为什么Mybatis可以通过SO加入查询条件

1、比如我们在SignInfoMapper.xml中，

     <sql id= "SO_Where_Clause">

             <where>

                  1=1

                   <if test="@org.apache.commons.lang.StringUtils@isNotBlank(province)" >

                        and t.PROVINCE=#{province}

                   </if>

                   <if test="@org.apache.commons.lang.StringUtils@isNotBlank(city)" >

                        and t.CITY=#{city}

                   </if>

                   <if test="@org.apache.commons.lang.StringUtils@isNotBlank(county)" >

                        and t.COUNTY=#{county}

                   </if>

                   <if test="isSearched != -1" >

                        and NVL(t.IS_SEARCHED,0) = #{isSearched}

                   </if>

                   <if test="reqTimeFrom!=null" >

                      and t.REQ_TIME <![CDATA[ >= ]]> #{reqTimeFrom}

                   </if>

                   <if test="reqTimeTo!=null" >

                      and t.REQ_TIME <![CDATA[ <= ]]> #{reqTimeTo}+1

                   </if>

             </where>

             <include refid="sqlmap.common.Order_By_Clause" />

       </sql>

    然后<select id= "getListBySo" resultMap ="signInfoVoResultMap">

            SELECT t.* FROM ASS_SIGN_INFO t

             <include refid="SO_Where_Clause" />

       </select>

    然后：

      @Override

public <E> List<E> getVOListBySo(BasePageSO so) {

    RowBounds rowBounds = new RowBounds((so.getPageNumber() - 1) *so.getObjectsPerPage(), so.getObjectsPerPage());

     return sqlSessionTemplate.selectList(getStatementPrefix() + POSTFIX_GET_LIST_BY_SO, so, rowBounds);

    }

    这样就可以实现动态的查询了呢?Mybatis是如何将这个动态的参数拼接到SQL上的呢？

2、我们通过调试查看该方法的执行过程，如下所示：

    2.1、

     @Test

    public void testGetPageList() {

        ReqLogSO sos = new ReqLogSO();

        sos.setCity( "上海市");

        sos.setProvince( "上海");

        List<ReqLogVO> list = reqLogService.getVOListBySo(sos);

        assertTrue(list.size() > 0);

    }

    2.2、reqLogService .getVOListBySo(sos);调用：

   

@Override

public <E> List<E> getVOListBySo(BasePageSO so) {

        RowBounds rowBounds =

new RowBounds((so.getPageNumber() - 1) *so.getObjectsPerPage(), so.getObjectsPerPage());

       

return sqlSessionTemplate.selectList(getStatementPrefix() + POSTFIX_GET_LIST_BY_SO, so, rowBounds);

    }

    2.3、上述下划线的方法调用，SqlSessionTemplate.class中的：

public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {  

return this.sqlSessionProxy .<E> selectList(statement, parameter, rowBounds);}

2.4、接着调用DefaultSqlSession.class中的：

public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {

try {

      MappedStatement ms =configuration.getMappedStatement(statement);

      List<E> result =

executor.<E>query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER );

     

return result;

    }

catch (Exception e) {

    ...

  }

2.5、executor.<E>query()方法接着调用CachingExecutor的方法：

public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {

    BoundSql boundSql = ms.getBoundSql(parameterObject);

    CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);

    return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);

  }