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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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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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