在 Google 数据存储中，是否可以获取特定项目的光标？

Question

可以使用 Datastore.key 为元素生成新键：

const taskKey = datastore.key(['Task', 'sampleTask']);

当运行一个查询时，我们可能会得到一个endCursor可以用来得到下一个结果。

游标是一些 base64 编码的标记，其中包含项目 ID、种类和获取的最后一个元素的键，以及一些未知的二进制数据。

在给定项目键和种类+项目 ID 的情况下，是否可以 way/method 获取 base64 游标值？

Answer 1

不，这不可能。

或者我应该说（尝试）从实体本身获取游标没有多大意义，因为游标仅在获取它的原始查询的上下文中才有意义。来自 Limitations of cursors（强调我的）：

Cursors are subject to the following limitations:

• A cursor can be used only by the same application that performed the original query, and only to continue the same query. To use the cursor in a subsequent retrieval operation, you must reconstitute the original query exactly, including the same entity kind, ancestor filter, property filters, and sort orders. It is not possible to retrieve results using a cursor without setting up the same query from which it was originally generated.

也来自Cursors and data updates：

The cursor's position is defined as the location in the result list after the last result returned. A cursor is not a relative position in the list (it's not an offset); it's a marker to which Cloud Datastore can jump when starting an index scan for results.

Answer 2

如前所述，不可能从键推断游标，因为游标与查询相关联。但是，您可以按键过滤查询。例如。 select * 来自 Task where key > Key(Task, 'sampleTask')