Mybatis fuzzy query, paging and alias configuration

mybatis fuzzy query (3 types)

The first

select * from user where username like "%" #{name} "%"

The second

select * from user where username like "%${value}%"

The third

<!--concat拼接字符串  mysql独有的函数-->
select * from user where username like  concat("%",#{username},"%")

The whole network says this, but I don’t know how to implement injection.

• #{} is pre-compilation processing, ${} is string replacement. When Mybatis processes #{}, it replaces #{} in sql with a? Sign, and calls the set method of PreparedStatement to assign;

• When Mybatis processes ${}, it replaces ${} with the value of the variable.

• Using #{} can effectively prevent SQL injection and improve system security.

Configure aliases (typeAliases)

The first way : add in the mybatis-config.xml core configuration file <configuration></configuration>:

   <typeAlias type="com.lu.pojo.User" alias="User"/>

User can be used wherever com.lu.pojo.User is used.

The second way:
You can also specify a package name, MyBatis will search for the required Java Bean under the package name, for example:

<typeAliases>
  <package name="com.lu.pojo"/>
</typeAliases>

In the absence of annotations, the unqualified class name of Bean's first letter and lowercase will be used as its alias. For example, the alias of com.lu.pojo.User is user; if there is an annotation, the alias is the annotation value. such as:

@Alias("user")
public class User{
    
    
    ...
}

Inconsistent property name and field name

Question: The password in the database is represented by pwd, and the password is represented by the entity class. The query result will be null.

The first way : alias with as in sql statement.

    <select id="getUserById"  resultType="com.lu.pojo.User">
        select id,username, pwd as password from user where id = #{id}
    </select>

The second way: use resultMap for mapping.

    <!--结果集映射-->
    <resultMap id="userMap" type="com.lu.pojo.User">
        <!--property是实体类中的属性，column是数据库中的字段 -->
        <result property="password" column="pwd" />
    </resultMap>

    <select id="getUserById"  resultMap="userMap">
        select id,username, pwd from user where id = #{id}
    </select>

3 ways of paging query

1. Paging through limit

mapper interface:

    //使用limit实现分页
    List<User> getUserByLimit(Map<String,Integer> map);

In Mapper.xml:

    <select id="getUserByLimit" parameterType="map" resultType="com.lu.pojo.User">
        select * from user limit #{offset}, #{pageSize}
    </select>

testing method:

    @Test
    public void getUserByLimit(){
    
    
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        Map<String, Integer> map = new HashMap<String, Integer>();
        map.put("offset",1);
        map.put("pageSize",2);
        List<User> users =  userMapper.getUserByLimit(map);
        for (User user : users) {
    
    
            System.out.println(user);
        }
        sqlSession.close();
    }

2. Paging through RowBounds

mapper interface:

    //通过RowBounds实现分页
    List<User> getUserByRowBounds(RowBounds rowBounds);

In Mapper.xml:

    <select id="getUserByRowBounds" resultType="com.lu.pojo.User">
        select * from user
    </select>

testing method:

    @Test
    public void getUserByRowBounds(){
    
    
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        RowBounds rowBounds = new RowBounds(1, 2);
        List<User> users = userMapper.getUserByRowBounds(rowBounds);

        for (User user : users) {
    
    
            System.out.println(user);
        }
        sqlSession.close();
    }

3. Realize paging through the paging plugin pagehelper

Import dependencies in pom.xml:

     <dependency>
          <groupId>com.github.pagehelper</groupId>
          <artifactId>pagehelper</artifactId>
          <version>4.1.6</version>
      </dependency>

Add in mybatis-config.xml core configuration file:

<plugins>
    <plugin interceptor="com.github.pagehelper.PageHelper">
        <property name="dialect" value="mysql"/>
    </plugin>
</plugins>

mapper：

    //通过pagehelper分页插件实现
    List<User> getUserByPageHelper();

mapper.xml：

    <select id="getUserByPageHelper" resultType="com.lu.pojo.User">
        select * from user
    </select>

testing method:

Import first at the top of the class, otherwise PageHelper cannot be used

import com.github.pagehelper.PageHelper;

Write the test class:

    @Test
    public void getUserByPageHelper(){
    
    
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        PageHelper.startPage(1,3);
        List<User> users = userMapper.getUserByPageHelper();
        for (User user : users) {
    
    
            System.out.println(user);
        }
        sqlSession.close();
    }

Use Lombok steps

1. Install the Lombok plugin in IDEA.

Click File in the upper left corner —> Click Settings —> Select Pulgins —> Enter Lombok search —> Click Install to install. As shown below

2. Import the lombok jar package into the project

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.12</version>
    <scope>provided</scope>
</dependency>

3. Add annotations to the entity class

@NoArgsConstructor: Generate a parameterless constructor;

@AllArgsConstructor: Generate full parameter constructor;

@Data: Acting on the class, is a collection of the following annotations:

@ToString @EqualsAndHashCode @Getter @Setter @RequiredArgsConstructor