如何使用 Hibernate 和 JPA 处理填充下拉列表？
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【中文标题】如何使用 Hibernate 和 JPA 处理填充下拉列表？【英文标题】：How to handle populating dropdown with Hibernate and JPA? 【发布时间】：2021-06-07 10:18:56 【问题描述】：大家好，我正在通过一个简单的项目学习 Hibernate 和 JPA，该项目允许用户编辑 mysql 数据库中的学生信息字段。有两张桌子 - 一张给学生，一张给他/她的Favorite Movie。 学生只能从下拉列表中选择一部电影，但是我想不出如何用 中的数据（电影名称）填充下拉列表>最喜欢的电影表
Student.java
@Entity
@Table(name = "student")
@NamedQueries(
@NamedQuery(name = "Student.findAll", query = "SELECT s FROM Student s"))
public class Student implements Serializable
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id_student")
private Integer idStudent;
@Column(name = "name")
private String name;
@JoinColumn(name = "id_movie", referencedColumnName = "id_movie")
@ManyToOne(cascade = CascadeType.ALL)
private FavoriteMovie favoriteMovie;
/* Getters/Setters */
@Override
public int hashCode()
int hash = 0;
hash += (idStudent != null ? idStudent.hashCode() : 0);
return hash;
@Override
public boolean equals(Object object)
if (!(object instanceof Student))
return false;
Student other = (Student) object;
if ((this.idStudent == null && other.idStudent != null) || (this.idStudent != null && !this.idStudent.equals(other.idStudent)))
return false;
return true;
@Override
public String toString()
return "Student" + "idStudent=" + idStudent +
", name=" + name +
", favoriteMovie=" + favoriteMovie + '';
FavoriteMovie.java
@Entity
@Table(name = "favorite_movie")
@NamedQueries(
@NamedQuery(name = "FavoriteMovie.findAll", query = "SELECT m FROM FavoriteMovie m"))
public class FavoriteMovie implements Serializable
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id_movie")
private Integer idFavoriteMovie;
@Column(name = "movie_name")
private String favoriteMovieName;
@Column(name = "movie_year")
private int favoriteMovieYear;
@OneToMany(mappedBy = "favoriteMovie")
private List<Student> studentList;
public FavoriteMovie()
public FavoriteMovie(Integer idFavoriteMovie)
this.idFavoriteMovie = idFavoriteMovie;
public FavoriteMovie(Integer idFavoriteMovie, String favoriteMovieName)
this.idFavoriteMovie = idFavoriteMovie;
this.favoriteMovieName = favoriteMovieName;
/* Getters/Setters */
EditServlet.java
@WebServlet("/EditServlet")
public class EditServlet extends HttpServlet
private static final long serialVersionUID = 1L;
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
String idStudent = request.getParameter("idStudent");
StudentService studentService = new StudentService();
Student student = studentService.findStudent(Integer.parseInt(idStudent));
HttpSession session = request.getSession();
session.setAttribute("student", student);
request.getRequestDispatcher("/WEB-INF/editStudent.jsp").forward(request, response);
@Override
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
String action = request.getParameter("modify");
if ("modify".equals(action))
String name = request.getParameter("name");
HttpSession session = request.getSession();
Student student = (Student) session.getAttribute("student");
student.setName(name);
String favoriteMovieName = request.getParameter("favoriteMovieName");
student.getFavoriteMovie().setFavoriteMovieName(favoriteMovieName);
StudentService studentService = new StudentService();
studentService.saveStudent(student);
session.removeAttribute("student");
request.getRequestDispatcher("/index.jsp").forward(request, response);
editStudent.jsp
<body>
Modify Student
<br/>
<form name ="form1" action="$pageContext.request.contextPath/EditServlet" method="post">
Id Student: <input type="text" name="idStudent" value="$student.idStudent" readonly="readonly"><br/>
Name: <input type="text" name="name" value="$student.name"><br/>
Favorite Movie: <select name="selectedFavoriteMovie" id="selectedFavoriteMovie">
<c:forEach var="favoriteMovie" items="" >
<option value="">
</option>
</c:forEach>
</select><br/><br/>
<input type="submit" name="edit" value="edit">
</form>
</body>
必须使用 FavoriteMovies 表中的所有 电影名称 填充下拉列表。
【问题讨论】：
【参考方案1】：我认为它非常适合您当前的解决方案，无需进行太多修改 :) 我想 - 因为你有一个 StudentService - 你也有一个可以做的 FavoriteMovieService：
List<FavoriteMovie> movies = new FavoriteMovieService().getAll();
如果是这样 - 您可以在 GET 请求上为 servlet 添加一个附加属性，如下所示：
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
String idStudent = request.getParameter("idStudent");
StudentService studentService = new StudentService();
Student student = studentService.findStudent(Integer.parseInt(idStudent));
List<FavoriteMovie> movies = new FavoriteMovieService().getAll();
HttpSession session = request.getSession();
session.setAttribute("student", student);
session.setAttribute("movies", movies);
request.getRequestDispatcher("/WEB-INF/editStudent.jsp").forward(request, response);
之后，您将能够在 JSP 中遍历该列表：
<c:forEach items="$movies" var="movie">
<option value="$movie.getFavoriteMovieName()">$movie.getFavoriteMovieName()</option>
</c:forEach>
这应该对你有用:)
UPD：
-
如何在下拉列表中显示所选电影：
<c:forEach items="$movies" var="movie">
<option value="$movie" selected="$movie.getFavoriteMovieName() == student.getFavouriteMovie().getFavouriteMovieName()">$movie.getFavoriteMovieName()</option>
</c:forEach>
-
如何更新电影：
@Override
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
String action = request.getParameter("modify");
if ("modify".equals(action))
String name = request.getParameter("name");
HttpSession session = request.getSession();
Student student = (Student) session.getAttribute("student");
student.setName(name);
FavoriteMovie favoriteMovie = request.getParameter("favoriteMovieName");
student.setFavoriteMovie(favoriteMovie);
StudentService studentService = new StudentService();
studentService.saveStudent(student);
session.removeAttribute("student");
request.getRequestDispatcher("/index.jsp").forward(request, response);
【讨论】：
嘿，这非常适合列出所有可用的电影。但是有两个问题我无法解决。尝试更改学生最喜欢的电影时，表单不会提交新的最喜欢的电影。当学生有喜欢的电影时，它不会在下拉列表中选择。你能再推我一次吗:) 当然！我会尽快为您更新问题） 当试图更改电影标题时，它会更改 FavoriteMovie 表中的值，这是不受欢迎的行为，因为我只是学生在电影之间切换而不修改最喜欢的电影表。 嗨！请坚持：<c:forEach items="$movies" var="movie"> <option value="$movie" selected="$movie.getFavoriteMovieName() == student.getFavouriteMovie().getFavouriteMovieName()">$movie.getFavoriteMovieName()</option> </c:forEach> 在哪里使用传递整个 FavoriteMovie 类作为值，而不仅仅是电影名称。并将其保存如下：FavoriteMovie favoriteMovie = request.getParameter("favoriteMovieName"); student.setFavoriteMovie(favoriteMovie);这将更新对学生记录的FavoriteMovie的引用，并且不会重写电影`【参考方案2】：
你有
<select name="selectedFavoriteMovie" id="selectedFavoriteMovie">
所以你也应该这样做：
request.getParameter("selectedFavoriteMovie");
也代替
<option value="$movie.getFavoriteMovieName()">$movie.getFavoriteMovieName()</option>
你可以这样做：
<option value="$movie">$movie.getFavoriteMovieName()</option>
在这种情况下，变量 selectedFavoriteMovie 将输入 FavoriteMovie 而不是 String，您将能够执行 student.setFavoriteMovie(selectedFavoriteMovie);
要选择实际选择的FavoriteMovie，您需要将selected 添加到option 。它可以通过几种方式完成，例如
<option value="$movie" $movie.getId() == student.getFavoriteMovie().getId() ? "selected" : "">$movie.getFavoriteMovieName()</option>
【讨论】：
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