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Spring Data & MongoDB

MongoRepository Interface

  • Interface: Repository
  • Interface: CrudRepository
  • Interface: PagingAndSortingRepository
  • Interface: MongoRepository
  • Interface: MyCustomRepository (Our own abstraction using IoC)

@Query

Example:

@Query("{'aircraft.nbSeats' : {$gte: ?0}}")
List<FlightInformation> findByMinAircraftNbSeats(int i);

Mongo Document References

In mongo, denormalized data in a single document is optimal. We should always try to minimize relationships between documents.

Relating documents:

  • Manual: Saving the '_id' of a document in another document
  • DBRefs: Link documents together by using the '_id' field, collection name and database name
    • Can link documents across collections or different databases
    • To resolve DBRefs, the application must perform additional queries
    • Cascading is not supported

DBRef formats:

  • $ref
  • $id
  • $db

Example:

{
  "_id": ObjectId("37291b08-9591-4db7-912a-c7ed37cc7ed3"),
  "name": "SomeName",
  "cap": 666,
  "engine": {
    "$ref": "engines",
    "$id": ObjectId("73535742-5097-4a14-ac93-c4a623c5d395"),
    "$db": "atm"   // Optional
  }
}

The order of the formats matters!!! DBRefs are not 'smart'.

Implementation:

@Document
public class Aircraft {
    @Id
    private String id;
    private String name;
    private Integer cap;
    @DBRef
    private Engine engine;
}