@gqlts/cli/src/render/typeMap/unionType.ts

Generate a client sdk from your GraphQl API

import { GraphQLUnionType } from 'graphql';
import { flatten, uniq } from 'lodash';

import { RenderContext } from '../common/RenderContext';
import type { FieldMap } from './types';

export function unionType(type: GraphQLUnionType, _: RenderContext) {
  const types = type.getTypes();
  const typeObj: FieldMap<string> = types.reduce<FieldMap<string>>((r, t) => {
    r[`on_${t.name}`] = { type: t.name };
    return r;
  }, {});

  const commonInterfaces = uniq(flatten(types.map((x) => x.getInterfaces())));
  commonInterfaces.forEach((t) => {
    typeObj[`on_${t.name}`] = { type: t.name };
  });

  typeObj.__typename = { type: 'String' };

  return typeObj;
}