allocate_id总是返回正值吗？

Question

allocate_ids函数是否总是返回正值？ 或者它可以有时返回负值或零值吗？

Answer 1

在谷歌组评论人称为Stephen说关于db.model：

IDs are 64bit positive integers. If you allocate IDs for an entity called 'Sequence' you can use them for any other entity kind, including entities with parents which would otherwise use a unique range if auto allocated. IDs from 'Sequence' will be unique within your datastore, which is a superset of the requirement that IDs be unique per-entity group. However, you must always then use an ID from Sequence and never allow auto-allocation.

他似乎知道他在说什么。我无法找到另一个对数据存储的自动ID序列发生器，但在这种类似question这里的allocateids java的定义被链接到和它说，它可以抛出这个错误：

java.lang.IllegalArgumentException - If parent is not a complete key, if num is less than 1, or if num is greater than 1 billion.