Question

我正在尝试在ParameterizedRowMapper中设置父列表，如何编写或接近它。我有两个对象，一个用于父级，一个用于子级，但子级包含List。每个子级的父级存储在数据库中的单独表中，映射为1 - 多个。

父项记录的选择将在单独的ResultSet中完成。是否必须单独完成映射（单独的ParameterizedRowMapper ），如果是这样，我将如何编写 ParameterizedRowMapper 这是主要关注 ParameterizedRowMapper 是为了容纳列表项而编写的。

了ParameterizedRowMapper

public static class ChildrenMapper implements ParameterizedRowMapper<Children>{         

         public Children mapRow(ResultSet rs, int rowNum) throws SQLException {
                Children child = new Children();
                child.setFirstName(rs.getString("firstName"));
                child.setLastName(rs.getString("lastName"));
                    //a child can have many Parents or gaurdians
                child.setParent(List<Parent>);                  

                return child;
            }       
    }

根据我的研究，我发现我需要使用 ResultSetExtractor ，但是我对使用它有疑问。在设置父级时，我是否将它集成到课程中？有人可以指导我如何以正确的方式完成

Children.java

Public class Children(){
int cid;
String firstName;
String lastName;
List<Parent>parents;
..

//getters/setters

}

Parent.java

Public class Parent(){
 int pid;
String firstName;
String lastName;
..

//setters/getters
}

Answer 1

我将展示如何为规范的1对多示例执行此操作，您可以将其调整为您的vo类/表。

订单类

public class Order {
    private Long orderId;
    private String user;
    private List<LineItem> items;
    // Getter / setter omitted
}

项目类

public class LineItem {
    private Long lineItemId;
    private String product;
    private int quantity;
    // Getter / setter omitted
}

为每个类使用两个rowmappers，然后使用结果集提取器将多行转换为一个订单+订单项

OrderRepository

public final static RowMapper<Order> orderMapper = ParameterizedBeanPropertyRowMapper.newInstance(Order.class);
public final static RowMapper<LineItem> lineItemMapper = ParameterizedBeanPropertyRowMapper.newInstance(LineItem.class);

public Order findOrderWithItems(Long orderId) {
    return jdbcTemplate.query("select * from orders, line_item "
            + " where orders.order_id = line_item.order_id and orders.order_id = ?", 
            new ResultSetExtractor<Order>() {
        public Order extractData(ResultSet rs) throws SQLException, DataAccessException {
            Order order = null;
            int row = 0;
            while (rs.next()) {
                if (order == null) {
                    order = orderMapper.mapRow(rs, row);
                }
                order.addItem(lineItemMapper.mapRow(rs, row));
                row++;
            }
            return order;
        }

    }, orderId);
}

public List<Order> findAllOrderWithItmes() {
    return jdbcTemplate.query("select * from orders, line_item "
            + " where orders.order_id = line_item.order_id order by orders.order_id",
            new ResultSetExtractor<List<Order>>() {
                public List<Order> extractData(ResultSet rs) throws SQLException, DataAccessException {
                    List<Order> orders = new ArrayList<Order>();
                    Long orderId = null;
                    Order currentOrder = null;
                    int orderIdx = 0;
                    int itemIdx = 0;
                    while (rs.next()) {
                        // first row or when order changes
                        if (currentOrder == null || !orderId.equals(rs.getLong("order_id"))) {
                            orderId = rs.getLong("order_id");
                            currentOrder = orderMapper.mapRow(rs, orderIdx++);
                            itemIdx = 0;
                            orders.add(currentOrder);
                        }
                        currentOrder.addItem(lineItemMapper.mapRow(rs, itemIdx++));
                    }
                    return orders;
                }

            });
}

ParameterizedRowMapper将对象列表映射到对象

1 个答案: