无法在讲师班上设置讲师 car_id答案

【问题标题】：Cannot set instructor car_id on Instructor class无法在讲师班上设置讲师 car_id
【发布时间】：2020-01-22 19:05:18
【问题描述】：

我有几个实体，我可以用他的 id、姓名、姓氏、城市、地址保存 Instructor，但我可以用百里香形式在 car_id 上设置他的引用。在引导加载程序上很好

模板解析时出错（模板：“类路径资源[templates/index.html]”） org.thymeleaf.exceptions.TemplateInputException：模板解析时出错（模板：“类路径资源[templates/index.html]”）引起：org.attoparser.ParseException：评估 SpringEL 表达式的异常：“car.getInstructor().id”（模板：“index” - 第 84 行，第 13 列）

在讲师课上我做了这个
@OneToOne(cascade = CascadeType.ALL,fetch = FetchType.LAZY) 私家车；在汽车课上我做了这个 @OneToOne 私人讲师讲师；

<body>
    <form th:object="${instructor}" th:action="@{/instructor/}" method="post">
        <input type="hidden" th:field="*{id}"/>
        First name<br>
        <input type="text" class="form-control" th:field="*{firstName}"/><br>
        Last name <br>
        <input type="text" class="form-control" th:field="*{lastName}"/><br>
        City <br>
        <input type="text" class="form-control" th:field="*{city}"/><br>
        Address <br>
        <input type="text" class="form-control" th:field="*{address}"/><br>

      <input type="number" class="form-control" th:field="*{car.id}"/><br>
        <button type="submit">Submit</button>
    </form>
</body>

@Slf4j @控制器公共类 IndexController {

    private final InstructorService instructorService;
    private final StudentService studentService;
    private final CarService carService;
    private final CarDrivingClassService carDrivingClassService;

    public IndexController(InstructorService instructorService, StudentService studentService, CarService carService, CarDrivingClassService carDrivingClassService) {
        this.instructorService = instructorService;
        this.studentService = studentService;
        this.carService = carService;
        this.carDrivingClassService = carDrivingClassService;
    }


    @RequestMapping({"", "/", "/index"})
    public String getIndexPage(Model model) {

        System.out.println("Getting Index page");
        model.addAttribute("cars",carService.findAll());
        model.addAttribute("instructors", instructorService.findAll());
        model.addAttribute("students", studentService.findAll());

        return "index";
    }

    @GetMapping("/new")
    public String newRecipe(Model model){
        model.addAttribute("instructor", new InstructorCommand());

        return "/form";
}
    @PostMapping("instructor")
    @Transactional
    public String saveOrUpdate(@ModelAttribute InstructorCommand command){

        InstructorCommand savedCommand = instructorService.saveInstructorCommand(command);

        return "redirect:/";
    }


}

@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table(name="cars")
public class Car extends BaseEntity{

    @Column(name = "name")
    private String name;

    @OneToOne
    private Instructor instructor;


}

@Setter
@Getter
@NoArgsConstructor
@AllArgsConstructor
@Builder
@Entity
@Table(name="instructors")
public class Instructor extends Person{

    @OneToMany(mappedBy = "instructor")
    public  Set<Student> students = new HashSet<>();

    @OneToOne(cascade = CascadeType.ALL,fetch = FetchType.LAZY)
    private Car car;


}

【问题讨论】：

在这个car.id 的形式中可能是id 而不是car.id
我试了还是不行，

标签： java spring hibernate annotations

【解决方案1】：

我正在用这个加载数据

@Component
public class Bootstrap implements CommandLineRunner {

    private final CarService carService;
    private final StudentService studentService;
    private final InstructorService instructorService;
    private final CarDrivingClassService carDrivingClassService;

    public Bootstrap(CarService carService, StudentService studentService, InstructorService instructorService, CarDrivingClassService carDrivingClassService) {
        this.carService = carService;
        this.studentService = studentService;
        this.instructorService = instructorService;
        this.carDrivingClassService = carDrivingClassService;
    }

    @Override
    public void run(String... args) throws Exception {

        Date date = new SimpleDateFormat( "yyyyMMdd" ).parse( "19970807" );
        Date date2 = new SimpleDateFormat( "yyyyMMdd" ).parse( "20192304" );
        Date date3 = new SimpleDateFormat( "yyyyMMdd" ).parse( "20192404" );
        Date date4 = new SimpleDateFormat( "yyyyMMdd" ).parse( "20192505" );

        /*Creating a student*/
        Student student = new Student();
        student.setFirstName("Bob");
        student.setLastName("Rock");
        student.setBirthDate(date);
        student.setCity("Miami");
        student.setAddress("Lincoln Road");
        student.setPostalCode(45300);

        Student student2 = new Student();
        student2.setFirstName("John");
        student2.setLastName("Smith");
        student2.setBirthDate(date);
        student2.setCity("Miami");
        student2.setAddress("Old Cutler Road and Ingraham Highway");
        student2.setPostalCode(45100);

        /*Class that will save our classes for driving*/
        CarDrivingClass savedDrivingClasses;

        //Create 20 car driving classes and save them in table CLASSES
        for(int i = 0; i<20; i++){
            CarDrivingClass tempClass = new CarDrivingClass();
            tempClass.setDate(date3);
            savedDrivingClasses = carDrivingClassService.save(tempClass);
            /*
            Fill table STUDENT_CLASSES
            * */
            student.getClasses().add(savedDrivingClasses);
            student2.getClasses().add(savedDrivingClasses);
            System.out.println("Saving "+(i+1)+ ". class");
        }
        /*Instructor one*/
        Instructor instructor = new Instructor();
        instructor.setFirstName("Dave");
        instructor.setLastName("Joe");
        instructor.setCity("Miami");
        instructor.setAddress("Miami 001");
        instructor.setPostalCode(45400);

        /*Instructor two*/
        Instructor instructor2 = new Instructor();
        instructor2.setFirstName("Clark");
        instructor2.setLastName("Kent");
        instructor2.setCity("LA");
        instructor2.setAddress("South Martel Avenue");
        instructor2.setPostalCode(95400);

        /*Car num one*/
        Car audi = new Car();
        audi.setName("Audi A7");
        audi.setInstructor(instructor);

        /*Car num two*/
        Car BMW = new Car();
        BMW.setName("BMW M4");
        BMW.setInstructor(instructor2);

        /*Adding car to instructors*/
        instructor.setCar(audi);
        instructor2.setCar(BMW);

        /*Associate student with instructor*/
        student.setInstructor(instructor);
        student2.setInstructor(instructor);

        //Saving into db with services
        instructorService.save(instructor);
        instructorService.save(instructor2);
        studentService.save(student);
        studentService.save(student2);
        carService.save(audi);
        carService.save(BMW);

    }
}

数据显示正常

<h1>Instructors</h1>
<table>
    <thead>
    <tr>
        <th>ID</th>
        <th>Name</th>
        <th>Surname</th>
        <th>City</th>
        <th>Address</th>
        <th>Car</th>
    </tr>
    </thead>
    <tr th:remove="all">
        <td>123</td>
        <td>Tasty Goodnees 1</td>
        <td><a href="#">View</a></td>
    </tr>
    <tr th:each="instructor : ${instructors}">
        <td th:text="${instructor.id}">334</td>
        <td th:text="${instructor.firstName}">Tasty Goodnees 3</td>
        <td th:text="${instructor.lastName}">Tasty Goodnees 3</td>
        <td th:text="${instructor.city}">Tasty Goodnees 3</td>
        <td th:text="${instructor.address}">Tasty Goodnees 3</td>
        <td th:text="${instructor.getCar().id}">Tasty Goodnees 3</td> <!--getting car id -->
    </tr>
</table>

但是当我添加一个新的 Instructor 时，它会以索引形式向我显示这个 ${instructor.getCar().id 的错误，我可以在没有输入字段的情况下在表单中添加教练，并在 index.html 中添加这行代码美味佳肴 3

【讨论】：