mybatis plus 只保存list中已经修改过的
时间: 2023-07-23 20:45:05 浏览: 35
可以使用 MyBatis Plus 提供的 `updateBatchById` 方法来实现只保存 list 中已经修改过的数据。该方法会自动判断哪些数据需要进行更新,哪些数据不需要更新。
具体实现方式如下:
1. 首先,需要将需要更新的数据存入一个 List 中,并对需要进行更新的数据进行修改。
2. 调用 `updateBatchById` 方法,传入上一步中的 List。
示例代码如下:
```
// 假设需要更新的数据存储在 list 中
List<User> list = new ArrayList<>();
User user1 = new User();
user1.setId(1L);
user1.setUsername("new_name1");
list.add(user1);
User user2 = new User();
user2.setId(2L);
user2.setUsername("new_name2");
list.add(user2);
// 调用 updateBatchById 方法,实现只保存已经修改过的数据
userService.updateBatchById(list);
```
注意,上述代码中的 `User` 类需要继承 `BaseEntity` 类,以便 MyBatis Plus 能够自动识别出哪些数据需要进行更新。同时,在 `User` 类中需要定义对应的属性和方法,以便能够正确地映射数据库中的字段。
相关问题
mybatis plus 批量保存 List<Map
<Mybatis-Plus>提供了一个方法`insertBatchSomeColumn(List<T> entityList)`,可以实现批量保存实体类列表,同时支持批量保存时指定需要插入的字段。
但是,如果要保存的数据是`List<Map<String, Object>>`类型的,需要做一些额外的处理:
1. 自定义一个Mapper接口,定义一个方法`batchInsert(List<Map<String, Object>> list)`。
2. 在Mapper.xml文件中实现`batchInsert`方法,使用Mybatis-Plus提供的`insertBatchSomeColumn`方法进行批量保存。
下面是示例代码:
Mybatis-Plus版本:3.4.1
Java代码:
```java
public interface CustomMapper {
void batchInsert(List<Map<String, Object>> list);
}
```
Mapper.xml代码:
```xml
<mapper namespace="com.example.CustomMapper">
<insert id="batchInsert" parameterType="java.util.List">
insert into table_name
<trim prefix="(" suffix=")" suffixOverrides=",">
<foreach collection="list[0].keySet()" item="column">
<if test="column != null">
${column},
</if>
</foreach>
</trim>
values
<foreach collection="list" item="item" separator=",">
<trim prefix="(" suffix=")" suffixOverrides=",">
<foreach collection="item.entrySet()" item="entry">
<if test="entry.value != null">
#{entry.value},
</if>
</foreach>
</trim>
</foreach>
</insert>
</mapper>
```
使用示例:
```java
@Autowired
private CustomMapper customMapper;
@Test
void testBatchInsert() {
List<Map<String, Object>> list = new ArrayList<>();
Map<String, Object> map1 = new HashMap<>();
map1.put("column1", "value1");
map1.put("column2", 2);
Map<String, Object> map2 = new HashMap<>();
map2.put("column1", "value3");
map2.put("column2", 4);
list.add(map1);
list.add(map2);
customMapper.batchInsert(list);
}
```
注意事项:
1. `list`中每个元素必须包含相同的键值对,否则会保存失败。
2. `list`中的键值对的顺序可以不同,因为在Mapper.xml文件中会根据键名动态生成SQL语句。
3. 对于需要自增的主键,可以使用MySQL的`INSERT INTO...ON DUPLICATE KEY UPDATE`语句实现批量保存和更新。
mybatis plus selectList
MyBatis Plus is an enhanced version of the MyBatis framework, providing additional features and simplifying the development process. To execute a SELECT query using MyBatis Plus' selectList method, you need to follow these steps:
1. Define a mapper interface: Create an interface that extends the BaseMapper interface provided by MyBatis Plus. This interface will define the methods for performing database operations.
2. Write a SQL query: Use the @Select annotation provided by MyBatis Plus to define the SQL query for selecting records from the database. Alternatively, you can use the QueryWrapper or LambdaQueryWrapper to build dynamic queries.
3. Invoke the selectList method: In your service or controller class, inject the mapper interface and use its selectList method to execute the query. Pass in the necessary parameters, if any, and retrieve the result as a list of objects.
Here's an example of how you can use the selectList method in MyBatis Plus:
```java
// Step 1: Define a mapper interface
public interface UserMapper extends BaseMapper<User> {
@Select("SELECT * FROM users")
List<User> getAllUsers();
}
// Step 2: Write a SQL query
// Step 3: Invoke the selectList method
@Autowired
private UserMapper userMapper;
public List<User> getAllUsers() {
return userMapper.getAllUsers();
}
```
In this example, we define a UserMapper interface that extends BaseMapper<User>. We define the getAllUsers method with an SQL query using the @Select annotation. Finally, we inject the UserMapper interface and invoke the getAllUsers method to retrieve all users from the database.
Remember to configure MyBatis Plus properly in your application's configuration file and set up the database connection details.