Composite Primary Key using MongoDB and Spring Data JPA

Question

Could someone tell how to create a composite key in Spring Data JPA using Mongo DB

Answer 1

You cannot use MongoDB with Spring Data JPA because JPA is for relational databases like MySQL.

Instead you have to use Spring Data MongDB and you will find the documentation here:

https://docs.spring.io/spring-data/mongodb/docs/2.1.8.RELEASE/reference/html/

But here's an example with a composite key:

class StudentChairman {

    @Id
    private CompositeKey id;

    // getters and setters

    static class CompositeKey implements Serializable {
        private String studentId;
        private String groupId;

        // getters and setters
    }
}

Answer 2

The composite/compound primary key feature in MongoDB can be achieved using the below approach

For instance, we are creating an Employee document where the employee_id and department Should be unique

Entity class

@Document(collection = "employee")
@CompoundIndex(name = "employee_unique_idx", def = "{'employeeId': 1, 'department': 1}", 
unique = true)
public class Employee {
    @Id
    private String id;
    private String employeeId;
    private String department;
    private String organization;
}

DB creation part, you can create the unique composite key manually by

db.employee.createIndex( { "employeeId": 1, "department": 1 }, { unique: true } )

or using the java client

try (MongoClient mongoClient = MongoClients.create(uri)) {
    String databaseName = "demo-db";
    MongoDatabase database = mongoClient.getDatabase(databaseName);
    MongoCollection<Document> employee = database.getCollection("employee");
    IndexOptions indexOptions = new IndexOptions();
    //Enforcing unique key const
    indexOptions.unique(true);
    //creating unique composite key
    employee.createIndex(compoundIndex(ascending("employeeId"), descending("department")), 
    indexOptions);

}

Asserting the unique key condition

    @Autowired
    private EmployeeRepository employeeRepository;

    @Test
    void crudEmployee() {
        Employee employee1 = new Employee();
        employee1.setEmployeeId("emp1");
        employee1.setDepartment("Data Engineer");
        employee1.setOrganization("Freelancer");

        Employee employee2 = new Employee();
        employee2.setEmployeeId("emp2");
        employee2.setDepartment("Data Engineer");
        employee2.setOrganization("Freelancer");

        Employee employee3 = new Employee();
        employee3.setEmployeeId("emp1");
        employee3.setDepartment("Data Engineer");
        employee3.setOrganization("Freelancer");

        employeeRepository.save(employee1);
        employeeRepository.save(employee2);
        //we are trying to create duplicate entry but the mongo
        //will not allow it because of unique key constraint
        Assertions.assertThrows(org.springframework.dao.DuplicateKeyException.class,
                () -> employeeRepository.save(employee3));
    }