在abator中可生成iBatis的代码。其中，Sql_map中带有的两个函数是：
updateByPrimaryKeySelective
updateByPrimaryKey
前者只是更新新的model中不为空的字段。
后者则会将为空的字段在数据库中置为NULL。

Labor labor = new Labor();
labor.setIdentitycard(identitycard);
labor.setName(name);
labor.setDepartmentid(Integer.parseInt("1"));
labor.setEmployeenumber(Integer.parseInt("1006"));
labor.setLeadernumberid(Integer.parseInt("1001"));

result = laborAO.doSave(labor, "updateByIdentitycard");
if (!result.isSuccess()) {
    return INPUT;
} else {
    System.out.println("message : insert " + name + " . \n");
    return SUCCESS;
}

如果DAO中使用的是updateByPrimaryKeySelective，则按照不为空的labor值去更新。
如果使用updateByPrimaryKey，这在labor中未定义的字段更新后就没有了。
从SQL语句上分析，二者的不同：

<update id="updateByPrimaryKeySelective" parameterClass="com.sk.maxdrive.dal.model.Labor" >
    <!--
      WARNING - @ibatorgenerated
      This element is automatically generated by Apache iBATIS Ibator, do not modify.
      This element was generated on Thu Sep 01 13:55:37 CST 2011.
    -->
    update labor
    <dynamic prepend="set" >
      <isNotNull prepend="," property="name" >
        NAME = #name:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="tagid" >
        TAGID = #tagid:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="departmentid" >
        DEPARTMENTID = #departmentid:INTEGER#
      </isNotNull>
      <isNotNull prepend="," property="duty" >
        DUTY = #duty:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="employeenumber" >
        EMPLOYEENUMBER = #employeenumber:INTEGER#
      </isNotNull>
      <isNotNull prepend="," property="leadernumberid" >
        LEADERNUMBERID = #leadernumberid:INTEGER#
      </isNotNull>
      <isNotNull prepend="," property="home" >
        HOME = #home:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="address" >
        ADDRESS = #address:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="emergencynumber" >
        EMERGENCYNUMBER = #emergencynumber:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="emergencycontact" >
        EMERGENCYCONTACT = #emergencycontact:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="hoursetel" >
        HOURSETEL = #hoursetel:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="postcode" >
        POSTCODE = #postcode:INTEGER#
      </isNotNull>
      <isNotNull prepend="," property="cellphone" >
        CELLPHONE = #cellphone:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="email" >
        EMAIL = #email:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="resume" >
        RESUME = #resume:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="employeedate" >
        EMPLOYEEDATE = #employeedate:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="headpic" >
        HEADPIC = #headpic:VARCHAR#
      </isNotNull>
      <isNotNull prepend="," property="bankaccount" >
        BANKACCOUNT = #bankaccount:VARCHAR#
      </isNotNull>
    </dynamic>
    where IDENTITYCARD = #identitycard:VARCHAR#
  </update>

一系列的isNull判断

<update id="updateByPrimaryKey" parameterClass="com.sk.maxdrive.dal.model.Labor" >
    <!--
      WARNING - @ibatorgenerated
      This element is automatically generated by Apache iBATIS Ibator, do not modify.
      This element was generated on Thu Sep 01 13:55:37 CST 2011.
    -->
    update labor
    set NAME = #name:VARCHAR#,
      TAGID = #tagid:VARCHAR#,
      DEPARTMENTID = #departmentid:INTEGER#,
      DUTY = #duty:VARCHAR#,
      EMPLOYEENUMBER = #employeenumber:INTEGER#,
      LEADERNUMBERID = #leadernumberid:INTEGER#,
      HOME = #home:VARCHAR#,
      ADDRESS = #address:VARCHAR#,
      EMERGENCYNUMBER = #emergencynumber:VARCHAR#,
      EMERGENCYCONTACT = #emergencycontact:VARCHAR#,
      HOURSETEL = #hoursetel:VARCHAR#,
      POSTCODE = #postcode:INTEGER#,
      CELLPHONE = #cellphone:VARCHAR#,
      EMAIL = #email:VARCHAR#,
      RESUME = #resume:VARCHAR#,
      EMPLOYEEDATE = #employeedate:VARCHAR#,
      HEADPIC = #headpic:VARCHAR#,
      BANKACCOUNT = #bankaccount:VARCHAR#
    where IDENTITYCARD = #identitycard:VARCHAR#
  </update>

没有判断，直接加载