allocate_id總是返回正值嗎？

Question

allocate_ids函數是否總是返回正值？ 或者它可以有時返回負值或零值嗎？

Answer 1

在谷歌組評論人稱爲Stephen說關於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.

他似乎知道他在說什麼。我無法找到另一個對數據存儲的自動ID序列發生器，但在這種類似question這裏的allocateids java的定義被鏈接到和它說，它可以拋出這個錯誤：

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