为什么使用mongoDb findAll()的Spring返回空数组？

Question

我有一个spring引导应用程序连接到本地mongoDB数据库。当我尝试从集合中获取所有记录时，它返回一个空的array.In，它说输出连接到端口27017。在运行应用程序时，它不会给我任何错误，但是当我输入http://localhost:8080/courses/时，只返回一个空数组，这里我遗漏了什么？

模型类

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

之所以会出现这个问题，是因为您的模型类中没有显式地给出集合名称，所以spring-data将集合名从类名(Courses)派生为camel case (courses)。由于您的实际集合名为Courses，因此找不到结果。

你必须要么：

1. 将集合重命名为courses。或
2. 用正确的集合名称注释模型类，如下所示： @Document(collection = "Courses") public class Courses {

Answer 2

我也遇到过类似的问题，在回购MatchRepository extends MongoRepository<Match, Integer>中我的自定义方法。

我将标识符从Integer更改为String，它对我有效。比如：MatchRepository extends MongoRepository<Match, String>。