

I want to extract the array item \"values\" where wind_speed parameter value is between vitRange.min and vitRange.max (same

Answer 1

I'm just going to hardcode some values here to match the "first" array index of "polaire" and the "second" array index of "matrice" for demonstration. Note here the usage of $elemMatch in the $match aggregation pipeline stage and the usage of $map and $filter in the $project pipeline stage:

Aggregation aggregation = newAggregation(
  match(
    Criteria.where("name").is("race").and("polaire").elemMatch(
      Criteria.where("voile").is("foc")
        .and("matrice").elemMatch(
          Criteria.where("vitRange.min").lt(5)
            .and("vitRange.max").gt(5)
            .and("twaRange.min").lt(32)
            .and("twaRange.max").gt(32)
        )
    )
  ),
  project("name")
    .and(new AggregationExpression() {
      @Override
      public DBObject toDbObject(AggregationOperationContext context) {
        return new BasicDBObject("$map",
          new BasicDBObject("input",new BasicDBObject(
            "$filter", new BasicDBObject(
              "input", "$polaire")
              .append("as","p")
              .append("cond", new BasicDBObject("$eq", Arrays.asList("$$p.voile","foc")))
          ))
          .append("as","p")
          .append("in", new BasicDBObject(
            "voile", "$$p.voile")
            .append("matrice",new BasicDBObject(
              "$filter", new BasicDBObject(
                "input", "$$p.matrice")
                .append("as","m")
                .append("cond", new BasicDBObject(
                  "$and", Arrays.asList(
                    new BasicDBObject("$lt", Arrays.asList("$$m.vitRange.min", 5)),
                    new BasicDBObject("$gt", Arrays.asList("$$m.vitRange.max", 5)),
                    new BasicDBObject("$lt", Arrays.asList("$$m.twaRange.min", 32)),
                    new BasicDBObject("$gt", Arrays.asList("$$m.twaRange.max", 32))
                  )
                ))
            ))
          )
        );
      }
    }).as("polaire")
);

Which translates to this serialization:

[
  { "$match": {
    "name": "race",
    "polaire": {
      "$elemMatch": {
        "voile": "foc",
        "matrice": {
          "$elemMatch": {
            "vitRange.min": { "$lt": 5 },
            "vitRange.max": { "$gt": 5 },
            "twaRange.min": { "$lt": 32 },
            "twaRange.max": { "$gt": 32 }
          }
        }
      }
    }
  }},
  { "$project": {
    "name": 1,
    "polaire": {
       "$map": {
         "input": {
           "$filter": {
             "input": "$polaire",
             "as": "p",
             "cond": { "$eq": [ "$$p.voile", "foc" ] }
           } 
         },
         "as": "p",
         "in": {
           "voile": "$$p.voile",
           "matrice": {
             "$filter": {
               "input": "$$p.matrice",
               "as": "m",
               "cond": {
                 "$and": [
                   { "$lt": [ "$$m.vitRange.min", 5 ] },
                   { "$gt": [ "$$m.vitRange.max", 5 ] },
                   { "$lt": [ "$$m.twaRange.min", 32 ] },
                   { "$gt": [ "$$m.twaRange.max", 32 ] }
                 ]
               }
             }
           }
         }
       }
     }
  }}
]

And produces the matched document output as:

{
    "_id" : ObjectId("593bc2f15924d4206cc6e399"),
    "name" : "race",
    "polaire" : [
        {
            "voile" : "foc",
            "matrice" : [
                    {
                            "vitRange" : {
                                    "min" : 4,
                                    "max" : 6
                            },
                            "twaRange" : {
                                    "min" : 30,
                                    "max" : 33
                            },
                            "values" : [
                                    0,
                                    0,
                                    2.4,
                                    3.7
                            ]
                    }
            ]
        }
    ]
}

The "query" portion of $match is important to actually select the "document(s)" that meet the conditions. Without the usage of $elemMatch the expression can actually match documents without the correct conditions on the same inner elements and in fact would be spread across all array elements present in the document(s).

Filtering the array which is nested first uses $map since the "inner" array element is also going to be subject to its own "filtering". So both the "input" source for the $map as well as the "output" as "in" make reference to $filter conditions in order to match the specific element(s) of the arrays.

As the "conditions" ( "cond" ) to $filter we make use of "logical aggregation expressions" such as the boolean $and as well as the other "comparison operators" to mimic the same conditions of their "query operator" counterparts. These are responsible for the logic that matches the correct array items to return in the "filtered" result.

---

For reference this is the source data from which the results are obtained which should be the same as posted in the question:

{
        "_id" : ObjectId("593bc2f15924d4206cc6e399"),
        "name" : "race",
        "polaire" : [
                {
                        "voile" : "foc",
                        "matrice" : [
                                {
                                        "vitRange" : {
                                                "min" : 0,
                                                "max" : 4
                                        },
                                        "twaRange" : {
                                                "min" : 0,
                                                "max" : 30
                                        },
                                        "values" : [
                                                0,
                                                0,
                                                0,
                                                2.4
                                        ]
                                },
                                {
                                        "vitRange" : {
                                                "min" : 4,
                                                "max" : 6
                                        },
                                        "twaRange" : {
                                                "min" : 30,
                                                "max" : 33
                                        },
                                        "values" : [
                                                0,
                                                0,
                                                2.4,
                                                3.7
                                        ]
                                }
                        ]
                },
                {
                        "voile" : "spi",
                        "matrice" : [
                                {
                                        "vitRange" : {
                                                "min" : 0,
                                                "max" : 4
                                        },
                                        "twaRange" : {
                                                "min" : 0,
                                                "max" : 30
                                        },
                                        "values" : [
                                                0,
                                                0,
                                                0,
                                                1.4
                                        ]
                                },
                                {
                                        "vitRange" : {
                                                "min" : 4,
                                                "max" : 6
                                        },
                                        "twaRange" : {
                                                "min" : 30,
                                                "max" : 33
                                        },
                                        "values" : [
                                                0,
                                                0,
                                                1.4,
                                                2.2
                                        ]
                                }
                        ]
                }
        ]
}