fix: top level relation

[zilto]

Related

• reimplementation of feat: top-level dlt.Dataset and dlt.Relation #2896 using more detailed commits and git mv
• chore: refactor dataset to be top level #2611

Features:

• top-level dlt.dataset()
• avoid conflicts between module dlt.dataset and function dlt.dataset() by naming module dlt._dataset instead.
  • AFAIU, this should be done in a follow-up PR
• public names dlt.Relation (at dlt.dataset.relation::Relation) and dlt.Dataset (at dlt.dataset.dataset::Dataset)
• Rename protocols dlt.Relation (at dlt.common.destination.dataset::Dataset) to dlt.common.destination.dataset::SupportsDataset (removed top-level); same for dlt.Dataset -> SupportsDataset
• backwards compatible APIs by pointing old imports to new ones
• deprecation warnings on type checking

Context

It does many useful things:

• top level dlt.dataset() to create / access datasets
• top-level module _dataset
• private module _dataset to avoid leaking interfaces
• sets public names to dlt.Relation and dlt.Dataset instead of dlt.destinations.dataset.relation.ReadableDBAPIRelation and dlt.destinations.dataset.dataset.ReadableDBAPIDataset
• fix typing issues (cast(), # type: ignore)
  I get that removing dlt.Dataset(Protocol) and dlt.Relation(Protocol) is controversial. I can add them back as SupportsDataset(Protocol) and SupportsRelation(Protocol).
  So if I start a new branch where the same changes are made but:

• call it dlt.dataset instead of dlt._dataset
  • (this will clash with top-level dlt.dataset() the dlt.Dataset factory; similar to the dlt.pipeline() issue we currently have "log" is not exported from module "dlt.pipeline.progress" #2934 )
• keep the protocols as SupportsDataset and SupportsRelation
• use git mv
  • I don't know if this will work, given the files still exist
    There will be no blockers?

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[zilto]

Closing because git mv doesn't improve GitHub diff view

[rudolfix]

this LGTM and we can merge. there's one question before we do it:

now the typing user sees is SupportsRelation, not Relation. same for Dataset.

in case of other top level objects: Pipeline, Destination (this is generic and typically a concrete type is seen) DltResourceandDltSource`

should we clean that up? I think we can do that in backward compatible way. I prefer simple names like Relation or Pipeline.