为什么在Ebean中使用java.util.List而不是java.util.Set

Question

I see that many examples use List for "many" relations, however, Set seems to better fulfil the role since lookup can happen in O(1) while the list search is O(N/2). Is there any reason why List is the preferred type to use?

Answer 1

只有在ManyToMany关系的情况下，重复才是重要的，在其他情况下，ORM也会处理List中的重复。

Answer 2

It depends on the situation you use.

1. Set contain no dublicates while you can hold dublicates in List.
2. List stores items in the inserted order.

Answer 3

List and Set are semantically different. Only looking at the lookup times is a bad idea and can lead to serious problems further down the line.

List can have duplicates, Set cannot.
List also guarantees access by index, which Set s do not. (Although some Set implementations of course might.)

Answer 4

Check yourself, Ebean's authors answered it already with details in article:

List Set Map or Collection?

You'll find there a sumarized description of each type and also comparison between chosen types.

Answer 5

我一直认为List保留了对底层数据库的查询结果的任何顺序。