Mybatis之动态sql

Mybatis之动态sql

数据表

 <!--创建表 -->
CREATE TABLE `books` (`bid` INT AUTO_INCREMENT NOT NULL COMMENT '编号',
  `title` VARCHAR (50) NOT NULL COMMENT '书名',
  `author` VARCHAR (30) NOT NULL COMMENT '作者',
  `language` VARCHAR (20) NOT NULL COMMENT '语言',
  `dateOfPublish` DATE NOT NULL COMMENT '出版日期',
  `publisher` VARCHAR (50) NOT NULL COMMENT '出版社',
  `type` VARCHAR (30) NOT NULL COMMENT '类型',
  PRIMARY KEY (`bid`)
 )ENGINE = INNODB DEFAULT CHARSET = utf8; 
 
 
<!--插入数据 -->
INSERT INTO `books` (`title`,`author`,`language`,`dateOfPublish`,`publisher`,`type`) VALUES
("人间失格","太宰治","日文",DATE"1948-4-8","浙江文艺出版社","小说"),
("罗生门","芥川龙之介","中文",DATE"1997-10-1","湖南文艺出版社","小说"),
("茶花女","小仲马","中文",DATE"1997-3-1","外国文学出版社","小说"),
("霍乱时期的爱情","加西亚·马尔克斯","中文",DATE"1985-10-1","外国文学出版社","小说");

pojo类

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Books {
    private int bid;
    private String title;
    private String author;
    private String language;
    private Date dateOfPublish;
    private String publisher;
    private String type;
}

1：if

标签：满足if条件，则拼接if标签中的语句

<!--BooksDao接口的方法-->
public ArrayList<Books> getBooks(HashMap<String,String> map);
    
<!--BooksDaoMapper.xml-->
	<select id="getBooks"  parameterType="map" resultType="book">
        select * from books
        where 1 = 1
        <if test="title != null">
            and title  = #{title}
        </if>
        <if test="author != null">
            and author = #{author}
        </if>
        <if test="language != null">
            and language = #{language}
        </if>
        <if test="dateOfPath != null">
            and dateOfPath = #{dateOfPath}
        </if>
        <if test="publisher != null">
            and publisher = #{publisher}
        </if>
        <if test="type != null">
            and type = #{type}
        </if>
    </select>    

测试：

  @Test
    public void query() {
        SqlSession sqlSession = DbUtils.getSqlSession();
        BooksDao booksDao = sqlSession.getMapper(BooksDao.class);

        Date date = new Date();
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");

        HashMap<String, String> hashMap = new HashMap<String, String>();


        hashMap.put("language","中文");
        hashMap.put("author","芥川龙之介");
        ArrayList<Books> list = booksDao.getBooks(hashMap);
        for (Books book : list) {

            System.out.println(book);

        }

结果：

[com.cugb.dao.BooksDao.getBooks]-==> Preparing: select * from books where 1 = 1 and author = ? and language = ? 
[com.cugb.dao.BooksDao.getBooks]-==> Parameters: 芥川龙之介(String), 中文(String)
[com.cugb.dao.BooksDao.getBooks]-<==      Total: 1
Books(bid=2, title=罗生门, author=芥川龙之介, language=中文, dateOfPublish=Wed Oct 01 00:00:00 CST 1997, publisher=湖南文艺出版社, type=dang小说)

当if标签中的test属性为true时,sql拼接标签内的语句，否则不拼接

2：where、 choose、 when、otherwise

这是一对组合的用法，相当于java中的switch case

<!--BooksDao接口的方法-->
public ArrayList<Books> getBooks2(HashMap<String,String> map);
 <select id="getBooks2"  parameterType="map" resultType="book">
        select * from books
        <where>
            <choose>

                <when test="title != null">
                    and title  = #{title}
                </when>

                <when test="author != null">
                    and author = #{author}
                </when>

                <when test="language != null">
                    and language = #{language}
                </when>

                <when test="dateOfPublish != null">
                    and dateOfPublish = #{dateOfPublish}
                </when>

                <when test="publisher != null">
                    and publisher = #{publisher}
                </when>

                <when test="type != null">
                    and type = #{type}
                </when>
                <otherwise>
                    
                </otherwise>

            </choose>
        </where>
    </select>

当when的test属性为true时，跳出choose，若都为false则执行otherwise，where则是去除拼接语句第一个and

测试

   @Test
    public void query() {
        SqlSession sqlSession = DbUtils.getSqlSession();
        BooksDao booksDao = sqlSession.getMapper(BooksDao.class);

        Date date = new Date();
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");

        HashMap<String, String> hashMap = new HashMap<String, String>();


        hashMap.put("language","中文");
        hashMap.put("author","芥川龙之介");
        ArrayList<Books> list = booksDao.getBooks2(hashMap);
        for (Books book : list) {

            System.out.println(book);

        }

结果：

[com.cugb.dao.BooksDao.getBooks2]-==>  Preparing: select * from books WHERE author = ? 
[com.cugb.dao.BooksDao.getBooks2]-==> Parameters: 芥川龙之介(String)
[com.cugb.dao.BooksDao.getBooks2]-<==      Total: 1
Books(bid=2, title=罗生门, author=芥川龙之介, language=中文, dateOfPublish=Wed Oct 01 00:00:00 CST 1997, publisher=湖南文艺出版社, type=小说)

这时候你发现，sql语句跟之前的边了，它只有一个条件，是因为when中的test只要有一个是true，就会跳出true。and也被where标签给去除了。

** 3：set**

if标签中的test属性为true时，拼接标签中的sql语句，并去除最后的，

<update id="upateBook" parameterType="map" >
        update books
        <set>
            <if test="title != null">
                title = #{title},
            </if>
            <if test="author != null">
                author = #{author},
            </if> 
             <if test="language != null">
                 language = #{language},
             </if>
             <if test="dateOfPublish">
                 dateOfPublish = #{dateOfPublish},
             </if>
             <if test="type">
                 type = #{type},
             </if>
        </set>
    where
    bid = 3
</update>

测试：

    @Test
    public void update(){
        SqlSession sqlSession = DbUtils.getSqlSession();
        BooksDao booksDao = sqlSession.getMapper(BooksDao.class);

        HashMap<String, String> hashMap = new HashMap<String, String>();
        
        //第一次查询
        ArrayList<Books> list = booksDao.getBooks2(hashMap);
        for (Books book : list) {

            System.out.println(book);
        }


        hashMap.put("language","英文");

        booksDao.upateBook(hashMap);
        
        //清楚map的数据，并进行二次查询
        hashMap.clear();
        list = booksDao.getBooks2(hashMap);
        for (Books book : list) {

            System.out.println(book);
        }

    }

结果:

[com.cugb.dao.BooksDao.getBooks2]-==>  Preparing: select * from books 
[com.cugb.dao.BooksDao.getBooks2]-==> Parameters: 
[com.cugb.dao.BooksDao.getBooks2]-<==      Total: 4
Books(bid=1, title=人间失格, author=太宰治, language=日文, dateOfPublish=Thu Apr 08 00:00:00 CST 1948, publisher=浙江文艺出版社, type=小说)
Books(bid=2, title=罗生门, author=芥川龙之介, language=中文, dateOfPublish=Wed Oct 01 00:00:00 CST 1997, publisher=湖南文艺出版社, type=小说)
Books(bid=3, title=茶花女, author=小仲马, language=中文, dateOfPublish=Sat Mar 01 00:00:00 CST 1997, publisher=外国文学出版社, type=小说)
Books(bid=4, title=霍乱时期的爱情, author=加西亚·马尔克斯, language=中文, dateOfPublish=Tue Oct 01 00:00:00 CST 1985, publisher=外国文学出版社, type=小说)
[com.cugb.dao.BooksDao.upateBook]-==>  Preparing: update books SET language = ? where bid = 3; 
[com.cugb.dao.BooksDao.upateBook]-==> Parameters: 英文(String)
[com.cugb.dao.BooksDao.upateBook]-<==    Updates: 1
[com.cugb.dao.BooksDao.getBooks2]-==>  Preparing: select * from books 
[com.cugb.dao.BooksDao.getBooks2]-==> Parameters: 
[com.cugb.dao.BooksDao.getBooks2]-<==      Total: 4
Books(bid=1, title=人间失格, author=太宰治, language=日文, dateOfPublish=Thu Apr 08 00:00:00 CST 1948, publisher=浙江文艺出版社, type=小说)
Books(bid=2, title=罗生门, author=芥川龙之介, language=中文, dateOfPublish=Wed Oct 01 00:00:00 CST 1997, publisher=湖南文艺出版社, type=小说)
Books(bid=3, title=茶花女, author=小仲马, language=英文, dateOfPublish=Sat Mar 01 00:00:00 CST 1997, publisher=外国文学出版社, type=小说)
Books(bid=4, title=霍乱时期的爱情, author=加西亚·马尔克斯, language=中文, dateOfPublish=Tue Oct 01 00:00:00 CST 1985, publisher=外国文学出版社, type=小说)

两次查询结果，发现《茶花女》的language变成了英文,set语句起了作用。

4：trim

trim是用来where 和set 去除拼接语句指定位置的字符,trim中有4个标签

prefix:给sql拼接语句添加前缀

suffix:给sql拼接语句添加后缀

prefixOverrides :去除sql拼接语句前的指定的关键字

suffixOverrides :去除sql拼接语句后的指定的关键字

用trim代替where、when、choose

  /*
  查询书籍
   */
  public ArrayList<Books> getBooks3(HashMap<String,String> map);
      

	<select id="getBooks3" parameterType="map" resultType="book">
        select * from books
        <trim prefix="where" prefixOverrides="and|or">
            <if test="title != null">
                and title  = #{title}
            </if>
            <if test="author != null">
                and author = #{author}
            </if>
            <if test="language != null">
                and language = #{language}
            </if>
            <if test="dateOfPath != null">
                and dateOfPath = #{dateOfPath}
            </if>
            <if test="publisher != null">
                and publisher = #{publisher}
            </if>
            <if test="type != null">
                and type = #{type}
            </if>
        </trim>
    </select>

测试

    @Test
    public void query() {
        SqlSession sqlSession = DbUtils.getSqlSession();
        BooksDao booksDao = sqlSession.getMapper(BooksDao.class);

        HashMap<String, String> hashMap = new HashMap<String, String>();

        hashMap.put("language","中文");
        hashMap.put("author","芥川龙之介");
        ArrayList<Books> list = booksDao.getBooks3(hashMap);
        for (Books book : list) {

            System.out.println(book);
        }

    }

测试结果

[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Opening JDBC Connection
[org.apache.ibatis.datasource.pooled.PooledDataSource]-Created connection 1800659519.
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@6b53e23f]
[com.cugb.dao.BooksDao.getBooks3]-==>  Preparing: select * from books where author = ? and language = ? 
[com.cugb.dao.BooksDao.getBooks3]-==> Parameters: 芥川龙之介(String), 中文(String)
[com.cugb.dao.BooksDao.getBooks3]-<==      Total: 1
Books(bid=2, title=罗生门, author=芥川龙之介, language=中文, dateOfPublish=Wed Oct 01 00:00:00 CST 1997, publisher=湖南文艺出版社, type=小说)

执行的sql语句

reparing: select * from books where author = ? and language = ? 
[com.cugb.dao.BooksDao.getBooks3]-==> Parameters: 芥川龙之介(String), 中文(String)
[com.cugb.dao.BooksDao.getBooks3]-<==      Total: 1

从结果来看，trim实现了where、when、choose组合的效果

用trim代替set

	 /*
   修改书籍信息
    */
    public int upateBook2(HashMap<String,String> map);

        
    <update id="upateBook2" parameterType="map" >
        update books
        <trim prefix="set" suffixOverrides=",">
            <if test="title != null">
                title = #{title},
            </if>
            <if test="author != null">
                author = #{author},
            </if>
            <if test="language != null">
                language = #{language},
            </if>
            <if test="dateOfPublish">
                dateOfPublish = #{dateOfPublish},
            </if>
            <if test="type">
                type = #{type},
            </if>
        </trim>

        where
        bid = 3;
    </update>     

测试

 @Test
    public void update(){
        SqlSession sqlSession = DbUtils.getSqlSession();
        BooksDao booksDao = sqlSession.getMapper(BooksDao.class);

        HashMap<String, String> hashMap = new HashMap<String, String>();

        //第一次查询
        ArrayList<Books> list = booksDao.getBooks2(hashMap);
        for (Books book : list) {

            System.out.println(book);
        }


        hashMap.put("language","英文");
		//修改bid=3的语言
        booksDao.upateBook2(hashMap);

        //清除map的数据，并进行二次查询
        hashMap.clear();
        list = booksDao.getBooks2(hashMap);
        for (Books book : list) {

            System.out.println(book);
        }

    }

结果

[com.cugb.dao.BooksDao.getBooks2]-==>  Preparing: select * from books 
[com.cugb.dao.BooksDao.getBooks2]-==> Parameters: 
[com.cugb.dao.BooksDao.getBooks2]-<==      Total: 4
Books(bid=1, title=人间失格, author=太宰治, language=日文, dateOfPublish=Thu Apr 08 00:00:00 CST 1948, publisher=浙江文艺出版社, type=小说)
Books(bid=2, title=罗生门, author=芥川龙之介, language=中文, dateOfPublish=Wed Oct 01 00:00:00 CST 1997, publisher=湖南文艺出版社, type=小说)
Books(bid=3, title=茶花女, author=小仲马, language=中文, dateOfPublish=Sat Mar 01 00:00:00 CST 1997, publisher=外国文学出版社, type=小说)
Books(bid=4, title=霍乱时期的爱情, author=加西亚·马尔克斯, language=中文, dateOfPublish=Tue Oct 01 00:00:00 CST 1985, publisher=外国文学出版社, type=小说)
[com.cugb.dao.BooksDao.upateBook2]-==>  Preparing: update books set language = ? where bid = 3; 
[com.cugb.dao.BooksDao.upateBook2]-==> Parameters: 英文(String)
[com.cugb.dao.BooksDao.upateBook2]-<==    Updates: 1
[com.cugb.dao.BooksDao.getBooks2]-==>  Preparing: select * from books 
[com.cugb.dao.BooksDao.getBooks2]-==> Parameters: 
[com.cugb.dao.BooksDao.getBooks2]-<==      Total: 4
Books(bid=1, title=人间失格, author=太宰治, language=日文, dateOfPublish=Thu Apr 08 00:00:00 CST 1948, publisher=浙江文艺出版社, type=小说)
Books(bid=2, title=罗生门, author=芥川龙之介, language=中文, dateOfPublish=Wed Oct 01 00:00:00 CST 1997, publisher=湖南文艺出版社, type=小说)
Books(bid=3, title=茶花女, author=小仲马, language=英文, dateOfPublish=Sat Mar 01 00:00:00 CST 1997, publisher=外国文学出版社, type=小说)
Books(bid=4, title=霍乱时期的爱情, author=加西亚·马尔克斯, language=中文, dateOfPublish=Tue Oct 01 00:00:00 CST 1985, publisher=外国文学出版社, type=小说)

第一次查询

Books(bid=3, title=茶花女, author=小仲马, language=中文, dateOfPublish=Sat Mar 01 00:00:00 CST 1997, publisher=外国文学出版社, type=小说)

第二次查询

Books(bid=3, title=茶花女, author=小仲马, language=英文, dateOfPublish=Sat Mar 01 00:00:00 CST 1997, publisher=外国文学出版社, type=小说)

结果确实改变了language.

所以trim可以实现where when choose 和set 的功能。