MyBatis實現模糊查詢的幾種方式

 

　　在學習MyBatis過程當中想實現模糊查詢，惋惜失敗了。後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。
　　數據庫表名爲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>

寫完後自我感受良好，很開心的就去跑程序了，結果固然是報錯了：

　　經百度得知，這麼寫經MyBatis轉換後(‘%#{name}%’)會變爲(‘%?%’),而(‘%?%’)會被看做是一個字符串，因此Java代碼在執行找不到用於匹配參數的 ‘?’ ,而後就報錯了。

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>

查詢結果以下圖：

　　注：使用${…}不能有效防止SQL注入，因此這種方式雖然簡單可是不推薦使用！！！

2.把’%#{name}%’改成」%」#{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.使用標籤

<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。

————2017.07.03