Add total amount to pagination metadata

[hofermo]

What is missing?

When fetching all AAS / SM from a repository using the pagination it is not possible to know how many Elements are in the repository.
But for applications that want to show all AAS / SM / CDs in a their respective repository it helps to know how many elements are there to display e.g. a total amount of pages / elements or similar.
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How should it be fixed?

In the Paging Metadata a field with total elements could be added
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• I have signed the required Developer Certificate of Origin (DCO) already.

[mrentsch65]

Yes, this is really missing for practical applicabilitity of the AAS.

[sebbader-sap]

see also #354. Apparently, we didn't have the capa to include it in V3.1...

[aorzelskiGH]

I certainly agree that this would be nice on the client side.

On the server side the challenge is, that access rules and queries can lead to quite complex database queries.
My experience is, that for an amount of several million elements only pagenation "without total count" leads to a good performance.

[mjacoby]

I agree with @aorzelskiGH and want to add the following aspects

1. Computing a exact total count can be very expensive while computing an estimated total count is typically very cheap
2. We chose cursor-based paging over offset-based paging for better scalability with very large datasets, adding an exact total count would be diametrically opposed.
3. Cursor-based paging does not allow to directly skip to any page but you always have to consume one page after another from the beginning. So returning a total number would probably be rather cosmetic nature.

IMO a suitable approach would be make it optional for a server to return a count and also do not required it to be an exact count. Keep in mind, the count might change if the underlying data is updated and elements are removed while going through the pages.