java Hibernate中bag tag的作用是什么？
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What is the use of bag tag in Hibernate?
提问by gokul
I need to know how to use the bag tag and what is the purpose of it?
我需要知道如何使用行李牌以及它的用途是什么？
回答by Damian Leszczyński - Vash
For collection mapping
用于集合映射
If your table does not have an index column, and you still wish to use List as the property type, you can map the property as a Hibernate < bag>. A bag does not retain its order when it is retrieved from the database, but it can be optionally sorted or ordered.
如果您的表没有索引列，并且您仍然希望使用 List 作为属性类型，则可以将该属性映射为 Hibernate < bag>。从数据库中检索包时不会保留其顺序，但可以选择对其进行排序或排序。
http://docs.jboss.org/hibernate/core/3.3/reference/en/html/collections.html
http://docs.jboss.org/hibernate/core/3.3/reference/en/html/collections.html
回答by McGin
From the API:
从API：
A bag is an unordered, unkeyed collection that can contain the same element multiple times. A bag permits duplicates, so it has no primary key. The Java collections API, curiously, has no Bag.
Bag 是一个无序、无键的集合，可以多次包含相同的元素。包允许重复，所以它没有主键。奇怪的是，Java 集合 API 没有 Bag。
回答by Rafael Borja
A short and simple answer:
一个简短的答案：
You don't need to use the <index>tag when mapping an unsorted Listand you also don't need an additional index column in database.
<index>映射未排序时不需要使用标记，List也不需要数据库中的额外索引列。
Unlike a List a Bag does not persist the order of its elements, but you can specify an order-byparameter to retrieve its elements in a specific order.
与 List 不同，Bag 不保留其元素的顺序，但您可以指定一个order-by参数以按特定顺序检索其元素。
