index.js

const {
  GraphQLID,
  GraphQLList,
  GraphQLString,
  GraphQLInt,
  DirectiveLocation,
  GraphQLDirective,
} = require('graphql');
const { SchemaDirectiveVisitor } = require('graphql-tools');
const { createHash } = require('crypto');

class UniqueIdDirective extends SchemaDirectiveVisitor {
  static getDirectiveDeclaration(directiveName = 'uid') {
    return new GraphQLDirective({
      name: directiveName,
      description: 'Generates unique ID based on specifics fields',
      locations: [DirectiveLocation.OBJECT],
      args: {
        from: {
          type: new GraphQLList(GraphQLString, GraphQLInt),
        },
      },
    });
  }

  visitObject(type) {
    const { name = 'uid', from } = this.args;

    const fields = type.getFields();

    if (name in fields) {
      throw new Error(`Conflicting field name ${name}`);
    }

    fields[name] = {
      name,
      type: GraphQLID,
      description: 'Unique ID',
      args: [],
      isDeprecated: false,
      resolve(object) {
        const hash = createHash('sha1');

        hash.update(type.name);

        from.forEach(fieldName => {
          hash.update(String(object[fieldName]));
        });

        return hash.digest('hex');
      },
    };
  }
}

module.exports = UniqueIdDirective;