为什么Spring BootmongoDb findAll（）返回空数组？

Question

我有一个Spring Boot应用程序连接到本地mongoDB数据库。当我试图从集合中获取所有记录时，它返回一个空数组。在输出中，它表示已连接到端口27017。它在运行应用程序时不会给我任何错误，但在我键入时只返回一个空数组http://localhost:8080/courses/我错过了什么？

模范班

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;
    }

}

控制器类

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);
    }
}

存储库类

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输出

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

出现这个问题的原因是，模型类中没有明确给出集合名称，因此spring data将集合名称从类名（Courses）派生为驼峰大小写（Courses）。由于您的实际收藏名为课程，因此未找到任何结果。

你必须要么：

>

将集合重命名为课程。或

像这样用正确的集合名称注释模型类：

@Document（collection=“Courses”）

公共类课程{