第一次写博客，只想把工作中遇到的问题记下来。
最近做了一个二次开发的改造，改完之后被告知数据表主键根据需求需要用复合主键，因为本人菜鸟一枚，复合主键从未用过，只能靠度娘
网上给出的复合主键映射大致就两种
第一种：将复合主键对应的属性与实体其他普通属性放在一起
/*实体类.复合主键必须实现Serialzable接口*/public class User implements Serialzable{private static final long serialVersionUID=1L;//版本之间的兼容，数值自己定义private String id;private String name;private int age;public User(){}public String getId(){return id;}public void setId(String id){this.id=id;}public String getName(){return name;}public void setName(String name){this.name=name;}public int getAge(){return age;}public void setAge(int age){this.age=age;}public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((id == null) ? 0 : id.hashCode()); result = prime * result + ((name == null) ? 0 : name.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; People other = (People) obj; if (id == null) { if (other.id != null) return false; } else if (!id.equals(other.id)) return false; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; return true; } } 注意：复合主键实体类需要重写hashCode()和equals（）方法
User..hbm.xml;
true
第二种方式：将主键属性提取到一个主键类中，实体类只需要包涵主键类的一个引用
/*主键类*/public class UserPK implements Serializable{private String name;private String id;public String getId(){return id;}public void setId(){this.id=id;}public String getName(){return name;}public void setName(){this.name=name;}public boolean equals (Object obj) { if (null == obj) return false; if (!(obj instanceof com.huateng.po.UserPK )) return false; else { com.huateng.po.UserPK mObj = (com.huateng.po.UserPK ) obj; if (null != this.getId() && null != mObj.getId()) { if (!this.getId().equals(mObj.getId())) { return false; } } else { return false; } if (null != this.getName() && null != mObj.getName()) { if (!this.getName().equals(mObj.getName())) { return false; } } else { return false; } return true; } } public int hashCode () { if (Integer.MIN_VALUE == this.hashCode) { StringBuilder sb = new StringBuilder(); if (null != this.getId()) { sb.append(this.getId().hashCode()); sb.append(":"); } else { return super.hashCode(); } if (null != this.getName()) { sb.append(this.getName().hashCode()); sb.append(":"); } else { return super.hashCode(); } this.hashCode = sb.toString().hashCode(); } return this.hashCode; }}/*实体类*/public class User implements Serializable{private static final long serialVersionUID = 1L; private UserPK id;private int age; public UserPK getId() { return id; } public UserPK setId() { this.id=id; }public int getAge(){return age;}public void setAge(){this.age=age;}}
User.hbm.xml
以上仅仅只能当作参考，具体的还要根据实际情况修改以下送上我工作中的代码 true
/* @(#) * * * * Modify Information: * ============================================================================= * Author Date Description * ------------ ---------- --------------------------------------------------- * 徐志诚 2016-5-18 first release * * * Copyright Notice: * ============================================================================= * Copyright 2016 Huateng Software, Inc. All rights reserved. * * This software is the confidential and proprietary information of * Shanghai HUATENG Software Co., Ltd. ("Confidential Information"). * You shall not disclose such Confidential Information and shall use it * only in accordance with the terms of the license agreement you entered * into with Huateng. * * Warning: * ============================================================================= * */package com.huateng.po;import java.io.Serializable;/** * Title: * * Description: * * Copyright: Copyright (c) 2016-5-18 * * Company: Shanghai Huateng Software Systems Co., Ltd. * * * * @version 1.0 *///@SuppressWarnings("serial")public class Tblvatrule implements Serializable{ private static final long serialVersionUID = 1L; public static String REF ="Tblvatrule"; public static String PROP_ORACLE_GL="oraclegl"; public static String PROP_GL_DESC="gldesc"; public static String PROP_DC_FLAG="dcflag"; public static String PROP_TAX_RATE="taxrate"; public static String PROP_TAN_NUM="tannum"; public static String PROP_EFF_DATE="effdate"; public static String PROP_status="status"; public static String PROP_MODIFY_TLR="modifytlr"; public static String PROP_MODIFY_TIME="modifytime"; public static String PROP_AUTH_TLR="authtlr"; public static String PROP_AUTH_TIME="authtime"; public static String PROP_TAX_GL="taxgl"; public static String PROP_TAX_CODE="taxcode"; public static String PROP_ID="id"; public Tblvatrule(){ } public Tblvatrule(com.huateng.po.TblvatruleTmpPK id,java.lang.String oraclegl,java.lang.String dcflag){ this.setId(id); this.setOraclegl(oraclegl); this.setDcflag(dcflag); initialize(); } protected void initialize () {} private com.huateng.po.TblvatruleTmpPK id;/** * @return the id */ public com.huateng.po.TblvatruleTmpPK getId() { return id; } /** * @param id the id to set */ public void setId(com.huateng.po.TblvatruleTmpPK id) { this.id = id; }private java.lang.String oraclegl; //账号private java.lang.String gldesc; //账户描述private java.lang.String dcflag; //借贷标识private java.lang.String taxrate; //税率private java.lang.String txnnum; //交易码private java.lang.String effdate; //生效日期private java.lang.String status; //状态private java.lang.String modifytlr; //录入操作员private java.lang.String modifytime; //录入时间private java.lang.String authtlr; //审核操作员private java.lang.String authtime; //审核时间private java.lang.String taxgl; //增值税账号private java.lang.String taxcode; //增值税代码private int hashCode = Integer.MIN_VALUE;/** * @return the taxgl */public java.lang.String getTaxgl() { return taxgl;}/** * @param taxgl the taxgl to set */public void setTaxgl(java.lang.String taxgl) { this.taxgl = taxgl;}/** * @return the taxcode */public java.lang.String getTaxcode() { return taxcode;}/** * @param taxcode the taxcode to set */public void setTaxcode(java.lang.String taxcode) { this.taxcode = taxcode;}/** * @return the oraclegl */public java.lang.String getOraclegl() { return oraclegl;}/** * @param oraclegl the oraclegl to set */public void setOraclegl(java.lang.String oraclegl) { this.oraclegl = oraclegl;}/** * @return the gldesc */public java.lang.String getGldesc() { return gldesc;}/** * @param gldesc the gldesc to set */public void setGldesc(java.lang.String gldesc) { this.gldesc = gldesc;}/** * @return the dcflag */public java.lang.String getDcflag() { return dcflag;}/** * @param dcflag the dcflag to set */public void setDcflag(java.lang.String dcflag) { this.dcflag = dcflag;}/** * @return the taxrate */public java.lang.String getTaxrate() { return taxrate;}/** * @param taxrate the taxrate to set */public void setTaxrate(java.lang.String taxrate) { this.taxrate = taxrate;}/** * @return the txnnum */public java.lang.String getTxnnum() { return txnnum;}/** * @param txnnum the txnnum to set */public void setTxnnum(java.lang.String txnnum) { this.txnnum = txnnum;}/** * @return the effdate */public java.lang.String getEffdate() { return effdate;}/** * @param effdate the effdate to set */public void setEffdate(java.lang.String effdate) { this.effdate = effdate;}/** * @return the status */public java.lang.String getStatus() { return status;}/** * @param status the status to set */public void setStatus(java.lang.String status) { this.status = status;}/** * @return the modifytlr */public java.lang.String getModifytlr() { return modifytlr;}/** * @param modifytlr the modifytlr to set */public void setModifytlr(java.lang.String modifytlr) { this.modifytlr = modifytlr;}/** * @return the modifytimel */public java.lang.String getModifytime() { return modifytime;}/** * @param modifytimel the modifytimel to set */public void setModifytime(java.lang.String modifytime) { this.modifytime = modifytime;}/** * @return the authtlr */public java.lang.String getAuthtlr() { return authtlr;}/** * @param authtlr the authtlr to set */public void setAuthtlr(java.lang.String authtlr) { this.authtlr = authtlr;}/** * @return the authtime */public java.lang.String getAuthtime() { return authtime;}/** * @param authtime the authtime to set */public void setAuthtime(java.lang.String authtime) { this.authtime = authtime;}public boolean equals (Object obj) { if (null == obj) return false; if (!(obj instanceof com.huateng.po.Tblvatrule)) return false; else { com.huateng.po.Tblvatrule tvrt = (com.huateng.po.Tblvatrule) obj; if (null == this.getId() || null == tvrt.getId()) return false; else return (this.getId().equals(tvrt.getId())); }}public int hashCode () { if (Integer.MIN_VALUE == this.hashCode) { if (null == this.getId()) return super.hashCode(); else { java.lang.String hashStr = this.getClass().getName() + ":" + this.getId().hashCode(); this.hashCode = hashStr.hashCode(); } } return this.hashCode;}public java.lang.String toString () { return super.toString();}} /* @(#) * * Project:OCBCServer * * Modify Information: * ============================================================================= * Author Date Description * ------------ ---------- --------------------------------------------------- * 徐志诚 2016-6-12 first release * * * Copyright Notice: * ============================================================================= * Copyright 2016 Huateng Software, Inc. All rights reserved. * * This software is the confidential and proprietary information of * Shanghai HUATENG Software Co., Ltd. ("Confidential Information"). * You shall not disclose such Confidential Information and shall use it * only in accordance with the terms of the license agreement you entered * into with Huateng. * * Warning: * ============================================================================= * */package com.huateng.po;import java.io.Serializable;/** * Title: * * Description: * * Copyright: Copyright (c) 2016-6-12 * * Company: Shanghai Huateng Software Systems Co., Ltd. * * @author 徐志诚 * * @version 1.0 */@SuppressWarnings("serial")public class TblvatrulePK implements Serializable{ protected int hashCode = Integer.MIN_VALUE; private java.lang.String oraclegl; //账号 private java.lang.String dcflag; //借贷标识 public TblvatrulePK(){ } public TblvatrulePK(java.lang.String oraclegl,java.lang.String dcflag){ this.setOraclegl(oraclegl); this.setDcflag(dcflag); } /** * @return the oraclegl */ public java.lang.String getOraclegl() { return oraclegl; } /** * @param oraclegl the oraclegl to set */ public void setOraclegl(java.lang.String oraclegl) { this.oraclegl = oraclegl; } /** * @return the dcflag */ public java.lang.String getDcflag() { return dcflag; } /** * @param dcflag the dcflag to set */ public void setDcflag(java.lang.String dcflag) { this.dcflag = dcflag; } public boolean equals (Object obj) { if (null == obj) return false; if (!(obj instanceof com.huateng.po.TblvatrulePK)) return false; else { com.huateng.po.TblvatrulePK mObj = (com.huateng.po.TblvatrulePK) obj; if (null != this.getOraclegl() && null != mObj.getOraclegl()) { if (!this.getOraclegl().equals(mObj.getOraclegl())) { return false; } } else { return false; } if (null != this.getDcflag() && null != mObj.getDcflag()) { if (!this.getDcflag().equals(mObj.getDcflag())) { return false; } } else { return false; } return true; } } public int hashCode () { if (Integer.MIN_VALUE == this.hashCode) { StringBuilder sb = new StringBuilder(); if (null != this.getOraclegl()) { sb.append(this.getOraclegl().hashCode()); sb.append(":"); } else { return super.hashCode(); } if (null != this.getDcflag()) { sb.append(this.getDcflag().hashCode()); sb.append(":"); } else { return super.hashCode(); } this.hashCode = sb.toString().hashCode(); } return this.hashCode; }} true
总结：复合主键是一个指一个主键是有一个以上字段组成,
当一个主键字段无法确保其唯一性时，需要其他字段一起形成唯一性，
优点是唯一性得到保证，缺点是影响查询和修改的效率。