MyBatis實現模糊查詢的幾種方式

更新時間：2018年08月22日 11:07:11 作者：行癲

這篇文章主要介紹了MyBatis實現模糊查詢的幾種方式，小編覺得挺不錯的，現在分享給大家，也給大家做個參考。一起跟隨小編過來看看吧

在學習MyBatis過程中想實現模糊查詢，可惜失敗了。后來上百度上查了一下，算是解決了。記錄一下MyBatis實現模糊查詢的幾種方式。

數據庫表名為test_student,初始化了幾條記錄，如圖：

起初我在MyBatis的mapper文件中是這樣寫的：

 <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>

寫完后自我感覺良好，很開心的就去跑程序了，結果當然是報錯了：

經百度得知，這么寫經MyBatis轉換后(‘%#{name}%')會變?yōu)?‘%?%'),而(‘%?%')會被看作是一個字符串，所以Java代碼在執(zhí)行找不到用于匹配參數的 ‘?' ,然后就報錯了。

解決方法

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>

查詢結果如下圖：

注：使用${…}不能有效防止SQL注入，所以這種方式雖然簡單但是不推薦使用?。?！

2.把'%#{name}%'改為”%”#{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>

查詢結果：

3.使用sql中的字符串拼接函數

<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>

查詢結果：

4.使用標簽

<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>

查詢結果：

5.在Java代碼中拼接字符串

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+"次消耗時間：" + time + "毫秒");

   begin = System.currentTimeMillis();
   testStringBuilder(count);
   end = System.currentTimeMillis();
   time = end - begin;
   System.out.println("StringBuilder 方法拼接"+count+"次消耗時間：" + 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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