尝试在Spring+Thymeleaf中创建复合jpa对象

Question

我尝试创建一个对象，其中包含另一个对象，使用一个窗体，但是从下拉列表中选择的对象在从Thymeleaf窗体返回时会转换为字符串。这些是我的项目中的实体，它们之间具有1:N的关系：

实体用户

//imports
@Entity
@Table(name = "USERS")
public class User {
    @Id
    @GeneratedValue
    @Column( name ="USER_ID")
    private int id;

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

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

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

    @OneToMany(fetch= FetchType.LAZY, mappedBy="user", cascade = CascadeType.ALL)
    private List<Post> posts;

    //setter & getters & toString

}

实体员额

//imports
@Entity
@Table(name="POSTS")
public class Post {
@Id
@GeneratedValue
@Column(name="POST_ID")
private int id;

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



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

@ManyToOne
@JoinColumn(name="USER_ID",referencedColumnName="USER_ID")
private User user;

//getters & setters & toString

要创建新职位,请执行以下操作：

//In Controller

@RequestMapping(value = "/posts/new")
public String newPost(Model model) {
    model.addAttribute("post", new Post());
    model.addAttribute("users", userService.list());
    return "addPost";       
}

<form th:action="@{/savePost}" th:object="${post}" method="post">
            <tr>
                <td><input type="hidden" th:field="${post.id}" /></td>
            </tr>
            <tr>
                <td>Titulo</td>
                <td>Texto</td>
                <td>Usuario</td>
            </tr>
            <tr>
                <td><input type="text" th:field="${post.tittle}"
                    th:value="${post.tittle}" /></td>
                <td><input type="text" th:field="${post.text}"
                    th:value="${post.text}" /></td>

                <td><select th:field="${post.user}">
                        <option th:each="user : ${users}" th:text="${user.username}"
                            th:value="${user.id}"></option>
                </select></td>


            </tr>
            <tr>
                <td colspan="3"><input class="btn btn-primary" type="submit"
                    value="GUARDAR"></td>
            </tr>

        </form> 

@PostMapping("/savePost")
//@RequestMapping(value = "users/save",method = RequestMethod.POST)
public String savePost(@ModelAttribute Post post) {

    postService.add(post);
    return "redirect:/posts";
}

public class UserFormatter implements Formatter<User> {

@Autowired
@Qualifier("userService")
public GeneralService<User> userService;

@Override
public String print(User object, Locale locale) {
    return (object != null ? object.getUsername() : "");
}

@Override
public User parse(String text, Locale locale) throws ParseException {
    final Integer userId = Integer.parseInt(text);
    return userService.get(userId);
}

}

正在注册：

@SpringBootApplication
public class BootmvchibernateApplication implements WebMvcConfigurer{

 @SuppressWarnings("unchecked")
    @Override
    public void addFormatters(FormatterRegistry registry) {
      registry.addFormatter(new UserFormatter());
    }



public static void main(String[] args) {
    SpringApplication.run(BootmvchibernateApplication.class, args);
}

}

但是当尝试这种方法时，会发现下一个错误，这只是uppon访问/post/new指令（模板addPost不起作用）：

模板分析过程中出错（模板：“class path resource[templates/addpost2.html]”）org.thymeleaf.exceptions.templateInputException：模板分析过程中出错（模板：“class path resource[templates/addpost2.html]”）.....原因：org.attoparser.ParseException：执行处理器“org.thymeleaf.spring5.processor.springOptionFieldTagProcessor”（模板：“AddPost2”-第43行，第8栏）时出错.....原因：org.springframework.core.convert.ConversionFailedException：无法将值“%2”从类型[java.lang.String]转换为类型[@[e-mail] com.julian.bootmvchibernate.model.user]；嵌套异常是org.springframework.core.convert.support.conversionutils.InvokeConverter（conversionutils.java:47)处的java.lang.NullPointerException

如果需要更多的信息，告诉我，我贴出来。编辑：如果有人感兴趣，这就是存储库。github.com/julianbautistavelez/jpa_spring_excercise

Answer 1

问题出在您的addpost.html中，只是现在一切正常。

    <table>
        <form th:action="@{/posts/new/mod}" th:object="${post}"
            method="POST">
            <tr>
                <td><input type="hidden" th:field="${post.id}" /></td>
            </tr>
            <tr>
                <td>Titulo</td>
                <td>Texto</td>
                <td>Usuario</td>
            </tr>
            <tr>
                <td><input type="text" th:field="${post.tittle}"
                    th:value="${post.tittle}" /></td>
                <td><input type="text" th:field="${post.text}"
                    th:value="${newPost.text}" /></td>

                <!-- <td><select th:field="${newPost.user}">
                        <option th:each="user : ${users}" th:text="${user.username}"
                            th:value="${user.id}"></option>
                </select></td> -->

                <td><select th:field="*{user}" class="form-control">
                    <option th:each="user: ${users}"
                        th:value="${user.id}" th:text="${user.username}"></option>
                </select></td>


            </tr>
            <tr>
                <td colspan="3"><input class="btn btn-primary" type="submit"
                    value="GUARDAR"></td>
            </tr>

        </form>
    </table>

我将newpost更改为post，因为您在这里添加的是post模型。

@RequestMapping(value = "/posts/new")
public String newPost(Model model) {
    logger.info("-- en NEW Usuario");
    model.addAttribute("post", new Post());
    model.addAttribute("users", userService.list());
    logger.info("-- -- -- LISTA DE USUARIOS -- -- --");
    System.out.println(userService.list());
    return "addPost";       
}