ibaitis 级联查询
使用iBatis开发已经有一年了，这一年来不管愿意不愿意，喜欢不喜欢，都得用，想用Hibernate不行。
随着对iBatis的熟悉，渐渐发现初次接触的人因为不能很好的掌握iBatis使用的方法而对其有一些偏激的看法。
1、iBatis的是用来自由写SQL的，对SQL语句的简单的封装，相当于在JDBC上加了层外壳。
我认为，iBatis的目标是简化JDBC的操作，对SQL的查询结果做了很好的映射封装，这样查询的结果就形成了一个java对象、集合、或者Map等。这样的数据结构相比JDBC结果集的处理是一个质的飞跃。
iBatis虽然支持随意的SQL查询，并且对查询结果集也没有什么特别限制，最懒惰的是定义查询结果集类型为map。但是，这并不是 iBatis设计者的本意，我认为，在使用iBatis的时候，尽可能写通用的增删改差sql，然后通过通过这些sql所对应DAO方法的组合，来实现各 种业务，而不是写很多特殊的sql、甚至存储过程。当你在更换数据库的时候，移植这些特殊sql和过程就是一件很困难的事情。
2、iBatis映射太麻烦，表字段和实体（Entity，也有人称POJO）对应比较麻烦，不够直观，开发困难。
其实，最好的做法就是使用数据库表字段名作为实体的属性名，这样完全对应起来，问题就解决了。并且，可以写个工具，从数据库生成POJO和SQLMap、DAO、Service等等。这样可以极大提高效率，我就这么做的。
3、iBatis分页是内存分页，假分页
的确如此，对于小数据量是够用了，对于大数据量，这是不可接受的。因此可以通过动态SqL来拼装分页查询Sql。
<
dynamic prepend=""
>
< isNotNull property ="_start" >
< isNotNull property ="_size" >
limit #_start#, #_size#
</ isNotNull >
</ isNotNull >
</ dynamic >
< isNotNull property ="_start" >
< isNotNull property ="_size" >
limit #_start#, #_size#
</ isNotNull >
</ isNotNull >
</ dynamic >
4、iBatis无法做成Hibernate那样的关连查询、级联保存、级联删除。
iBatis可以做到，而且实现很灵活方便。但是比Hibernate操作更容易，也很好理解。这里面对结果集映射类型也很讲究。
<
resultMap
id
="result_base"
class
="Channel"
>
< result property ="id" column ="id" />
< result property ="stationid" column ="stationid" />
< result property ="remark" column ="remark" />
< result property ="status" column ="status" />
</ resultMap >
< resultMap id ="result" class ="Channel" extends ="channel.result_base" >
< result property ="cfgList" column ="id" select ="videoregxp.findByChannelId" />
</ resultMap >
< result property ="id" column ="id" />
< result property ="stationid" column ="stationid" />
< result property ="remark" column ="remark" />
< result property ="status" column ="status" />
</ resultMap >
< resultMap id ="result" class ="Channel" extends ="channel.result_base" >
< result property ="cfgList" column ="id" select ="videoregxp.findByChannelId" />
</ resultMap >
<
resultMap
id
="result_base"
class
="Videoregxp"
>
< result property ="id" column ="id" />
< result property ="lmid" column ="lmid" />
< result property ="name" column ="name" />
< result property ="cname" column ="cname" />
< result property ="sortnum" column ="sortnum" />
< result property ="remark" column ="remark" />
</ resultMap >
< resultMap id ="result" class ="Videoregxp" extends ="videoregxp.result_base" >
< result property ="regex" column ="id" select ="regexpar.findByVideoregxpId" />
</ resultMap >
< result property ="id" column ="id" />
< result property ="lmid" column ="lmid" />
< result property ="name" column ="name" />
< result property ="cname" column ="cname" />
< result property ="sortnum" column ="sortnum" />
< result property ="remark" column ="remark" />
</ resultMap >
< resultMap id ="result" class ="Videoregxp" extends ="videoregxp.result_base" >
< result property ="regex" column ="id" select ="regexpar.findByVideoregxpId" />
</ resultMap >
/**
* 保存一个视频信息，级联保存相关的剧集和视频分段文件
*
* @param videoinfo 视频信息对象
* @return 返回保存后的对象
*/
public Videoinfo saveVideoinfoWithCascade(Videoinfo videoinfo) {
videoinfoDAO.saveVideoinfo(videoinfo);
for (Juji juji : videoinfo.getJujiList()) {
juji.setVideoid(videoinfo.getId());
jujiDAO.saveJuji(juji);
for (Secfiles file : juji.getSecfileList()) {
file.setSegmentid(juji.getId());
secfilesDAO.saveSecfiles(file);
}
}
return videoinfo;
}
* 保存一个视频信息，级联保存相关的剧集和视频分段文件
*
* @param videoinfo 视频信息对象
* @return 返回保存后的对象
*/
public Videoinfo saveVideoinfoWithCascade(Videoinfo videoinfo) {
videoinfoDAO.saveVideoinfo(videoinfo);
for (Juji juji : videoinfo.getJujiList()) {
juji.setVideoid(videoinfo.getId());
jujiDAO.saveJuji(juji);
for (Secfiles file : juji.getSecfileList()) {
file.setSegmentid(juji.getId());
secfilesDAO.saveSecfiles(file);
}
}
return videoinfo;
}
/**
* 删除指定标识的一个栏目
*
* @param id 栏目标识
*/
public void deleteChannelById(Long id) {
//todo:做可行性校验,以及级联删除等操作，并做业务特殊需求校验
Channel ch = channelDAO.findChannelById(id);
for (Videoregxp v : ch.getCfgList()) {
regexparDAO.deleteRegexparByCfgId(v.getId());
}
videoregxpDAO.deleteVideoregxpByLmId(ch.getId());
channelDAO.deleteChannelById(id);
}
* 删除指定标识的一个栏目
*
* @param id 栏目标识
*/
public void deleteChannelById(Long id) {
//todo:做可行性校验,以及级联删除等操作，并做业务特殊需求校验
Channel ch = channelDAO.findChannelById(id);
for (Videoregxp v : ch.getCfgList()) {
regexparDAO.deleteRegexparByCfgId(v.getId());
}
videoregxpDAO.deleteVideoregxpByLmId(ch.getId());
channelDAO.deleteChannelById(id);
}
5、iBatis延迟加载好像有问题，本人现在不能确信。
6、iBatis用熟悉了和Hibernate一样容易，通过自己开发工具，可以极大提高开发效率。我会在附件贡献出我的代码生成工具。
7、iBatis的cache缓存没感觉到有多大优势，也没感觉性能的提升。
8、iBatis的动态SQL功能强大，Map参数更能获取最大的灵活性，这是Hibernate和其他持久化框架所无法相比的。
<
select
id
="findByParams"
parameterClass
="map"
resultMap
="channel.result"
>
< include refid ="sql_select" />
< include refid ="sql_where" />
</ select >
< include refid ="sql_select" />
< include refid ="sql_where" />
</ select >
/**
* 根据动态条件查询栏目
*
* @param map 参数map
* @return 查询结果集
*/
public List<Channel> findChannelByParams(Map map) {
return getSqlMapClientTemplate().queryForList( "channel.findByParams" , map);
}
* 根据动态条件查询栏目
*
* @param map 参数map
* @return 查询结果集
*/
public List<Channel> findChannelByParams(Map map) {
return getSqlMapClientTemplate().queryForList( "channel.findByParams" , map);
}
但是map参数也缺乏明确性，使用者无法清楚知道map参数里面究竟可以传什么类型，但是使用者可以通过查看sqlMap进一步获得对参数的详细认识，比如上面的完整SQLMap片段是：
<!--
动态条件分页查询 -->
< sql id ="sql_count" >
select count(*)
</ sql >
< sql id ="sql_select" >
select *
</ sql >
< sql id ="sql_where" >
from channel
< dynamic prepend ="where" >
< isNotNull prepend ="and" property ="stationid" >
stationid = #stationid#
</ isNotNull >
< isNotEmpty prepend ="and" property ="name" >
name like '%$name$%'
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="url" >
url like '%$url$%'
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="regxp" >
regxp like '$regxp$%'
</ isNotEmpty >
< isNotNull prepend ="and" property ="encoding" >
encoding = #encoding#
</ isNotNull >
< isNotEmpty prepend ="and" property ="_timeout_ge" >
<![CDATA[
timeout >= #_timeout_ge#
]]>
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_timeout_lt" >
<![CDATA[
timeout < #_timeout_lt#
]] >
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_maxrow_ge" >
<![CDATA[
maxrow >= #_maxrow_ge#
]]>
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_maxrow_lt" >
<![CDATA[
maxrow < #_maxrow_lt#
]] >
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_start_ge" >
<![CDATA[
start >= #_start_ge#
]]>
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_start_lt" >
<![CDATA[
start < #_start_lt#
]] >
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="pagereg" >
pagereg like '%$pagereg$%'
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="kind" >
kind = #kind#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="mapname" >
mapname = #mapname#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="replaceb" >
replaceb = #replaceb#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="replacea" >
replacea = #replacea#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="ifredo" >
ifredo = #ifredo#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="fenbianlv" >
fenbianlv = #fenbianlv#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_size_ge" >
<![CDATA[
size >= #_size_ge#
]]>
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_size_lt" >
<![CDATA[
size < #_size_lt#
]] >
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="remark" >
remark like '%$remark$%'
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="status" >
status = #status#
</ isNotEmpty >
</ dynamic >
< dynamic prepend="" >
< isNotNull property ="_start" >
< isNotNull property ="_size" >
limit #_start#, #_size#
</ isNotNull >
</ isNotNull >
</ dynamic >
</ sql >
< select id ="findByParamsForCount" parameterClass ="map" resultClass ="int" >
< include refid ="sql_count" />
< include refid ="sql_where" />
</ select >
< select id ="findByParams" parameterClass ="map" resultMap ="channel.result" >
< include refid ="sql_select" />
< include refid ="sql_where" />
</ select >
< sql id ="sql_count" >
select count(*)
</ sql >
< sql id ="sql_select" >
select *
</ sql >
< sql id ="sql_where" >
from channel
< dynamic prepend ="where" >
< isNotNull prepend ="and" property ="stationid" >
stationid = #stationid#
</ isNotNull >
< isNotEmpty prepend ="and" property ="name" >
name like '%$name$%'
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="url" >
url like '%$url$%'
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="regxp" >
regxp like '$regxp$%'
</ isNotEmpty >
< isNotNull prepend ="and" property ="encoding" >
encoding = #encoding#
</ isNotNull >
< isNotEmpty prepend ="and" property ="_timeout_ge" >
<![CDATA[
timeout >= #_timeout_ge#
]]>
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_timeout_lt" >
<![CDATA[
timeout < #_timeout_lt#
]] >
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_maxrow_ge" >
<![CDATA[
maxrow >= #_maxrow_ge#
]]>
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_maxrow_lt" >
<![CDATA[
maxrow < #_maxrow_lt#
]] >
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_start_ge" >
<![CDATA[
start >= #_start_ge#
]]>
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_start_lt" >
<![CDATA[
start < #_start_lt#
]] >
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="pagereg" >
pagereg like '%$pagereg$%'
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="kind" >
kind = #kind#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="mapname" >
mapname = #mapname#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="replaceb" >
replaceb = #replaceb#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="replacea" >
replacea = #replacea#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="ifredo" >
ifredo = #ifredo#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="fenbianlv" >
fenbianlv = #fenbianlv#
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_size_ge" >
<![CDATA[
size >= #_size_ge#
]]>
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="_size_lt" >
<![CDATA[
size < #_size_lt#
]] >
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="remark" >
remark like '%$remark$%'
</ isNotEmpty >
< isNotEmpty prepend ="and" property ="status" >
status = #status#
</ isNotEmpty >
</ dynamic >
< dynamic prepend="" >
< isNotNull property ="_start" >
< isNotNull property ="_size" >
limit #_start#, #_size#
</ isNotNull >
</ isNotNull >
</ dynamic >
</ sql >
< select id ="findByParamsForCount" parameterClass ="map" resultClass ="int" >
< include refid ="sql_count" />
< include refid ="sql_where" />
</ select >
< select id ="findByParams" parameterClass ="map" resultMap ="channel.result" >
< include refid ="sql_select" />
< include refid ="sql_where" />
</ select >
通过上面的映射，我们可以很清楚的看到，SQL的片段得到了重用，分页很优雅，统计和全功能查询也非常强大，相比hibernate，有过之而无不及，当然如果你不会这么用，那就麻烦多了。
9、我认为，iBatis应该尽量使用单表增删改差业务来组合功能更为强大的业务操作。但并不排斥使用多表关联进行查询，多表关联查询，结果集往往需要定义新的JavaBean来进行存储，但也可以简单的返回一个Map来存储结果集。
<!--
动态条件分页查询 -->
< sql id ="sql_count" >
select count(a.*)
</ sql >
< sql id ="sql_select" >
select a.id vid,
a.img imgurl,
a.img_s imgfile,
b.vfilename vfilename,
c.id sid,
c.url url,
c.filename filename,
c.status status
</ sql >
< sql id ="sql_where" >
From secfiles c, juji b, videoinfo a
where
a.id = b. videoid
and b.id = c.segmentid
and c.status = 0
< dynamic prepend="" >
< isNotNull property ="_start" >
< isNotNull property ="_size" >
limit #_start#, #_size#
</ isNotNull >
</ isNotNull >
</ dynamic >
</ sql >
<!-- 返回没有下载的记录总数 -->
< select id ="getUndownFilesForCount" parameterClass ="map" resultClass ="int" >
< include refid ="sql_count" />
< include refid ="sql_where" />
</ select >
<!-- 返回没有下载的记录 -->
< select id ="getUndownFiles" parameterClass ="map" resultClass ="java.util.HashMap" >
< include refid ="sql_select" />
< include refid ="sql_where" />
</ select >
< sql id ="sql_count" >
select count(a.*)
</ sql >
< sql id ="sql_select" >
select a.id vid,
a.img imgurl,
a.img_s imgfile,
b.vfilename vfilename,
c.id sid,
c.url url,
c.filename filename,
c.status status
</ sql >
< sql id ="sql_where" >
From secfiles c, juji b, videoinfo a
where
a.id = b. videoid
and b.id = c.segmentid
and c.status = 0
< dynamic prepend="" >
< isNotNull property ="_start" >
< isNotNull property ="_size" >
limit #_start#, #_size#
</ isNotNull >
</ isNotNull >
</ dynamic >
</ sql >
<!-- 返回没有下载的记录总数 -->
< select id ="getUndownFilesForCount" parameterClass ="map" resultClass ="int" >
< include refid ="sql_count" />
< include refid ="sql_where" />
</ select >
<!-- 返回没有下载的记录 -->
< select id ="getUndownFiles" parameterClass ="map" resultClass ="java.util.HashMap" >
< include refid ="sql_select" />
< include refid ="sql_where" />
</ select >
在上面，我们的结果集返回为resultClass="java.util.HashMap"，这时候，需要根据字
段的名称来取值，值类型为Object，key类型为String，这点要注意了：
public List<Map<String,Object>> findUndownFiles(Map map) {
return getSqlMapClientTemplate().queryForList( "secfiles.getUndownFiles" , map);
}
return getSqlMapClientTemplate().queryForList( "secfiles.getUndownFiles" , map);
}
public
void test_findUndownFiles() {
List<Map<String, Object>> co = ser.findUndownFiles( new HashMap());
StringBuilder s = new StringBuilder();
for (Map<String, Object> map : co) {
System.out.println( "---------------------------" );
for (Map.Entry<String, Object> entry : map.entrySet()) {
System.out.print(entry.getKey()+ "\t" );
System.out.println(entry.getValue());
}
}
}
List<Map<String, Object>> co = ser.findUndownFiles( new HashMap());
StringBuilder s = new StringBuilder();
for (Map<String, Object> map : co) {
System.out.println( "---------------------------" );
for (Map.Entry<String, Object> entry : map.entrySet()) {
System.out.print(entry.getKey()+ "\t" );
System.out.println(entry.getValue());
}
}
}
打印结果：
---------------------------
sid 1
vfilename 200905252009235799
url http://d18.v.iask.com/f/1/f47817a394730dc682e660b943e84cc41006606.flv
status 0
filename 200905252009235799-00.flv
imgfile 200905252009234399.jpg
vid 1
imgurl http://p4.v.iask.com/95/595/1757503_1.jpg
---------------------------
sid 2130
vfilename 2009062615063867492
url http://lz.dhot.v.iask.com/f/1/0ee2ae8b973988f6a93c071c8045ca5217266409.mp4
status 0
filename 2009062615063867492-00.mp4
imgfile 2009062615063825434.jpg
vid 93
imgurl http://cache.mars.sina.com.cn/nd/movievideo//thumb/2/1502_120160.jpg
---------------------------
sid 2131
vfilename 2009062615064184076
url http://lz5.dhot.v.iask.com/f/1/36d3dadacb8d6bda434a58e7418ad3cc19037464.flv
status 0
filename 2009062615064184076-00.flv
imgfile 2009062615064136733.jpg
vid 94
imgurl http://cache.mars.sina.com.cn/nd/movievideo//thumb/6/2106_120160.jpg
sid 1
vfilename 200905252009235799
url http://d18.v.iask.com/f/1/f47817a394730dc682e660b943e84cc41006606.flv
status 0
filename 200905252009235799-00.flv
imgfile 200905252009234399.jpg
vid 1
imgurl http://p4.v.iask.com/95/595/1757503_1.jpg
---------------------------
sid 2130
vfilename 2009062615063867492
url http://lz.dhot.v.iask.com/f/1/0ee2ae8b973988f6a93c071c8045ca5217266409.mp4
status 0
filename 2009062615063867492-00.mp4
imgfile 2009062615063825434.jpg
vid 93
imgurl http://cache.mars.sina.com.cn/nd/movievideo//thumb/2/1502_120160.jpg
---------------------------
sid 2131
vfilename 2009062615064184076
url http://lz5.dhot.v.iask.com/f/1/36d3dadacb8d6bda434a58e7418ad3cc19037464.flv
status 0
filename 2009062615064184076-00.flv
imgfile 2009062615064136733.jpg
vid 94
imgurl http://cache.mars.sina.com.cn/nd/movievideo//thumb/6/2106_120160.jpg
