graphql-directives-transform.ts

import { GraphQLSchema, printSchema } from 'graphql';
import { transformSchemaFederation } from 'graphql-transform-federation';
import { makeSchema } from '@nexus/schema';
import graphqlTypeJson from 'graphql-type-json';
import { Products } from '../resolvers/Products';
import { Product } from '../resolvers/Product';
import { types } from '../core/product';
import { DirectiveNode, ObjectTypeDefinitionNode, parse, visit, print } from 'graphql/language';

export async function buildNexusFederatedSchema(
): Promise<GraphQLSchema>  {

  const schema = makeSchema({
    types: [
        graphqlTypeJson,
        ...types,
        Product,
        Products
      ],
      outputs: {
        schema: __dirname + '/generated/search.graphql',
        typegen: __dirname + '/generated/search.ts'
      }
  });

  const addFederationDirectives = transformSchemaFederation(schema, {
    Query: {
      extend: true,
    },
    Product: {
      keyFields: ['id'],
    },
    BrandKeywordAggregationsOutput: {
      keyFields: ['key'],
    },
    BrandTermAggregationBucket: {
      keyFields: ['key'],
    },
    CategoryKeywordAggregationsOutput: {
      keyFields: ['key'],
    },
    CategoryTermAggregationBucket: {
      keyFields: ['key'],
    }
  });
  
  // At this point our federation directives have been appropriatetly added to the schema

  // Add a cache control directive
  const ast = parse(printSchema(addFederationDirectives));
  const addCachingDirectives = visit(ast, {
    ObjectTypeDefinition: {
      enter(node: ObjectTypeDefinitionNode) {
        if (node.name.value === 'Product') {
          const newDirective = createDirectiveNode('cacheControl', 'maxAge');
          return {
            ...node,
            directives: [...(node.directives || []), newDirective],
            kind: node.kind,
          };
        }
        return node;
      }
    }
  });
  
  console.log(print(addCachingDirectives))

  // At this point the cache control directive is appropriately set for product but the federation directives are no longer there
  return addCachingDirectives;
}

const createDirectiveNode = (
  name: string,
  argument: string
): DirectiveNode => {
  return {
    kind: 'Directive',
    name: { kind: 'Name', value: name },
    arguments: [{
      kind: 'Argument',
      name: { kind: 'Name', value: argument },
      value: { kind: 'IntValue', value: '300' },
    }],
  };
}