如何描述Ebean的桥接表？ [英] How do I describe a bridge table to Ebean?

问题描述

让我说我有这些表：

ORDER: id
ITEM: id
ORDER_ITEM: order_id, item_id

表： ORDER_ITEM 是 ORDER 和 ITEM 。

如何将此三人组描述为 Ebean ？

How do I describe this threesome to Ebean?

我不想使用原始SQL，因此我仍然可以创建和更新这些实体。

I would prefer not to use raw SQL so that I can still create and update these entities.

更新周六11月9日02:32:40 UTC 2013

UPDATE Sat Nov 9 02:32:40 UTC 2013

好的，让我们解决这个问题更难，更能代表我的实际情况。列名称不符合约定：

Ok, lets make this problem harder and more representative of my actual situation. The column names dont fit the convention:

ORDER: order_number
ITEM: item_number
ORDER_ITEM: my_order, my_item

推荐答案

您不必自己创建特殊的桥接表，除非您想要其他字段除了外键。

You don't have to create special bridge table yourself unless you want to have other fields there except foreign keys.

在Order类中你应该定义字段：

In Order class you should define field:

@ManyToMany
public List<Item> items;

在物品类中：

@ManyToMany(mappedBy = "items")
public List<Order> orders;

Ebean将为您生成桥牌表。

And Ebean will generate bridge table for you.

此外：

您可以在两个类之间使用非对称关系类型：

You can have asymmetric relationship types between two classes:

@ManyToMany
@JoinTable(name="Order_Item")
public List<Item> items;

和

@ManyToOne
public Order order;

如果订单是商品<中的可选字段/ strong>并且您不希望在Item表中包含大量空字段。

in case when order is an optional field in Item and you don't want to have a lot of empty fields in Item table.

更新：

这对你有用。所有表名和列名现在都由注释明确命名：

This will work for you. All the table and column names are now explicitly named by annotations:

@Entity
@Table(name="ITEM")
public class Item extends Model {
    @Id
    @Column(name="item_number")
    public Integer id;

    @ManyToMany(mappedBy = "items")
    public List<Order> orders;
}

和

@Entity @Table(name="ORDER") public class Order extends Model {
    @Id
    @Column(name="order_number")
    public Integer id;

    @ManyToMany
    @JoinTable(name="ORDER_ITEM",
            joinColumns=@JoinColumn(name="my_order",referencedColumnName = "order_number"),
            inverseJoinColumns = @JoinColumn(name="my_item", referencedColumnName="item_number"))
    public List<Item> items; }

代码在这里： https://github.com/cosmolev/BridgeTable/tree/master/app/models

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