Why does Spring-boot with mongoDb findAll() return empty array?

Question

I have a spring boot application connecting to a local mongoDB database. When I try to fetch all records from a collection it returns an empty array.In the output it says connected to port 27017. It does not give me any error while running the application but just returns an empty array when I type http://localhost:8080/courses/ What am I missing here?

Model class

package SpringBoot.Training.Management.Tool.SpringBootTMTCourses.Model;

import org.bson.types.ObjectId;
import org.springframework.data.annotation.Id;

public class Courses {
    @Id
    public ObjectId _id;

    public String courseID;
    public String courseName;

    public Courses(ObjectId _id, String courseID, String courseName) {
        super();
        this._id = _id;
        this.courseID = courseID;
        this.courseName = courseName;
    }

    public String get_id() {
        return _id.toHexString();
    }

    public void set_id(ObjectId _id) {
        this._id = _id;
    }

    public String getCourseID() {
        return courseID;
    }

    public void setCourseID(String courseID) {
        this.courseID = courseID;
    }

    public String getCourseName() {
        return courseName;
    }

    public void setCourseName(String courseName) {
        this.courseName = courseName;
    }

}

Controller class

package SpringBoot.Training.Management.Tool.SpringBootTMTCourses.Controller;

import java.util.List;

import org.bson.types.ObjectId;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import SpringBoot.Training.Management.Tool.SpringBootTMTCourses.Model.Courses;
import SpringBoot.Training.Management.Tool.SpringBootTMTCourses.Repository.CoursesRepository;

@RestController
@RequestMapping("/courses")
public class CourseController {
    @Autowired
    private CoursesRepository repository;

    @RequestMapping(value = "/", method = RequestMethod.GET)
    public List<Courses> getAllCourses() {
      return repository.findAll();
    }

    @RequestMapping(value = "/{id}", method = RequestMethod.GET)
    public Courses getPetById(@PathVariable("id") ObjectId id) {
      return repository.findBy_id(id);
    }
}

Repository class

package SpringBoot.Training.Management.Tool.SpringBootTMTCourses.Repository;

import org.bson.types.ObjectId;
import org.springframework.data.mongodb.repository.MongoRepository;

import SpringBoot.Training.Management.Tool.SpringBootTMTCourses.Model.Courses;

public interface CoursesRepository extends MongoRepository<Courses, String> {
    Courses findBy_id(ObjectId _id);
}

MongoDb output

db.Courses.find().pretty()
{
        "_id" : ObjectId("5d29c3a58212eda90db024c4"),
        "courseID" : "1",
        "courseName" : "C#"
}
{
        "_id" : ObjectId("5d29c3a58212eda90db024c5"),
        "courseID" : "2",
        "courseName" : "Java"
}
{
        "_id" : ObjectId("5d29c3a58212eda90db024c6"),
        "courseID" : "3",
        "courseName" : "JavaScript"
}

Answer 1

The issue arises because the collection name is not explicitly given in your model class, so spring-data derives the collection name from the class name (Courses) into camel case (courses). Since your actual collection is called Courses, no results are found.

You have to either:

1. Rename the collection to courses. OR

2. Annotate the model class with the correct collection name like so:

   @Document(collection = "Courses")

   public class Courses {