MyBatis-Plus paging query

MyBatis-Plus paging query

MySQL-User data table information

id	name	age	email	create_time	update_time
1	Our	18	[email protected]	2022-02-22 08:56:15	2022-02-01 08:56:20
2	Jack	20	[email protected]	2022-02-16 09:00:44	2022-02-17 09:00:48
3	Tom	28	[email protected]	2022-02-10 09:00:52	2022-02-19 09:00:57
4	Sandy	21	[email protected]	2022-02-14 09:01:02	2022-02-21 09:01:06
5	Billie	24	[email protected]	2022-02-09 09:01:13	2022-02-18 09:01:19
6	YCloud	22	[email protected]	2022-02-22 09:02:19	2022-02-22 09:02:23
7	TrainingL	23	[email protected]	2022-02-01 09:02:57	2022-02-10 09:03:01
8	Demo	22	[email protected]	2022-02-04 09:03:24	2022-02-14 09:03:28
9	Geoffrey	30	[email protected]	2022-01-12 09:04:30	2022-02-10 09:04:34
10	George	27	[email protected]	2022-02-09 09:05:09	2022-02-12 09:05:12
11	William	42	[email protected]	2022-02-22 09:05:45	2022-02-22 09:05:47
12	Glen	30	[email protected]	2022-02-08 09:07:03	2022-02-28 09:07:06

1. MyBatis-Plus query operation

1. Query records by id primary key (uniqueness):T selectById(Serializable id)

//测试查询
@Test
public void testSelectById(){
    
    
    //通过id=1L主键查询记录(唯一性)
    User user = userMapper.selectById(1L);
    System.out.println(user);
}

2. Batch query records through id collection:List<T> selectBatchIds(Collection idList)

//测试批量查询
@Test
public void testSelectByBatchId(){
    
    
    List<Integer> ids = Arrays.asList(1, 2, 3);
    //通过id集合查询记录
    List<User> users = userMapper.selectBatchIds(ids);
    for (User user : users) {
    
    
        System.out.println(user);
    }
}

3. Query one of the conditions (using the map operation):selectByMap()

//按条件查询之一：使用map操作
@Test
public void testSelectByMap(){
    
    
    HashMap<String, Object> map = new HashMap<>();
    //自定义要查询的条件
    map.put("name", "YCloud");
    map.put("age", 22);
    //返回值是一个列表，因为可能返回多条记录
    List<User> users = userMapper.selectByMap(map);
    for (User user : users) {
    
    
        System.out.println(user);
    }
}

2. Paging query (how to use?)

1. Configure the paging plugin

@Configuration
public class MyBatisPlusConfig {
    
    
    @Bean
    public PaginationInterceptor paginationInterceptor() {
    
    
        return new PaginationInterceptor();
    }
}

In the high version of SpringBoot, this configuration method is outdated, so another way of writing MybatisPlusInterceptor is used , as follows:

@Configuration
public class MyBatisPlusConfig {
    
    
    //分页插件——新的分页插件，旧版本PaginationInterceptor失效了
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor(){
    
    
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }
}

2. Use the Page object directly

method	describe
getRecords()	Query the data records of the current page, the return type is a list
getTotal()	total number of records checked
getSize()	page size
getPages()	total pages
hasPrevious()	Whether the current page has a previous page
hasNext()	Whether the current page has a next page
getCurrent()	Returns the current page number

//测试分页查询
@Test
public void testPage(){
    
    
    //参数一：当前页，参数二：页面大小
    //使用了分页插件之后，所有的分页操作也变得简单
    Page<User> page = new Page<>(1, 5);
    userMapper.selectPage(page, null);

    List<User> records = page.getRecords();
    for (User user : records) {
    
    
        System.out.println(user);
    }
    System.out.println("记录总数:" + page.getTotal());
    System.out.println("每一页的大小:" + page.getSize());
    System.out.println("是否有上页:" + page.hasPrevious());
    System.out.println("当前页:" + page.getCurrent());
    System.out.println("总页数:" + page.getPages());
    System.out.println("是否有下页:" + page.hasNext());
}

Console print log:

==>  Preparing: SELECT COUNT(*) FROM user
==> Parameters: 
<==    Columns: COUNT(*)
<==        Row: 12
<==      Total: 1
==>  Preparing: SELECT id,name,age,email,create_time,update_time FROM user LIMIT ?
==> Parameters: 5(Long)
<==    Columns: id, name, age, email, create_time, update_time
<==        Row: 1, Jone, 18, [email protected], 2022-02-22 08:56:15, 2022-02-01 08:56:20
<==        Row: 2, Jack, 20, [email protected], 2022-02-16 09:00:44, 2022-02-17 09:00:48
<==        Row: 3, Tom, 28, [email protected], 2022-02-10 09:00:52, 2022-02-19 09:00:57
<==        Row: 4, Sandy, 21, [email protected], 2022-02-14 09:01:02, 2022-02-21 09:01:06
<==        Row: 5, Billie, 24, [email protected], 2022-02-09 09:01:13, 2022-02-18 09:01:19
<==      Total: 5

It can be seen that the bottom layer of the paging plugin also performs paging through database limit query.