将对象列表映射到对象的ParameterizedRowMapper

Z时代
2024-01-10
分类：问答

我试图在ParameterizedRowMapper中设置父级列表，这是如何编写或处理的。我有两个对象，一个用于父对象，一个用于子对象，但是子对象包含一个List。每个子对象的父对象存储在数据库的单独表中，并且映射为1-许多。

父母记录的选择将在单独的ResultSet中完成。映射是否必须单独完成（ 单独的ParameterizedRowMapper

），如果是这样，我将如何编写这是如何编写

来容纳列表项的主要问题。

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

，但是我对此有疑问。在设置父级时，我是否将其集成到班级中？有人可以指导我如何正确地完成它

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

Public class Parent(){
 int pid;
String firstName;
String lastName;
..
//setters/getters
}

回答：

我将针对一个典型的一对多示例展示如何执行此操作，您可以将其调整为适合您的vo类/表。

订单类别

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

物品类别

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

每个类使用两个行映射器，然后使用结果集提取器将多行转换为一个顺序+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;
                }
            });
}