3.12mybatisplus学习

1.自动填充

2.乐观锁

当要更新一条记录的时候，希望这条记录没有被别人更新，也就是说实现线程安全的数据更新 

当需要修改时，自动的实现version加1

3.使用mp进行简单查询

//1使用mp分页插件进行分页查询
@Test
public void testSelect3() throws Exception{
    Page page = new Page<>(1,3);
    Page userPage = userMapper.selectPage(page, null);
    //返回对象得到分页所有数据
    long pages = userPage.getPages(); //总页数
    long current = userPage.getCurrent(); //当前页
    List records = userPage.getRecords(); //查询数据集合
    long total = userPage.getTotal(); //总记录数
    boolean hasNext = userPage.hasNext();  //下一页
    boolean hasPrevious = userPage.hasPrevious(); //上一页

    System.out.println(pages);
    System.out.println(current);
    System.out.println(records);
    System.out.println(total);
    System.out.println(hasNext);


}

//2简单的根据id查询
@Test
public void testSelect1() throws Exception{
    List users = userMapper.selectBatchIds(Arrays.asList(1, 2, 3));
    System.out.println(users);

}
//3使用map进行简单的多个条件查询
@Test
public void testSelectt2() throws Exception{
   Map columnMap = new HashMap<>();
   columnMap.put("name", "jack");
   columnMap.put("age", 20);
    List users = userMapper.selectByMap(columnMap);
    System.out.println(users);

}

4.删除操作

删除与实现逻辑删除

//1  id删除
@Test
public void testDeleteId() throws Exception{
    int i = userMapper.deleteById(5);
    System.out.println(i);
}
//2  批量删除
@Test
public void testDeleteBatchIds(){
    int deleteBatchIds = userMapper.deleteBatchIds(Arrays.asList( 2, 3));
    System.out.println(deleteBatchIds);

}
//3  简单条件删除
@Test
public void testDeleteByMap() throws Exception{
    HashMap map = new HashMap();
    map.put("name", "Sandy");
    map.put("age",21);
    int i = userMapper.deleteByMap(map);
    System.out.println(i);

}

逻辑删除

可以通过mp的自动填充对deleted进行初始化 

5.条件构造器查询

wrapper

查询方式

6.git