06.動態SQL和foreach

動態sql:

映射文件代碼:

 <!-- 動態sql,根據名字和年齡查詢,where標簽會處理第一個and，其他位置的and不會自動處理 -->
  <select id="queryStudentByNameAndAge" parameterType="student" resultMap="student1">
    select * from student 
    <!-- 1.使用where 1=1 ，避免where后直接跟and -->
     <!-- 2.使用where關鍵字，避免where后直接跟and -->
    <where>
        <if test="sname != null and sname != '' ">
            and sname = #{sname}
        </if>
        <if test="age != null and age != '' ">
            and age = #{age}
        </if>
    </where>
  </select>

foreach循環屬性集合:

映射文件:

  <!-- foreach循環屬性集合-->
  <select id="queryStudentsByHomeAddress" parameterType="Home" resultMap="student1">
    select * from student 
    <where>
    <if test="homeAddress != null and homeAddress != '' ">
    <!-- colleaction是屬性中的集合，item是遍歷出來的每個元素，open是循環結果前邊的東西，close是循環結果后邊要加的東西，separator是循環結果用什么符號分隔 -->
        <foreach collection="homeAddress" item="homeAr" open=" and homeaddress in (" close=" )" separator=",">
            #{homeAr}            
        </foreach>
    </if>    
    </where>
  </select>

測試類:

 Home home = new Home();
 List<String> homeAddress = new ArrayList<String>();
 homeAddress.add("北京");
 homeAddress.add("南京");
 home.setHomeAddress(homeAddress);
 List<Student> stu = studentMapper.queryStudentsByHomeAddress(home);

foreach循環集合:

映射文件:（需要注意的是循環要循環list）

 <!-- foreach循環集合-->
  <select id="queryStudentsWithList" parameterType="list" resultMap="student1">
    select * from student 
    <where>
    <!-- 必須寫list -->
    <if test="list != null and list != '' ">
        <foreach collection="list" item="homeAr" open=" and homeaddress in (" close=" )" separator=",">
            #{homeAr}            
        </foreach>
    </if>    
    </where>
  </select>

測試類:

List<String> list = new ArrayList<String>();
list.add("北京");
list.add("南京");
List<Student> stu = studentMapper.queryStudentsWithList(list);

foreach循環數組:

映射文件:(注意循環必須都寫array，輸入參數不是簡單類型時都寫Object[])

 <!-- foreach循環數組-->
  <select id="queryStudentsWithArray" parameterType="Object[]" resultMap="student1">
    select * from student 
    <where>
    <!-- 必須寫array -->
    <if test="array != null and array != '' ">
        <foreach collection="array" item="homeAr" open=" and homeaddress in (" close=" )" separator=",">
            #{homeAr}            
        </foreach>
    </if>    
    </where>
  </select>

測試類:

String[] str = {"北京","南京"};
List<Student> stu = studentMapper.queryStudentsWithArray(str);

foreach循環對象數組:

映射文件:(需要注意的是這時的item要寫循環出來的對象了，不能瞎寫名字了,然后通過對象點的方式獲取值)

<!-- foreach循環對象數組-->
  <select id="queryStudentsWithObjectArray" parameterType="Object[]" resultMap="student1">
    select * from student 
    <where>
    <!-- 必須寫array -->
    <if test="array != null and array != '' ">
     <!-- item里邊寫的是循環出來的對象 -->
        <foreach collection="array" item="address" open=" and homeaddress in (" close=" )" separator=",">
            <!-- 對象點屬性獲取值 -->
            #{address.homeAddress}            
        </foreach>
    </if>    
    </where>
  </select>

測試類:

Address addr1 = new Address();
addr1.setHomeAddress("北京");
Address addr2 = new Address();
addr2.setHomeAddress("南京");
Address[] address = {addr1,addr2};
List<Student> s = studentMapper.queryStudentsWithObjectArray(address);