Spring and MongoDB manual references

[Aca Vidak]

Hi everyone,

I need advice on doing manual references in mongodb with spring without using dbrefs.

If for example, I have two document collections:

User {
...
addresses: [addressId1, addressId2...]
}

Address {
..
}

So, user has 1 or more addresses. In user document, I want to use array of address ids.

Now, there is a question of inserting, updating and retrieving user document.

For insertion, I would need one POJO which has addresses as array of ids (array of ObjectIds, Strings..).

For retrieving, sometimes I need full document with addresses eagerly populated. For this case I would need different POJO which has addresses as array of address objects.

Is there any good approach to this? Any pieces of advice?

[Prasad Saya]

The User and Address data is a one-to-many relationship. A user can have, in general, 1 to 3 ( a small number) addresses. In MongoDB, this is modeled by embedding the address data into the user data.

It is unusual, to create two collections one for each of the user and the address - especially when the addresses are going to be a very small number, and the kind of data being stored. The document structure would be something like this in a "user" collection:

{        "_id" : ObjectId("5e55e7eb7903141b80592746"),        "name" : "John",        "address" : [                {                        "street" : "111 10th St.",                        "city" : "New York"                },                {                        "street" : "222 24th Rd.",                        "city" : "New York"                }        ] }

Note the address is an array type field, with multiple address elements.

The two Java POJOs are the User and the Address. The User class will have a property called as address of type List<Address>. Using Spring-Data APIs for MongoDB, the CRUD operations can be performed on the "user" collection. For example, using MongoTemplate class:

private static void addUser() {
    MongoOperations mongoOps = new MongoTemplate(MongoClients.create(), "testDB");
    Address addr1 = new Address("111 10th St.", "New York");
    Address addr2 = new Address("222 24th Rd.", "New York");
    User user1 = new User("John", Arrays.asList(addr1, addr2));
    mongoOps.insert(user1, "user"); // "user" refers to the collection name
}

private static void getUsers() {
    MongoOperations mongoOps = new MongoTemplate(MongoClients.create(), "testDB");
    Query qry = new Query(Criteria.where("name").is("John"));
    List<User> users = mongoOps.find(qry, User.class);
    users.forEach(System.out::println); // prints the document as shown above
}

References:

Data Model Design

MongoTemplate

NOTE: One can also consider using MongoDB Java Driver APIs for the same application.