1. BaseMapper：

   1. MyBatis-Plus 中的基本 CURD 在内置的 BaseMapper 中都已得到了实现，我们可以直接使用接口，接口如下：

      //
      // Source code recreated from a .class file by IntelliJ IDEA
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      package com.baomidou.mybatisplus.core.mapper;
      
      import com.baomidou.mybatisplus.core.conditions.Wrapper;
      import com.baomidou.mybatisplus.core.metadata.IPage;
      import com.baomidou.mybatisplus.core.toolkit.CollectionUtils;
      import com.baomidou.mybatisplus.core.toolkit.ExceptionUtils;
      import java.io.Serializable;
      import java.util.Collection;
      import java.util.List;
      import java.util.Map;
      import org.apache.ibatis.annotations.Param;
      
      public interface BaseMapper<T> extends Mapper<T> {
          int insert(T entity);
      
          int deleteById(Serializable id);
      
          int deleteById(T entity);
      
          int deleteByMap(@Param("cm") Map<String, Object> columnMap);
      
          int delete(@Param("ew") Wrapper<T> queryWrapper);
      
          int deleteBatchIds(@Param("coll") Collection<?> idList);
      
          int updateById(@Param("et") T entity);
      
          int update(@Param("et") T entity, @Param("ew") Wrapper<T> updateWrapper);
      
          T selectById(Serializable id);
      
          List<T> selectBatchIds(@Param("coll") Collection<? extends Serializable> idList);
      
          List<T> selectByMap(@Param("cm") Map<String, Object> columnMa