06.動態SQL和foreach

動態sql:

映射文件代碼:

 1  <!-- 動態sql,根據名字和年齡查詢,where標籤會處理第一個and，其餘位置的and不會自動處理 -->
 2   <select id="queryStudentByNameAndAge" parameterType="student" resultMap="student1">
 3     select * from student 
 4     <!-- 1.使用where 1=1 ，避免where後直接跟and -->
 5      <!-- 2.使用where關鍵字，避免where後直接跟and -->
 6     <where>
 7         <if test="sname != null and sname != '' ">
 8             and sname = #{sname}
 9         </if>
10         <if test="age != null and age != '' ">
11             and age = #{age}
12         </if>
13     </where>
14   </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是遍歷出來的每一個元素，open是循環結果前邊的東西，close是循環結果後邊要加的東西，separator是循環結果用什麼符號分隔 -->
        <foreach collection="homeAddress" item="homeAr" open=" and homeaddress in (" close=" )" separator=",">
            #{homeAr}            
        </foreach>
    </if>    
    </where>
  </select>

測試類:

1  Home home = new Home();
2  List<String> homeAddress = new ArrayList<String>();
3  homeAddress.add("北京");
4  homeAddress.add("南京");
5  home.setHomeAddress(homeAddress);
6  List<Student> stu = studentMapper.queryStudentsByHomeAddress(home);

foreach循環集合:

映射文件:（須要注意的是循環要循環list）

 1  <!-- foreach循環集合-->
 2   <select id="queryStudentsWithList" parameterType="list" resultMap="student1">
 3     select * from student 
 4     <where>
 5     <!-- 必須寫list -->
 6     <if test="list != null and list != '' ">
 7         <foreach collection="list" item="homeAr" open=" and homeaddress in (" close=" )" separator=",">
 8             #{homeAr}            
 9         </foreach>
10     </if>    
11     </where>
12   </select>

測試類:

1 List<String> list = new ArrayList<String>();
2 list.add("北京");
3 list.add("南京");
4 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[])

 1  <!-- foreach循環數組-->
 2   <select id="queryStudentsWithArray" parameterType="Object[]" resultMap="student1">
 3     select * from student 
 4     <where>
 5     <!-- 必須寫array -->
 6     <if test="array != null and array != '' ">
 7         <foreach collection="array" item="homeAr" open=" and homeaddress in (" close=" )" separator=",">
 8             #{homeAr}            
 9         </foreach>
10     </if>    
11     </where>
12   </select>

測試類:

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

foreach循環對象數組:

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

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

測試類:

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