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bag标签，它的目的是什么？
3 个解决方案
#1
8
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，并且您仍希望使用List作为属性类型，则可以将该属性映射为Hibernate
。从数据库中检索包时，包不会保留其顺序，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
#2
3
From the API:
来自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是一个无序的，无键的集合，可以多次包含相同的元素。一个包允许重复，所以它没有主键。奇怪的是，Java集合API没有Bag。
#3
2
A short and simple answer:
一个简短而简单的答案：
You don't need to use the <index> tag when mapping an unsorted List and you also don't need an additional index column in database.
映射未排序的List时不需要使用
Unlike a List a Bag does not persist the order of its elements, but you can specify an order-by parameter to retrieve its elements in a specific order.
与List不同，Bag不会保持其元素的顺序，但您可以指定order-by参数以按特定顺序检索其元素。
#1
8
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，并且您仍希望使用List作为属性类型，则可以将该属性映射为Hibernate
。从数据库中检索包时，包不会保留其顺序，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
#2
3
From the API:
来自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是一个无序的，无键的集合，可以多次包含相同的元素。一个包允许重复，所以它没有主键。奇怪的是，Java集合API没有Bag。
#3
2
A short and simple answer:
一个简短而简单的答案：
You don't need to use the <index> tag when mapping an unsorted List and you also don't need an additional index column in database.
映射未排序的List时不需要使用
Unlike a List a Bag does not persist the order of its elements, but you can specify an order-by parameter to retrieve its elements in a specific order.
与List不同，Bag不会保持其元素的顺序，但您可以指定order-by参数以按特定顺序检索其元素。