联合主键的注解使用:
1.使用@Id来申明主键,同时将该主键的类用@Embeddable设置
如:
//联合主键对象类 /* * 注意在hashcode和equals方法的作用,在系统中所有相同的hashcode值得对象都存到一个数组中, * 这个数组的么一个元素都是一个队列,然后当我们需哟啊找到每个对象时,就查找该对象的hashcode进而找出该对象的 * 在数组中的位置,然后再取出队列遍历用每个对象的equals方法判断该对象是否与查找的对象相等,知直到找到相等的 * 对象,否则将会出现空指针异常 */ @Embeddable public class TeacherPK implements Serializable { private int id; private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getId() { return id; } public void setId(int id) { this.id = id; } @Override public boolean equals(Object obj) { if(obj instanceof TeacherPK){ TeacherPK pk = (TeacherPK) obj; if(this.id == pk.getId()&&this.name.equals(pk.getName())){ return true; } } return false; } @Override public int hashCode() { return this.name.hashCode(); } } public class Teacher { private TeacherPK pk; @Id public TeacherPK getPk() { return pk; } public void setPk(TeacherPK pk) { this.pk = pk; } private String title; public void setTitle(String title) { this.title = title; } public String getTitle() { return title; } }
2.使用@Id将多个属性申明为主键,另外在该类的上使用@IdClass(value="你需要符合的类")
如:
@IdClass(value="TeacherPK.class") public class Teacher{ private int id; private String name; private String title; @Id public int getId() { return id; } @Id public String getName() { return name; } public void setId(int id) { this.id = id; } public void setName(String name) { this.name = name; } public void setTitle(String title) { this.title = title; } public String getTitle() { return title; } } public class TeacherPK implements Serializable { private int id; private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getId() { return id; } public void setId(int id) { this.id = id; } @Override public boolean equals(Object obj) { if(obj instanceof TeacherPK){ TeacherPK pk = (TeacherPK) obj; if(this.id == pk.getId()&&this.name.equals(pk.getName())){ return true; } } return false; } @Override public int hashCode() { return this.name.hashCode(); } }
3.将主键属性设置@EmbeddedId申明即可,主键类可不申明任何注解
如:
//主键类 public class TeacherPK implements Serializable { private int id; private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getId() { return id; } public void setId(int id) { this.id = id; } @Override public boolean equals(Object obj) { if(obj instanceof TeacherPK){ TeacherPK pk = (TeacherPK) obj; if(this.id == pk.getId()&&this.name.equals(pk.getName())){ return true; } } return false; } @Override public int hashCode() { return this.name.hashCode(); } } public class Teacher { private TeacherPK pk; @EmbeddedId public TeacherPK getPk() { return pk; } public void setPk(TeacherPK pk) { this.pk = pk; } private String title; public void setTitle(String title) { this.title = title; } public String getTitle() { return title; } }
这三种方式各有各的好处,个人认为在开发中第三种比较常用。
注意:联合主键不会生成新的表。