Federation Transform

If the original subgraph is not a federated subgraph that includes annotations and directives that conform to the Federation specification. You can use this transform to provide them and convert the subgraph to a federated subgraph.

💡

If you want to add @key directive in your subgraph, you need to be aware of Type Merging

How to use?

Let’s say you have the following subgraph;

type Product {
  id: ID!
  name: String!
  price: Float!
}
 
type Query {
  productById(id: ID!): Product
}

And you want to add @key directive to the Product type. Then you can add the following configuration to your mesh.config.ts file. But you need resolveReference to be able to resolve the reference, which is equivalent of __resolveReference resolver in regular Federation.

mesh.config.ts

import {
  createFederationTransform,
  defineConfig,
  loadGraphQLHTTPSubgraph
} from '@graphql-mesh/compose-cli'
 
export const composeConfig = defineConfig({
  subgraphs: [
    {
      sourceHandler: loadGraphQLHTTPSubgraph('myApi', {
        endpoint: 'http://localhost:4001/my-api'
      }),
      transforms: [
        createFederationTransform({
          // Schema Coordinates
          Product: {
            // Directive name
            key: {
              // Directive arguments
              fields: 'id',
              // Reference resolver (only for @key directive)
              resolveReference: {
                fieldName: 'productById'
              }
            }
          },
          // You can also add other directives
          Query: {
            extends: true
          }
        })
      ]
    }
  ]
})

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Learn more about other directives in Federation

Prune Schema Extensions