人在江湖

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hibernate一对多双向映射通常通过“多”的一端负责维护关系。但是对于list, 因为list保存关于“顺序”的信息,而多的一端没有这样的信息,所以只能由“一”的一端维护关系。

用在线图书馆举个例子。书和评论之间是一对多的关系。

book代码:

   1: package org.emoticon.library.model;
   2:  
   3: import java.util.ArrayList;
   4: import java.util.Date;
   5: import java.util.List;
   6:  
   7: import javax.persistence.CascadeType;
   8: import javax.persistence.Entity;
   9: import javax.persistence.FetchType;
  10: import javax.persistence.GeneratedValue;
  11: import javax.persistence.Id;
  12: import javax.persistence.JoinColumn;
  13: import javax.persistence.OneToMany;
  14:  
  15: @Entity
  16: public class Book {
  17:     
  18: private Integer id;
  19: private String title;
  20: private String author;
  21: private String description;
  22: private String publisher;
  23: private int pageNumber;
  24: private Date publishTime;
  25: private String isbn;
  26: private List<Comment> comments = new ArrayList<Comment>();
  27:  
  28:  
  29: public void addComment(Comment comment){
  30:     comment.setBook(this);
  31:     comments.add(comment);
  32: }
  33:  
  34: @Id
  35: @GeneratedValue
  36: public Integer getId() {
  37:     return id;
  38: }
  39: public void setId(Integer id) {
  40:     this.id = id;
  41: }
  42: public String getTitle() {
  43:     return title;
  44: }
  45: public void setTitle(String title) {
  46:     this.title = title;
  47: }
  48: public String getAuthor() {
  49:     return author;
  50: }
  51: public void setAuthor(String author) {
  52:     this.author = author;
  53: }
  54: public String getDescription() {
  55:     return description;
  56: }
  57: public void setDescription(String description) {
  58:     this.description = description;
  59: }
  60: public String getPublisher() {
  61:     return publisher;
  62: }
  63: public void setPublisher(String publisher) {
  64:     this.publisher = publisher;
  65: }
  66: public int getPageNumber() {
  67:     return pageNumber;
  68: }
  69: public void setPageNumber(int pageNumber) {
  70:     this.pageNumber = pageNumber;
  71: }
  72: public Date getPublishTime() {
  73:     return publishTime;
  74: }
  75: public void setPublishTime(Date publishTime) {
  76:     this.publishTime = publishTime;
  77: }
  78: public String getIsbn() {
  79:     return isbn;
  80: }
  81: public void setIsbn(String isbn) {
  82:     this.isbn = isbn;
  83: }
  84:  
  85: @OneToMany(fetch = FetchType.EAGER,
  86:         cascade = {CascadeType.ALL})
  87: @JoinColumn (name = "book_id",
  88:         nullable = false)
  89: @org.hibernate.annotations.IndexColumn(name = "comment_position",
  90:         nullable = false,
  91:         base = 1)
  92: public List<Comment> getComments() {
  93:     return comments;
  94: }
  95:  
  96: public void setComments(List<Comment> comments) {
  97:     this.comments = comments;
  98: }
  99:  
 100:  
 101: }

comment代码:

   1: package org.emoticon.library.model;
   2:  
   3: import javax.persistence.CascadeType;
   4: import javax.persistence.Entity;
   5: import javax.persistence.GeneratedValue;
   6: import javax.persistence.Id;
   7: import javax.persistence.JoinColumn;
   8: import javax.persistence.ManyToOne;
   9:  
  10: import junit.framework.Assert;
  11:  
  12: @Entity
  13: public class Comment {
  14: private Integer id;
  15: private int rate;
  16: private String title;
  17: private String content;
  18: private Book book;
  19:  
  20: @Id
  21: @GeneratedValue
  22: public Integer getId() {
  23:     return id;
  24: }
  25: public void setId(Integer id) {
  26:     this.id = id;
  27: }
  28: public int getRate() {
  29:     return rate;
  30: }
  31:  
  32: public void setRate(int rate) {
  33:     Assert.assertTrue(rate > 0 && rate < 6);
  34:     this.rate = rate;
  35: }
  36:  
  37: public String getTitle() {
  38:     return title;
  39: }
  40:  
  41: public void setTitle(String title) {
  42:     this.title = title;
  43: }
  44:  
  45: public String getContent() {
  46:     return content;
  47: }
  48: public void setContent(String content) {
  49:     this.content = content;
  50: }
  51:  
  52: @ManyToOne(cascade = {CascadeType.ALL})
  53: @JoinColumn(name="book_id",
  54:         nullable = false,
  55:         updatable = false,
  56:         insertable = false)
  57: public Book getBook() {
  58:     return book;
  59: }
  60:  
  61: public void setBook(Book book) {
  62:     this.book = book;
  63: }
  64:  
  65: }

测试代码:

   1: package org.emoticon.library.manager;
   2:  
   3: import org.emoticon.core.test.DaoTestCase;
   4: import org.emoticon.library.model.Book;
   5: import org.emoticon.library.model.Comment;
   6:  
   7: public class BookManagerTest extends DaoTestCase {
   8:     private BookManager manager;
   9:     
  10:     private static final String commentTitle = "a good book";
  11:     
  12:     public void setManager(BookManager manager) {
  13:         this.manager = manager;
  14:     }
  15:     
  16:     public void testSave(){
  17:         Book entity = new Book();
  18:         entity.setTitle("thinking in java");
  19:         entity.setDescription("for newbie");
  20:         
  21:         Comment comment = new Comment();
  22:         comment.setTitle(commentTitle);
  23:         comment.setContent("I like it.");
  24:         comment.setRate(5);
  25:         
  26:         Comment comment2 = new Comment();
  27:         comment2.setTitle(commentTitle + "2");
  28:         comment2.setContent("I like it2.");
  29:         comment2.setRate(4);
  30:  
  31:         entity.addComment(comment);
  32:         entity.addComment(comment2);
  33:         
  34:         manager.save(entity);
  35:         assertNotNull(entity.getId());
  36:         entity = manager.get(entity.getId());
  37:         //assertEquals(entity.getComments().get(0).getTitle(), commentTitle);
  38:         assertNotNull(entity);
  39:         this.setComplete();
  40:     }
  41: }

这里需要注意:很多时候你在一对多list关联的时候,不真的需要indexcolumn来维护顺序。比如在线图书馆,如果没有indexcolumn也没问题。因为comment总是一条一条加的,那么indexcolumn那一列其实总不变。只有一下添加多个comment的时候,如上面代码,indexcolumn才会增加。comment的id本身就可以用来排序。

在线图书馆其实用不上indexcolumn, 实现的时候想错了,既然已经调通了,就记下来以后也许用得上。

posted on 2011-03-19 20:10 人在江湖 阅读(3345) 评论(0)  编辑  收藏 所属分类: hibernate

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