Return an element of inner object Spring Repository, Mongodb

Question

I'm using SpringRepository to query mongo db. I have a students collection with documents like the following.

{
    "_id" : ObjectId("52f2139ee4b0384b7402c520"),
    "subjects": [
         {
             "subjectId" : "s001",
             "subjectName" : "maths"
         },
         {
             "subjectId" : "s002",
             "subjectName" : "science"
         },             
    ]
}

I'm going to query this collection using Spring Repository for a subject. I can get a student list with a particular subject like this

@Query("{ 'subjects.subjectName' : ?0 }")
List<Student> findBySubjectName(String subjectName);

But if I want subject only, how to return the a Subject object matching the subject name?

score 0 · Answer 1 · edited May 23 '17 at 10:25

0

This should work: (untested code...)

@Query(value="{ 'subjects.subjectName' : ?0 }", fields="{ 'subjects.$' : 1 }")
List<Student> findBySubjectName(String subjectName);

The basic syntax of projections with @Query can be found here, the projection syntax from this question.

Note that you will still obtain a Student object with null mapped to all fields that have not been fetched. If you don't want that, you will have to implement the query yourself (which is not hard) and return the required field of the fetched document in your method.

edited May 23 '17 at 10:25

Community

1
1

answered Feb 05 '14 at 13:28

chk

534
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12

Can't I fetch Subject object directly? – Susitha Ravinda Senarath Feb 05 '14 at 15:02
for all I know not via annotations – chk Feb 06 '14 at 08:18

Return an element of inner object Spring Repository, Mongodb

1 Answers1