Offset based paging in GraphQL integration

[david-kubecka]

I would like to migrate our existing app from a Spring Data + GraphQL-specific-DTOs setup to Blaze persistence, utilizing EntityViews instead of the DTOs. Using the documentation (btw it's great!) + example projects I was able to figure out most of the stuff with the exception of paging.

Currently, we use the classic offset-based paging and pass Pageable into the repository findAll methods. While I would like to utilize the provided Keyset pagination in the future, this is a breaking change of the API and as such, I would like to postpone that until later. The question therefore is: how I can use the offset paging mechanism with the GraphQL integration?

From the docs it seems that all paging input data are encapsulated in the DataFetchingEnvironment, which however comes from the client request and doesn't seem to be modifiable. Is there any other way how to simply pass offset/limit parameters to the entity view setting? E.g. similarly to EntityViewSetting.create(CatView.class, 0, 10) but with the ability to pass DataFetchingEnvironment?

[david-kubecka]

Inspecting the source code I think I see the solution now. There is this public method in GraphQLEntityViewSupport:

public <T> EntityViewSetting<T, CriteriaBuilder<T>> createSetting(Class<T> entityViewClass, DataFetchingEnvironment dataFetchingEnvironment, String elementRoot, KeysetPage keysetPage, Integer first, Integer last, Integer offset)

where I can simply pass first and offset (other paging related params will be null).

[beikov]

Actually, even the createPaginatedSetting(DataFetchingEnvironment dataFetchingEnvironment) will work. If you read the documentation, you will see that it expects fields with certain names in the GraphQL query, from which it will read the pagination values.

[david-kubecka]

Yeah, I've seen that. But that will require an API change which - as I said - I want to avoid for now. Correct me if I'm wrong.

[beikov]

You mean that you have chosen different names for your offset/limit parameters? If so, the only sensible way for you to model this would be by extending GraphQLEntityViewSupportFactory and construct the GraphQLEntityViewSupport with the custom names. I see that it's a bit hard to do that right now. I can extract a method for constructing the GraphQLEntityViewSupport so that you only have to override that one. Would that help in your case?

[david-kubecka]

Actually, we wrap offset/limit into a specific type in the input so you would rather have to provide a more general PagingInputExtractor interface which will let us extract the wrapper paging type into scalars. But that seems to be quite an overkill for me, so if you don't see any problem with my suggested option I will go in that direction and try to switch to the supported keyset paging mechanism ASAP.

[beikov]

Yeah that's an overkill. I tried to rely on what the Relay specification requires, as this seemed most natural to me. Thanks for the clarification.