mappedby=？，后面的这个问号跟拥有方，以下是实例。

Role.java

package com.nbg.nuskin.oa.domain;import java.util.HashSet;
import java.util.Set;import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;/*** * * @author Administrator* */
@Entity
public class Role {private long id;private Set<Privilege> privileges = new HashSet<Privilege>();@Id@GeneratedValuepublic long getId() {return id;}public void setId(long id) {this.id = id;}//大家一定要注意这里，没有mappedby，拥有方是属于privilege的@ManyToManypublic Set<Privilege> getPrivileges() {return privileges;}public void setPrivileges(Set<Privilege> privileges) {this.privileges = privileges;}}

Privilege.java

package com.nbg.nuskin.oa.domain;import java.util.HashSet;
import java.util.Set;import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.OrderBy;@Entity
public class Privilege {private Long id;private Set<Role> roles = new HashSet<Role>();@Id@GeneratedValuepublic Long getId() {return id;}public void setId(Long id) {this.id = id;}//拥有方是Privilege.java@ManyToMany(mappedBy = "privileges")public Set<Role> getRoles() {return roles;}public void setRoles(Set<Role> roles) {this.roles = roles;}}

下面是RoleAction.java对Role的操作

package com.nbg.nuskin.oa.action;import java.util.HashSet;
import java.util.List;import javax.annotation.Resource;import com.nbg.nuskin.oa.domain.Privilege;
import com.nbg.nuskin.oa.domain.Role;
import com.nbg.nuskin.oa.service.PrivilegeService;
import com.nbg.nuskin.oa.service.RoleService;
import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.ModelDriven;public class RoleAction extends ActionSupport implements ModelDriven<Role> {private RoleService roleService;protected Role model = new Role();public RoleService getRoleService() {return roleService;}@Resource(name = "roleService")public void setRoleService(RoleService roleService) {this.roleService = roleService;}/*** 设置权限* * @return*/public String setPrivilege() {Role role = roleService.getById(model.getId());System.out.println(role.getName()+";"+role.getDescription());List<Privilege> privileges = privilegeService.getByIds(privilegeIds);role.setPrivileges(new HashSet<Privilege>(privileges));roleService.update(role);return "toList";}public Long[] getPrivilegeIds() {return privilegeIds;}public void setPrivilegeIds(Long[] privilegeIds) {this.privilegeIds = privilegeIds;}}

只有这样设置mappeby，在上面的action中才能够操作相应的privilege

mappedby原理：被拥有方改变，即拥有方主动关联操作关联关系；拥有方改变，不一定操作相关的关联关系

上面的mappedby如果设在roles这边，privileges就不会进行sql的update操作。