描述一下问题：
已知有两个表，一个是user表，一个是address,一（user）对多(address)的关系，在user的实体类里面写属性：

private List<Address> addressList = new ArrayList<Address>();public List<Address> getAddressList() {return addressList;}public void setAddressList(List<Address> addressList) {this.addressList = addressList;}

然后写了一个测试方法，根据用户的编号查询地址信息，一个用户对应多个地址。
配置如下：

<resultMap type="User" id="userAddMap"><id property="id" column="id"/><result property="userName" column="userName"/><result property="userCode" column="userCode"/><result property="userPassword" column="userPassword"/><result property="gender" column="gender"/><result property="birthday" column="birthday"/><result property="phone" column="phone"/><result property="address" column="address"/><result property="userRole" column="userRole"/><result property="createdBy" column="createdBy"/><result property="creationDate" column="creationDate"/><result property="modifyBy" column="modifyBy"/><result property="modifyDate" column="modifyDate"/><result property="roleName" column="roleName"/><collection property="addressList" ofType="Address"><id property="aid" column="id"/><result property="contact" column="contact"/><result property="addressDesc" column="addressDesc"/><result property="postCode" column="postCode"/><result property="tel" column="tel"/><result property="createdBy" column="createdBy"/><result property="creationDate" column="creationDate"/><result property="modifyBy" column="modifyBy"/><result property="modifyDate" column="modifyDate"/><result property="userId" column="userId"/></collection></resultMap>

sql映射如下：

<select id="findUserByidAndAddress" parameterType="Integer" resultMap="userAddMap">SELECT u.*,a.id,a.contact,a.addressdesc,a.postCodeFROM smbms_user u,smbms_address a WHERE u.id = a.userid AND  u.id = #{id} </select>

看起来没有任何问题吧，写了个测试方法：

@Testpublic void findUserByidAndAddress(){SqlSession sqlSession = utils.getSqlSession();User user = sqlSession.getMapper(IUserDao.class).findUserByidAndAddress(1);List<Address> addressList = user.getAddressList();for (Address address : addressList) {System.out.println(address.getAddressDesc());}}

运行结果如图所示：

可是数据库中却有三条记录：

经过自己琢磨，不行。
然后上网查了下，原来是数据库中两个表中的主键都是id,如果配置collection一对多关联的话需要改别名，我就试着改了下，发现，可以了。
改过之后的映射文件如下：

<resultMap type="User" id="userAddMap"><id property="id" column="id"/><result property="userName" column="userName"/><result property="userCode" column="userCode"/><result property="userPassword" column="userPassword"/><result property="gender" column="gender"/><result property="birthday" column="birthday"/><result property="phone" column="phone"/><result property="address" column="address"/><result property="userRole" column="userRole"/><result property="createdBy" column="createdBy"/><result property="creationDate" column="creationDate"/><result property="modifyBy" column="modifyBy"/><result property="modifyDate" column="modifyDate"/><result property="roleName" column="roleName"/><collection property="addressList" ofType="Address"><id property="aid" column="aid"/><result property="contact" column="contact"/><result property="addressDesc" column="addressDesc"/><result property="postCode" column="postCode"/><result property="tel" column="tel"/><result property="createdBy" column="createdBy"/><result property="creationDate" column="creationDate"/><result property="modifyBy" column="modifyBy"/><result property="modifyDate" column="modifyDate"/><result property="userId" column="userId"/></collection></resultMap>

sql语句如下：

 <select id="findUserByidAndAddress" parameterType="Integer" resultMap="userAddMap">SELECT u.*,a.id as aid,a.contact,a.addressdesc,a.postCodeFROM smbms_user u,smbms_address a WHERE u.id = a.userid AND  u.id = #{id} </select>

注意：resultMap中的property对应的是实体类里面的属性，而column严格意义上来说对应的是结果集里面的列名，而不是数据库中的列，比如起别名的话就对应的是别名，不是原来的列，切记切记！！！
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