Delete

Deleting records involves removing existing documents from the database. MongoRepository provides methods to perform these deletions, such as delete(), deleteById(), deleteAll(), and custom query methods.

delete (Delete a Single Document)

To delete a single document, you can use the delete() method. This method will delete the specified document from the database.

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class StudentService {
    @Autowired
    private StudentRepository repository;

    public void deleteGrade(Grade grade) {
        repository.delete(grade);
    }
}

To delete a grade by studentId:

@Autowired
private StudentRepository repository;

public void deleteGradeByStudentId(double studentId) {
    Grade grade = repository.findByStudentId(studentId);
    if (grade != null) {
        repository.delete(grade);
        System.out.println("Deleted grade: " + grade);
    }
}

deleteById

To delete a document by its id, you can use the deleteById() method. This method will delete the document identified by the given id.

To delete a grade by its id:

@Autowired
private StudentRepository repository;

public void deleteGradeById(String gradeId) {
    repository.deleteById(gradeId);
    System.out.println("Deleted grade with id: " + gradeId);
}

deleteAll (Delete Multiple Documents)

To delete multiple documents at once, use the deleteAll() method provided by the StudentRepository. You can pass a list of Grade objects to this method, and it will delete all the specified grades.

To delete all grades with studentId greater than or equal to 10000:

@Autowired
private StudentRepository repository;

public void deleteGradesForStudentIdGreaterThanEqual(double studentId) {
    repository.deleteAll(repository.findByStudentIdGreaterThanEqual(studentId));
    System.out.println("Deleted all grades with student_id >= " + studentId);
}

deleteAll

To delete all documents in a collection, you can use the deleteAll() method without any arguments. This method will delete all the documents in the specified collection.

To delete the entire contents of the grades collection:

@Autowired
private StudentRepository repository;

public void deleteAllGrades() {
    repository.deleteAll();
    System.out.println("Deleted the entire grades collection.");
}

Depending on your reasoning for deleting the entire contents of a collecion, it might make more sense for you to just drop the collection. In which case, using the dropCollection() method from MongoTemplate is a far more performant choice;

mongoTemplate.dropCollection("collectionName");