MongoDB - FindById is not working and giving null - mongodb

Question

I am using Spring Boot(V2.2.2.RELEASE) + Spring Data Mongo Example. In this example, I've records like below
{
"_id" : ObjectId("5cb825e566135255e0bf38a4"),
"firstName" : "John",
"lastName": "Doe"
}
My Repository
#Repository
public interface EmployeeRepository extends CrudRepository<Employee, ObjectId>{
Employee findById(String id);
}
Code
Employee findById = employeeRepository.findById("5cb825e566135255e0bf38a4");
System.out.println(findById);
Even below code not working
Query query = new Query(Criteria.where("id").is(new ObjectId("5cb825e566135255e0bf38a4")));
List<Employee> find = mongoTemplate.find(query, Employee.class);

Answer 1

Seems there might be two issues
ObjectId should be used
employeeRepository.findById(new ObjectId("5cb825e566135255e0bf38a4"))
ID field goes with underscore
new Query(Criteria.where("_id").is(new ObjectId("5cb825e566135255e0bf38a4")))
I'm not a Java guy, so might miss smth, but at least give it a try :)

Answer 2

Using the input document with _id: ObjectId("5cb825e566135255e0bf38a4") you can use either of the approaches. Assuming there is the document in the employee collection you can query by the _id's string value.
public class Employee {
#Id
private String id;
private String name;
// constructors (with and with arguments)
// get methods
// override toString()
}
// Spring-data app using MongoTemplate
MongoOperations mongoOps = new MongoTemplate(MongoClients.create(), "test");
Query query = new Query(where("id").is("5cb825e566135255e0bf38a4"));
Employee emp = mongoOps.findOne(query, Employee.class);
-or-
MongoRepository
interface extends CrudRepository and exposes the capabilities of the
underlying persistence technology in addition to the generic
persistence technology-agnostic interfaces such as CrudRepository.
#Repository
public interface EmployeeRepository extends MongoRepository<Employee, String> {
#Query("{ 'id' : ?0 }")
Optional<Employee> findById(String id);
}
// Spring-data app using the Repository
Optional<Employee> empOpt = employeeRepository.findById("5cb825e566135255e0bf38a4");
if (empOpt.isPresent()) {
System.out.println(empOpt.get());
}
else {
System.out.println("Employee not found!");
}

Answer 3

I too faced the issue. Interestingly things are working fine with version 2.1.7RELEASE
<documentRepository>.findById(<StringID>) treats as String Id in 2.2.2RELEASE
while 2.1.7RELEASE transforms it to ObjectId and hence the find query works.