Mybatis Plus的删除操作内置了4种方法，我们来演示一下Mybatis Plus的删除操作。

1、根据主键ID删除指定单条数据

方法：

int deleteById(Serializable id);

代码：

    @Test    public void testDeleteById() {        System.out.println(("----- deleteById method test ------"));        List userList = userMapper.selectList(null);        System.out.println("-----删除前数据:");        userList.forEach(System.out::println);        userMapper.deleteById(5L);        System.out.println("-----删除后剩余数据:");        List userList2 = userMapper.selectList(null);        userList2.forEach(System.out::println);    }

前面已经输出了较多sql，我们这里简洁一些，只输出打印的数据

-----删除前数据:User(id=1, name=Jone, age=18, email=test1@baomidou.com)User(id=2, name=Jack, age=20, email=test2@baomidou.com)User(id=3, name=Tom, age=28, email=test3@baomidou.com)User(id=4, name=Sandy, age=21, email=test4@baomidou.com)User(id=5, name=Billie, age=24, email=test5@baomidou.com)-----删除后剩余数据:User(id=1, name=Jone, age=18, email=test1@baomidou.com)User(id=2, name=Jack, age=20, email=test2@baomidou.com)User(id=3, name=Tom, age=28, email=test3@baomidou.com)User(id=4, name=Sandy, age=21, email=test4@baomidou.com)

2、基于map中设置的key-value，删除一条或多条数据

基于map的删除，可以设置多个列作为条件，被匹配的数据都将被删除。

方法：

int deleteByMap(@Param(Constants.COLUMN_MAP) Map columnMap);

代码：

    @Test    public void testDeleteByMap() {        System.out.println(("----- deleteByMap method test ------"));        List userList = userMapper.selectList(null);        System.out.println("-----删除前数据:");        userList.forEach(System.out::println);        Map columnMap = new HashMap<>();        columnMap.put("Name","Tom");        userMapper.deleteByMap(columnMap);        System.out.println("-----删除后剩余数据:");        List userList2 = userMapper.selectList(null);        userList2.forEach(System.out::println);    }

输出：

-----删除前数据:User(id=1, name=Jone, age=18, email=test1@baomidou.com)User(id=2, name=Jack, age=20, email=test2@baomidou.com)User(id=3, name=Tom, age=28, email=test3@baomidou.com)User(id=4, name=Sandy, age=21, email=test4@baomidou.com)User(id=5, name=Billie, age=24, email=test5@baomidou.com)-----删除后剩余数据:User(id=1, name=Jone, age=18, email=test1@baomidou.com)User(id=2, name=Jack, age=20, email=test2@baomidou.com)User(id=4, name=Sandy, age=21, email=test4@baomidou.com)User(id=5, name=Billie, age=24, email=test5@baomidou.com)

3、基于一个实体作为条件，删除一条或多条数据

方法：

int delete(@Param(Constants.WRAPPER) Wrapper wrapper);

如果方法的参数设置为null，那么相当于全表删除

代码：

输出结果：

-----删除前数据:User(id=1, name=Jone, age=18, email=test1@baomidou.com)User(id=2, name=Jack, age=20, email=test2@baomidou.com)User(id=3, name=Tom, age=28, email=test3@baomidou.com)User(id=4, name=Sandy, age=21, email=test4@baomidou.com)User(id=5, name=Billie, age=24, email=test5@baomidou.com)==>  Preparing: DELETE FROM user ==> Parameters: <==    Updates: 5-----删除后剩余数据:==>  Preparing: SELECT id,name,age,email FROM user ==> Parameters: <==      Total: 0

我们从输出的日志看出：

==>  Preparing: DELETE FROM user ==> Parameters: <==    Updates: 5

sql是全表删除。

如果方法设置了实体作为参数，那就按照实体匹配，删除对应数据。

4、根据主键ID集合，批量删除数据

方法：

int deleteBatchIds(@Param(Constants.COLLECTION) Collection extends Serializable> idList);

代码：

    @Test    public void testDeleteBatchIds() {        System.out.println(("----- deleteBatchIds method test ------"));        List userList = userMapper.selectList(null);        System.out.println("-----删除前数据:");        userList.forEach(System.out::println);        List list = new ArrayList();        list.add(4L);        list.add(5L);        userMapper.deleteBatchIds(list);        System.out.println("-----删除后剩余数据:");        List userList2 = userMapper.selectList(null);        userList2.forEach(System.out::println);    }

输出：

-----删除前数据:User(id=1, name=Jone, age=18, email=test1@baomidou.com)User(id=2, name=Jack, age=20, email=test2@baomidou.com)User(id=3, name=Tom, age=28, email=test3@baomidou.com)User(id=4, name=Sandy, age=21, email=test4@baomidou.com)User(id=5, name=Billie, age=24, email=test5@baomidou.com)==>  Preparing: DELETE FROM user WHERE id IN ( ? , ? ) ==> Parameters: 4(Long), 5(Long)<==    Updates: 2-----删除后剩余数据:==>  Preparing: SELECT id,name,age,email FROM user ==> Parameters: <==    Columns: ID, NAME, AGE, EMAIL<==        Row: 1, Jone, 18, test1@baomidou.com<==        Row: 2, Jack, 20, test2@baomidou.com<==        Row: 3, Tom, 28, test3@baomidou.com<==      Total: 3User(id=1, name=Jone, age=18, email=test1@baomidou.com)User(id=2, name=Jack, age=20, email=test2@baomidou.com)User(id=3, name=Tom, age=28, email=test3@baomidou.com)