Schema stitching

[hexwit]

Hello!

As I know there is no embedded functionality for schema stitching.
It is possible to merge two schemas, but process will fail if types with same name appears in both of them.

I need to merge specific types from both schemas. Merge their field definitions.
It is Query and Mutation types. Both of them exists in each schema.

How can I merge types with same names but different fields definitions into one type with
combined fields?

I investigated source code, SchemaParser and TypeDefinitionRegistry but didn't find suitable way to
merge type fields. I have feeling that I am looking at the wrong place.

Could you suggest how to solve my problem, and point me the direction where to dig.

Thanks in advance!

[bbakerman]

I think you will want to use SchemaTransformer and a custom visitor that takes the 2nd schema as input and "adds" fields to type as you encounter them, merging them by what ever algo you decide on.

There is currently no doco for this on https://www.graphql-java.com/ but I have a PR up for it here

graphql-java/graphql-java-page#50

and graphql.schema.SchemaTransformerTest is another place to show how to do it.

SchemaTransformer takes some grokking (with its return changeNode etc..) but its powerful on changing a complex immutable graph that is a schema

[rajdiran]

@bbakerman Please find the example schema below,

Module 1

type Query {
getUser(email: String!): PUserStatus! @auth
}
type PUserStatus{
status: USER_ONBOARDING_STATUS
}

X Module:

type Query {
getUser(email: String!) : PUserStatus
}

extend type Query {
getUser(email: String!) : PUserStatus!
}

type PUserStatus{
XUserStatus: XUserStatus
}

Y Module:

extend type Query {
getUser(email: String!) : PUserStatus!
}

type PUserStatus{
YUserStatus: YUserStatus
}

I have the router project which contains remote schema json for each module. It stitch those schema files and create the GraphqlSchema instance. It was working fine till graphql-java version 14. Now it is failing with 'Query' extension type [@-1:-1] tried to redefine field 'getUser' [@-1:-1]]

[dondonz]

That's correct, you are seeing this error message because your Query extension is attempting to redefine a field. This is not permitted in the specification, see this section: https://spec.graphql.org/draft/#sec-Objects.Type-Validation

For each field of an Object type:
The field must have a unique name within that Object type; no two fields may share the same name.

Perhaps the validation was added in between the versions you are using. An error is the expected behaviour.

Note, version 15 of GraphQL Java is quite out of date. The latest version is 21.x, I'd recommend using a more recent version for security updates.

[bbakerman]

Yeah only can defined type X and everything else needs to do extend type X

I have a beef with the spec in that this does not compose well - eg who gets to be the master definer of the type - any or all?

I would prefer it allowed any number of extend type X and they got added together (with field redefinition in place of course)

But this is not how the spec works and hence not how graphql-java now works.

[rajdiran]

@dondonz yes I am upgrading the graphql-java to the latest version which 21.x. I just tried different version to identity from which version it stopped working.

I understand that it is not permitted. is there a way to fix this without updating our existing schema? can custom schema stitch implementation help?

[dondonz]

Hi @rajdiran GraphQL Java implements the GraphQL specification, so if it's not permitted in the specification, the library will also not permit it. Perhaps others in the community have more information on schema stitching libraries, however in terms of pure GraphQL Java there isn't a way around it, it's validation to enforce the specification.