How to filter array in Mongodb document using Spring

Question

I have below document structure.

{
    "_id" : { "teacherId" : "<teacherId>", "Year" : "<Year>" },
    "groups" : [ {
        "groupId" : "<uuid>",
        "groupName" : "<name>",
        "groupNameLowerCase" : "<name_in_lower_case>",
        "description" : "<desc>",
        "students" : ["<studentid1>", "<studentid2>", ...],
        "editedDate" : "<currentTimestamp>"
        },
        ...
    ],
    "editedDate" : "<currentTimestamp>",
    "points" : "<points>"
}

Consider that below two documents are present in DB

{
    "_id" : { "teacherId" : "1", "Year" : "2016" },
    "groups" : [ {
        "groupId" : "123",
        "groupName" : "Test1",
        "groupNameLowerCase" : "test1",
        "description" : "sample document",
        "students" : ["11", "22"]
         },
    {
        "groupId" : "234",
        "groupName" : "Test2",
        "groupNameLowerCase" : "test2",
        "description" : "sample document",
        "students" : ["11", "22"]
         },
        {
        "groupId" : "345",
        "groupName" : "Test3",
        "groupNameLowerCase" : "test3",
        "description" : "sample document",
        "students" : ["21", "32"]
         }
    ],
    "points" : "650"
}

{
    "_id" : { "teacherId" : "1", "Year" : "2015" },
    "groups" : [ {
        "groupId" : "123",
        "groupName" : "HOCKEY",
        "groupNameLowerCase" : "HOCKEY",
        "description" : "HOCKEY team",
        "students" : ["11", "22"]
         },
        {
        "groupId" : "234",
        "groupName" : "football",
        "groupNameLowerCase" : "football",
        "description" : "sample football",
        "students" : ["11", "22"]
         },
        {
        "groupId" : "345",
        "groupName" : "Test3",
        "groupNameLowerCase" : "test3",
        "description" : "sample document",
        "students" : ["21", "32"]
         }
    ],
    "points" : "650"

I want to select groups for the specified student and teacher combination. e.g. If I supply teacherid= 1 and student id =11 then query should return two documents with matching groups. I wrote below code to get the matching groups in document. But afterward I understand that elemMatch will only return first element matching. It will return two documents but with only one group in it.

Here I would like to understand the options available in Mongodb 2.4 to filter arrays in document returned by some query.

String teacherId = "1";
String studentId = "11";

Criteria documentSearchCriteria = where("_id.teacherId").is(teacherId)
                .and("groups")
                .elemMatch(where("students").in(studentId));

Criteria groupFilterCriteria = where("groups").elemMatch(where("students").in(studentBid));
BasicQuery query = new BasicQuery(documentSearchCriteria.getCriteriaObject(), groupFilterCriteria.getCriteriaObject());
List<GroupsDocument> groupsDocumentList = groupsMongoTemplate.find(query, GroupsDocument.class);

venkat.s · Accepted Answer · 2016-11-16 07:33:28Z

1

As you said elemMatch will retrieve only first object in an array so you have to use aggregate future to achieve your output

    MatchOperation match = Aggregation.match(Criteria.where("_id.teacherId").is("1").and("groups.students").in(11));
    UnwindOperation unwind = Aggregation.unwind("groups");
    GroupOperation group = Aggregation.group("_id").push("groups").as("groups").first("points").as("points");
    Aggregation aggregation = Aggregation.newAggregation(unwind, match, group);
    AggregationResults<BasicDBObject> groupResults = mongoTemplate.aggregate(aggregation,
                    CustomGroupsDocument.class, BasicDBObject.class);
    List<BasicDBObject> result = groupResults.getMappedResults();

edited Nov 16, 2016 at 7:33

answered Nov 16, 2016 at 7:17

venkat.s

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1 Comment

Sachin Over a year ago

Do you have any example for it

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