Support to render `SlicedModel` from `Slice` via a dedicated `RepresentationModelAssembler`

[spring-projects-issues]

Oliver Drotbohm opened DATACMNS-845 and commented

From the original ticket in Spring HATEOAS:

Sometimes we cannot have information such as the total elements and total pages of a request, that's where we're using a Slice instead of a Page. But the PagedResourcesAssembler does not allow to convert a Slice to a Resource. It would be great to add a toResource(Slice<T> entity) method, or even add SlicedResourcesAssembler class.

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Reference URL: spring-projects/spring-hateoas#443

2 votes, 4 watchers

[asjp1970]

Hi Oliver,
I've seen that the parent issue of this one is closed and this one has remained open for a while, last update being end of last year after nearly 4 years.
I wonder if this has any chance to get into HATEOAS because I am returning pages of a large set of entities and it's becoming a heavy operation over time; a possible improvement would be to return slice... But as we are using HATEOAS we are a bit tied to pages because clients are consuming the hypermedia.
Have checked some of the last release notes and have not seen anything about Slice support: is this still being considered a candidate for your backlog?
Thanks.
/Alberto

[bigjoe-memooria]

Same issue here: we are exposing a MongoDB collection with 1M+ elements via Spring HATEOAS and Page has become utterly inefficient due to the -useless in this case- total page number called through a count().
A Slice support would perhaps mitigate this huge performance bottleneck.

[odrotbohm]

As a workaround it should be possible to issue repository methods returning a Slice and adding navigation links pointing to the previous and potentially next slice manually. Wouldn't mind to see such code wrapped into a SliceRepresentationModelAssembler effectively producing a CollectionModel<T> with the aforementioned links added in a pull request.

[bigjoe-memooria]

You're right, will look into it 👍

[mschout]

This bothered me enough I took a stab at solving it. Added SlicedModel to spring-hateoas and added SlicedResourcesAssembler plus injection to spring-data-commons. The HATEOAS MR needs to get merged first as the resources assembler needs that to be present in hateoas. Hopefully I did everything correctly 🤞