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（六）并发处理
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二、异常日志
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五、MySQL数据库
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（三）SQL语句
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六、工程结构
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（一）应用分层
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（三）服务器
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附1：版本历史
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附2：本手册专有名词
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<!-- Title -->
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<h1>
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<i class="fa fa-circle-o-notch fa-spin"></i>
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<a href=".." >（四）ORM映射</a>
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</h1>
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</div>
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<h2 id="四-orm映射">(四) ORM映射</h2>
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<ol>
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<li>【强制】在表查询中，一律不要使用 * 作为查询的字段列表，需要哪些字段必须明确写明。
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<br><span style="color:orange">说明</span>：1）增加查询分析器解析成本。2）增减字段容易与resultMap配置不一致。 </li>
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<li>【强制】POJO类的布尔属性不能加is，而数据库字段必须加is_，要求在resultMap中进行字段与属性之间的映射。
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<br><span style="color:orange">说明</span>：参见定义POJO类以及数据库字段定义规定，在<resultmap>中增加映射，是必须的。在MyBatis Generator生成的代码中，需要进行对应的修改。</resultmap></li>
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<li>【强制】不要用resultClass当返回参数，即使所有类属性名与数据库字段一一对应，也需要定义；反过来，每一个表也必然有一个与之对应。
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<br><span style="color:orange">说明</span>：配置映射关系，使字段与DO类解耦，方便维护。 </li>
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<li>【强制】sql.xml配置参数使用：#{}，#param# 不要使用${} 此种方式容易出现SQL注入。 </li>
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<li><p>【强制】iBATIS自带的queryForList(String statementName,int start,int size)不推荐使用。
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<br><span style="color:orange">说明</span>：其实现方式是在数据库取到statementName对应的SQL语句的所有记录，再通过subList取start,size的子集合。
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<br><span style="color:green">正例</span>：</p>
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<pre class="language-"><code> Map<span class="token tag"><span class="token tag"><span class="token punctuation"><</span>String,</span> <span class="token attr-name">Object</span><span class="token punctuation">></span></span> map = new HashMap<span class="token tag"><span class="token tag"><span class="token punctuation"><</span>String,</span> <span class="token attr-name">Object</span><span class="token punctuation">></span></span>();
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map.put("start", start);
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map.put("size", size);
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</code></pre></li>
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<li><p>【强制】不允许直接拿HashMap与Hashtable作为查询结果集的输出。
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<br><span style="color:orange">说明</span>：resultClass=”Hashtable”，会置入字段名和属性值，但是值的类型不可控。</p>
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</li>
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<li>【强制】更新数据表记录时，必须同时更新记录对应的gmt_modified字段值为当前时间。</li>
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<li>【推荐】不要写一个大而全的数据更新接口。传入为POJO类，不管是不是自己的目标更新字段，都进行update table set c1=value1,c2=value2,c3=value3; 这是不对的。执行SQL时，不要更新无改动的字段，一是易出错；二是效率低；三是增加binlog存储。 </li>
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<li>【参考】<code>@Transactional</code>事务不要滥用。事务会影响数据库的QPS，另外使用事务的地方需要考虑各方面的回滚方案，包括缓存回滚、搜索引擎回滚、消息补偿、统计修正等。 </li>
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<li>【参考】<code><span class="token tag"><span class="token tag"><span class="token punctuation"><</span>isEqual</span><span class="token punctuation">></span></span></code>中的compareValue是与属性值对比的常量，一般是数字，表示相等时带上此条件；<code><span class="token tag"><span class="token tag"><span class="token punctuation"><</span>isNotEmpty</span><span class="token punctuation">></span></span></code>表示不为空且不为null时执行；<code><span class="token tag"><span class="token tag"><span class="token punctuation"><</span>isNotNull</span><span class="token punctuation">></span></span></code>表示不为null值时执行。 </li>
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