MyBatis实现模糊查询的几种方式

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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