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https://github.com/0xr/graphql-transform-federation
Convert your existing GraphQL schema into a federated schema
https://github.com/0xr/graphql-transform-federation
graphql graphql-federation
Last synced: about 1 month ago
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Convert your existing GraphQL schema into a federated schema
- Host: GitHub
- URL: https://github.com/0xr/graphql-transform-federation
- Owner: 0xR
- Created: 2019-09-23T15:47:48.000Z (about 5 years ago)
- Default Branch: master
- Last Pushed: 2022-02-15T02:39:13.000Z (over 2 years ago)
- Last Synced: 2024-10-08T13:45:22.877Z (about 1 month ago)
- Topics: graphql, graphql-federation
- Language: TypeScript
- Homepage:
- Size: 250 KB
- Stars: 221
- Watchers: 12
- Forks: 24
- Open Issues: 8
-
Metadata Files:
- Readme: README.md
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README
# graphql-transform-federation
If you want to use
[GraphQL federation](https://www.apollographql.com/docs/apollo-server/federation/introduction/),
but you can't rebuild your current GraphQL schema, you can use this transform to
add GraphQL federation functionality to an existing schema. You need this when
you are using a managed GraphQL service or a generated schema which doesn't
support federation (yet).
If you are using apollo-server or another schema builder that supports
federation you don't need this transform you should
[add the federation directives](https://www.apollographql.com/docs/apollo-server/federation/implementing/)
directly.
This transform will add the resolvers and directives to conform to the
[federation specification](https://www.apollographql.com/docs/apollo-server/federation/federation-spec/#federation-schema-specification).
Much of the
[federation sourcecode](https://github.com/apollographql/apollo-server/tree/master/packages/apollo-federation)
could be reused ensuring it is compliant to the specification.
Check out the
[blogpost introducing graphql-tranform-federation](https://xebia.com/blog/graphql-federation-for-everyone/)
for more background information.
## Usage
You can use this transform on a local or a remote GraphQL schema. When using a
remote schema your service acts a middleware layer as shown in the diagram
above. Check the
[remote schema documentation](https://www.apollographql.com/docs/graphql-tools/remote-schemas/)
for how to get an executable schema that you can use with this transform.
The example below shows a configuration where the transformed schema extends an
existing schema. It already had a resolver `productById` which is used to relate
products between the two schemas. This example can be started using
[npm run example](#npm-run-example).
```typescript
import { transformSchemaFederation } from 'graphql-transform-federation';
import { delegateToSchema } from 'graphql-tools';
const schemaWithoutFederation = // your existing executable schema
const federationSchema = transformSchemaFederation(schemaWithoutFederation, {
Query: {
// Ensure the root queries of this schema show up the combined schema
extend: true,
},
Product: {
// extend Product {
extend: true,
// Product @key(fields: "id") {
keyFields: ['id'],
fields: {
// id: Int! @external
id: {
external: true
}
},
resolveReference({ id }, context, info) {
return delegateToSchema({
schema: info.schema,
operation: 'query',
fieldName: 'productById',
args: {
id,
},
context,
info,
});
},
},
});
```
To allow objects of an existing schema to be extended by other schemas it only
needs to get `@key(...)` directives.
```typescript
const federationSchema = transformSchemaFederation(schemaWithoutFederation, {
Product: {
// Product @key(fields: "id") {
keyFields: ['id'],
},
});
```
## API reference
```typescript
import { GraphQLSchema } from 'graphql';
import { GraphQLReferenceResolver } from '@apollo/federation/dist/types';
interface FederationFieldConfig {
external?: boolean;
provides?: string;
requires?: string;
}
interface FederationFieldsConfig {
[fieldName: string]: FederationFieldConfig;
}
interface FederationObjectConfig {
// An array so you can add multiple @key(...) directives
keyFields?: string[];
extend?: boolean;
resolveReference?: GraphQLReferenceResolver;
fields?: FederationFieldsConfig;
}
interface FederationConfig {
[objectName: string]: FederationObjectConfig;
}
function transformSchemaFederation(
schema: GraphQLSchema,
federationConfig: FederationConfig,
): GraphQLSchema;
```
## `npm run example`
Runs 2 GraphQL servers and a federation gateway to combine both schemas.
[Transformed-server](./example/transformed-server.ts) is a regular GraphQL
schema that is tranformed using this library. The
[federation-server](example/federation-server.ts) is a federation server which
is extended by a type defined by the `transformed-server`. The
[gateway](./example/gateway.ts) combines both schemas using the apollo gateway.
## `npm run example:watch`
Runs the example in watch mode for development.
## `npm run test`
Run the tests