通过Thymeleaf模板传递SPRING应用程序中更改的子对象的问题

Question

我正在开发测试任务-报价书（未经授权）。我有两个实体：报价和作者。这里有代码：

@Entity
@Table(name="authors")
public class Author {
    @Id
    @SequenceGenerator(name="author_id_seq", sequenceName="author_id_seq", allocationSize=1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "author_id_seq")
    @Column(name = "id")
    private long id;

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

    public Author() {
    }

    public Author(long id, String nickName) {
        this.id = id;
        nickName = nickName;
    }
/*
Getters and Setters
*/
}

报价：

@Entity
@Table(name = "quotes")
public class Quote {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "quotes_id_seq")
    @SequenceGenerator(name="quotes_id_seq", sequenceName="quotes_id_seq", allocationSize=1)
    @Column(name = "id")
    private long id;
    @Column(name = "content")
    private String content;
   // @Temporal(TemporalType.DATE)
    @Column(name = "date")
    private LocalDate date;
    @ManyToOne
    @JoinColumn(name = "author")
    private Author author;

    public Quote() {
    }

    public Quote(long id, String content, LocalDate date, Author author) {
        this.id = id;
        this.content = content;
        this.date = date;
        this.author = author;
    }
/*
Getters and Setters
*/
}

我的Thymeleaf模板包含带有两个输入字段（for Quote.Content和for Quote.Author.Nickname）的form，以及带有现有作者的select。我想看到这样的行为，当我为author、content填充输入时，如果authors表中不存在author，我的应用程序在这个表中添加来自输入昵称和生成ID的指定值的行。但问题是从Thymeleaf模板中得到我意想不到的结果。Template将带author的Quote对象传递给Controll，该对象的昵称为null而不是来自我输入的值。有我的表单的thymeleaf模板代码：

 <form action="#" th:action="@{/newQuote}" th:object="${quote}" method="post">
                <div class="form-row">
                    <div class="form-group col-md-3">
                        <label class="sr-only" for="inputNick">Nick Name</label>
                        <!--/*@thymesVar id="author" type="hello.entity.Author"*/-->
                        <input type="text" class="form-control" id="inputNick" th:field="*{author.nickName}"
                               placeholder="enter Nick Name">
                    </div>
                    <div class="form-group col-md-6">
                        <select id="nickNames">
                            <th:block th:each="author : ${allAuthors}">
                                <option th:text="${author.nickName}">Nick Name</option>
                            </th:block>
                        </select>
                    </div>
                    <div class="form-group col-md-12">
                        <label for="postContent">Your Quote:</label>
                        <input type="text" class="form-control" id="postContent" th:field="*{content}"
                               placeholder="quote text">
                    </div>
                </div>

                    <div class="form-group col-md-2">
                        <input type="submit" value="Add Quote"/>
                    </div>
                    <div class="form-group col-md-2">
                        <input type="reset" value="Reset"/>
                    </div>

            </form>

@GetMapping("/newQuote")
    public String showAuthors(Model model){
        model.addAttribute("allAuthors",authorService.findAll());
        model.addAttribute("quote", new Quote());
        return "newQuote";
    }

    @PostMapping("/newQuote")
    public String addQuote (@ModelAttribute Quote quote) {
        quote.setDate(LocalDate.now());
        quoteRepository.save(quote);
        return "redirect:/";

null

我知道我可以用字段昵称insteadof author字段创建DTO类并在Controller的postmapping方法中将其转换为我的实体类。但我认为这是“不好的练习”的方式。我想，当我试图更改author对象并将其从thymeleaf传递到Controller时，我可能做了错误的步骤。而且我也认为，在这种情况下，没有办法实现这个逻辑。我不知道真相在哪里。请帮我找到它。

附言：对不起，我的英语不好

Answer 1

答案是如何同时添加一个引号和它的作者。因为我们的作者不存在，所以选择方法是不可能的。实现这一点的简单方法是更改quote实体并将@Cascade(CascadeType.Persist)添加到quote中的author字段。这将自动坚持作者与您的报价。

这些将是完成此任务所需的对代码的更改。

更新

@PostMapping("/newQuote")
public String addQuote (@ModelAttribute Quote quote,
                        @RequestParam("nickName") String nickName) {
    // This will automatically persist your quote and it's author.
    quote.setDate(LocalDate.now());
    Author author = new Author();
    author.setNickName(nickName);
    quoteRepository.save(quote);
}

报价实体

@Entity
@Table(name = "quotes")
public class Quote {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "quotes_id_seq")
    @SequenceGenerator(name="quotes_id_seq", sequenceName="quotes_id_seq", allocationSize=1)
    @Column(name = "id")
    private long id;

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

    @Column(name = "date")
    private LocalDate date;

    @ManyToOne
    @Cascade(CascadeType.PERSIST)
    @JoinColumn(name = "author")
    private Author author;

    // Getters and Setters
}

重要的是，确保注意到我们正在向作者字段添加一个新的注释@cascade(CascadeType.persist)。

HTML

<form action="#" th:action="@{/newQuote}" th:object="${quote}" method="post">
    <div class="form-row">
        <div class="form-group col-md-3">
            <label class="sr-only" for="inputNick">Nick Name</label>
            <!--/*@thymesVar id="author" type="hello.entity.Author"*/-->
            <input type="text" name="nickName" class="form-control" id="inputNick" placeholder="enter Nick Name"/>
        </div>
        <div class="form-group col-md-12">
            <label for="postContent">Your Quote:</label>
            <input type="text" class="form-control" id="postContent" th:field="*{content}" placeholder="quote text"/>
        </div>
   </div>
   <div class="form-group col-md-2">
       <input type="submit" value="Add Quote"/>
   </div>
   <div class="form-group col-md-2">
      <input type="reset" value="Reset"/>
   </div>
</form>