springboot模糊查詢

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}%’)會變為(‘%?%’),而(‘%?%’)會被看作是一個字符串，所以Java代碼在執行找不到用於匹配參數的 ‘?’ ,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
　　這個方法沒試過，就不貼代碼和結果了。