MyBatis实现模糊查询的几种方式

2019-11-26 09:42:49

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在学习MyBatis过程中想实现模糊查询，可惜失败了。后来上百度上查了一下，算是解决了。记录一下MyBatis实现模糊查询的几种方式。

数据库表名为test_student,初始化了几条记录，如图：

起初我在MyBatis的mapper文件中是这样写的：

 <select id="searchStudents" resultType="com.example.entity.StudentEntity"  parameterType="com.example.entity.StudentEntity">  SELECT * FROM test_student  <where>   <if test="age != null and age != '' and compare != null and compare != ''">    age    ${compare}    #{age}   </if>   <if test="name != null and name != ''">    AND name LIKE '%#{name}%'   </if>   <if test="address != null and address != ''">    AND address LIKE '%#{address}%'   </if>  </where>  ORDER BY id </select>

写完后自我感觉良好，很开心的就去跑程序了，结果当然是报错了：

经百度得知，这么写经MyBatis转换后(‘%#{name}%')会变为(‘%?%'),而(‘%?%')会被看作是一个字符串，所以Java代码在执行找不到用于匹配参数的 ‘?' ,然后就报错了。

解决方法

1.用${…}代替#{…}

<select id="searchStudents" resultType="com.example.entity.StudentEntity"  parameterType="com.example.entity.StudentEntity">  SELECT * FROM test_student  <where>   <if test="age != null and age != '' and compare != null and compare != ''">    age    ${compare}    #{age}   </if>   <if test="name != null and name != ''">    AND name LIKE '%${name}%'   </if>   <if test="address != null and address != ''">    AND address LIKE '%${address}%'   </if>  </where>  ORDER BY id </select>

查询结果如下图：

注：使用${…}不能有效防止SQL注入，所以这种方式虽然简单但是不推荐使用！！！

2.把'%#{name}%'改为”%”#{name}”%”

 <select id="searchStudents" resultType="com.example.entity.StudentEntity"  parameterType="com.example.entity.StudentEntity">  SELECT * FROM test_student  <where>   <if test="age != null and age != '' and compare != null and compare != ''">    age    ${compare}    #{age}   </if>   <if test="name != null and name != ''">    AND name LIKE "%"#{name}"%"   </if>   <if test="address != null and address != ''">    AND address LIKE "%"#{address}"%"   </if>  </where>  ORDER BY id </select>

查询结果：

3.使用sql中的字符串拼接函数

<select id="searchStudents" resultType="com.example.entity.StudentEntity"  parameterType="com.example.entity.StudentEntity">  SELECT * FROM test_student  <where>   <if test="age != null and age != '' and compare != null and compare != ''">    age    ${compare}    #{age}   </if>   <if test="name != null and name != ''">    AND name LIKE CONCAT(CONCAT('%',#{name},'%'))   </if>   <if test="address != null and address != ''">    AND address LIKE CONCAT(CONCAT('%',#{address},'%'))   </if>  </where>  ORDER BY id </select>

查询结果：

4.使用标签

<select id="searchStudents" resultType="com.example.entity.StudentEntity"  parameterType="com.example.entity.StudentEntity">  <bind name="pattern1" value="'%' + _parameter.name + '%'" />  <bind name="pattern2" value="'%' + _parameter.address + '%'" />  SELECT * FROM test_student  <where>   <if test="age != null and age != '' and compare != null and compare != ''">    age    ${compare}    #{age}   </if>   <if test="name != null and name != ''">    AND name LIKE #{pattern1}   </if>   <if test="address != null and address != ''">    AND address LIKE #{pattern2}   </if>  </where>  ORDER BY id </select>

查询结果：

5.在Java代码中拼接字符串

public static void main(String[] args) {  try {   int count = 500;   long begin = System.currentTimeMillis();   testString(count);   long end = System.currentTimeMillis();   long time = end - begin;   System.out.println("String 方法拼接"+count+"次消耗时间：" + time + "毫秒");   begin = System.currentTimeMillis();   testStringBuilder(count);   end = System.currentTimeMillis();   time = end - begin;   System.out.println("StringBuilder 方法拼接"+count+"次消耗时间：" + time + "毫秒");  } catch (Exception e) {   e.printStackTrace();  } } private static String testString(int count) {  String result = "";  for (int i = 0; i < count; i++) {   result += "hello ";  }  return result; } private static String testStringBuilder(int count) {  StringBuilder sb = new StringBuilder();  for (int i = 0; i < count; i++) {   sb.append("hello");  }  return sb.toString(); }

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