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subschema composability rules #37

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@yaacovCR yaacovCR commented Jul 17, 2022

Comments welcome!

This is just an initial version, and has much room for improvement.

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@yaacovCR This is great. 👏 I've also been thinking about mergability and a common merging spec as a primary concern.

I've added some of my riffs as suggestions to your riffs 🙂

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to drop the number of used terms/simply, we can just use type composition
1. separate composability rules by execution strategy.

I am not sure if these should be separate in the final document, but separating helps me reason about them better within this draft stage.

2. remove discussion of runtime translation from composability rules

thats basically mixing the idea of "transforms" with composability.

For example, if there is a way of translating a missing enum value for a given subschema into an enum value that is present, we are basically transforming that subschema into a subschema that has the missing enum value by using a transformRequest method

Instead, let's make the composability rules strict and discuss separately the idea of transforms
@yaacovCR yaacovCR marked this pull request as ready for review August 8, 2022 18:10
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yaacovCR commented Aug 8, 2022

I have marked this PR as no longer DRAFT, as I have added section regarding all types. But it would certainly benefit from additional input and further revision. Comments are welcome.

@yaacovCR yaacovCR changed the title initial Subschema Composability riffs subschema composability rules Aug 8, 2022
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I had some more thoughts on "what does it mean to be composable?". This feels like it could be a whole separate topic, so I'm happy to move this to a discussion too.

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This is a great doc! I don't find the GitHub PR interface great for reviewing Markdown, so I wrote up a few thoughts in the discussion thread:
#35 (comment)

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benjie commented Aug 16, 2022

Minor markdown styling comment: please use

`backticksForCode`

and

*italics for references*

i.e. change

`Subschemas as remote GraphQL services`

to

*Subschemas as remote GraphQL services*

This follows the pattern used by spec-md.

yaacovCR and others added 2 commits August 18, 2022 15:13
Thanks @michaelstaib

Co-authored-by: Michael Staib <[email protected]>
Thanks @michaelstaib

Co-authored-by: Michael Staib <[email protected]>
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This follows the pattern used by spec-md.

@benjie any styling for definitions like for “composability” ?

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benjie commented Aug 20, 2022

@yaacovCR Indeed; if you're actually using spec-md then the paragraph that defines a term should start with :: and the term should be the first italicised term. Then references to it should use italics. Here's an example of request being defined in the spec:

https://github.com/graphql/graphql-spec/pull/949/files

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Should we go ahead and merge this since it's an RFC doc?

subschemas. This set of subschemas is then considered to be `composable`.
Inversely, it may be impossible to generate a valid composite schema containing
all of the GraphQL elements of a given set of subschemas; this set of subschemas
is considered `not composable`.
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Mathematically speaking, isn't it always possible to generate a composite schema from any two schemas A and B that implement the same version of the GraphQL spec and whose root types don't implement any interfaces by renaming every non-standard non-root type and directive in them, prefixing the names of all the fields on the root types with the name of the schema when adding them to the composite schema's root types, and replacing references to the root types in the sub-schemas with the respective composite schema's root types? Sure this becomes A + B rather than A & B - i.e. each field is resolved by exactly one subschema - but that's not really at odds with this paragraph?

I think the wording here needs to be more crisp... not sure how exactly - perhaps refer to the overlapping elements somehow?

Comment on lines +66 to +68
composite schema will yield request(s) against spec-compliant (or even
non-spec compliant) GraphQL subservices that are then merged into a single
request.
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The term "GraphQL" implies it's spec compliant. If they're not spec compliant then they're not GraphQL.

Also do you mean "result" rather than "request" here?

Suggested change
composite schema will yield request(s) against spec-compliant (or even
non-spec compliant) GraphQL subservices that are then merged into a single
request.
composite schema will yield request(s) against GraphQL subservices that
are then merged into a single result.

"build-time" composition, a single service executes the composite schema
without delegation to remote services tied to each subschema. Subschemas
exist for the purpose of code organization, but only the composite schema
exists at the time of execution.
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Suggested change
exists at the time of execution.
exists at the time of execution.
3. `Hybrid execution`: a combination of the above approaches.

Comment on lines +85 to +86
The below RFC examines composability separately for the above two forms of
composite schema execution.
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If you accept my Hybrid suggestion above, this will need adjusting.

Comment on lines +80 to +83
example, if a request against the composite schema must ultimately be translated
to request(s) against the still extant source subschemas, then the composition
must be -- in some sense -- reversed during execution, which is not always
possible, and introduces significant complexity.
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Under what circumstances would it be something that we'd do and yet it wouldnot be possible to reverse?

Suggested change
example, if a request against the composite schema must ultimately be translated
to request(s) against the still extant source subschemas, then the composition
must be -- in some sense -- reversed during execution, which is not always
possible, and introduces significant complexity.
example, if a request against the composite schema must ultimately be translated
to request(s) against the still extant source subschemas, then the composition
must be -- in some sense -- reversed during execution, which introduces
complexity.

to different types in the composite schema. Or, when metadata denotes types as
overlapping in the first instance, namespacing may be accomplished simply by
adjusting the existing metadata or via additional metadata. Finally, a new
namespace construct may be introduced into the GraphQL specification itself such
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Suggested change
namespace construct may be introduced into the GraphQL specification itself such
namespace construct might be introduced into the GraphQL specification itself such

Comment on lines +130 to +131
1. Overlapping enum types where the types define identical sets of values can
always be composed, as they are identical in all subschemas.
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A risk of this, however, is if you compose them as equivalent but it turns out they have different meanings and they later wish to diverge. For example:

enum Can {
  DUCK
}

might evolve in one schema (capabilities) to enum Can { DUCK RUN } 🏃 or in another (canned goods) to enum Can { DUCK BEANS } 🥫

Comment on lines +132 to +133
2. Subschemas with overlapping enum types where the disparate types define
different value sets are only sometimes composable.
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Suggested change
2. Subschemas with overlapping enum types where the disparate types define
different value sets are only sometimes composable.
2. Subschemas with overlapping enum types where the disparate types define
different value sets are sometimes composable.

Comment on lines +216 to +217
1. Overlapping interface types cannot be composed if any overlapping fields
cannot be composed, see below.
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May need a comment on the interfaces that the interface implements.

Comment on lines +179 to +180
1. Overlapping object types cannot be composed if any overlapping fields cannot
be composed, see below.
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Needs a comment on the interfaces the object type implements too.

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During our call today we outlined where we're going, and sounds like composability rules are on the horizon again.

@michaelstaib @martijnwalraven We could use Yaacov's PR here as a discussion starter.

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in the rfc there were several times mentioned ways to influence schema objects composability

a method of composition may be devised in which elements in
different subschemas with different names are mapped to the same element in the
composite schema via some set of guiding metadata.

As far as I understood, it must be some directives, which allow merging or do merging implicitly? May small paragraph on directives which supply merging will be useful there?

(please just ignore my input, if it doesn't help!)

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6 participants