docs: public String selectByPrimaryKey(MappedStatement ms) {
          final Class<?> entityClass = getEntityClass(ms);
          //将返回值修改为实体类型
          setResultType(ms, entityClass);
          StringBuilder sql = new StringBuilder();
          sql.append(SqlHelper.selectAllColumns(entityClass));
          sql.append(SqlHelper.fromTable(entityClass, tableName(entityClass)));
          sql.append(SqlHelper.wherePKColumns(entityClass));
          return sql.toString();
      }