How to use firebase timestamp with graphql nest js?

Question

All dates in firebase are stored as timestamps, no matter how do you store them: as ISO string, or just as new Date().

But I don't want to send firestore.Timestamp instance on the client side, so I need to somehow serialize it.

What are the options? How can I send only ISO string, or unix time?

Answer 1

1. Simpliest and dumbest solution

Store date using unix time:

const newItem = {
  ...,
  createdAt: Date.now(),
};

itemsCollection.add(newItem);

this way it will be stored as plain number and it can be converted back to normal date using new Date()

2. Use third-party library (worked only for schema first approach for me)

firestore-graphql-scalars contains scalar type definitions and resolvers for firebase timestamp

If you are going for scheme-first approach it works perfectly fine, but I couldn't find a way to use it in Nest JS GraphQL code first approach

3. Define new scalar type yourself (code first approach implementation)

At the end I came up with this scalar using code first approach:

@Scalar('FirebaseTimestamp')
export class FirebaseTimestampScalar implements CustomScalar<number, admin.firestore.Timestamp> {
  description = 'Firebase timestamp';

  parseValue(milliseconds: number): admin.firestore.Timestamp {
    return admin.firestore.Timestamp.fromMillis(milliseconds); // value from the client
  }

  serialize(timestamp: admin.firestore.Timestamp): number {
    return timestamp.toMillis(); // value sent to the client
  }

  parseLiteral(ast: ValueNode): admin.firestore.Timestamp {
    if (ast.kind === Kind.INT) {
      return admin.firestore.Timestamp.fromMillis(Number(ast.value));
    }

    return null;
  }
}

and in data type:

@ObjectType()
export class DocumentMeta implements IDocumentMeta {
  @Field(() => ID)
  createdBy: string;
  @Field(() => ID)
  updatedBy: string;
  @Field(() => FirebaseTimestampScalar)
  createdAt: Date;
  @Field(() => FirebaseTimestampScalar)
  updatedAt: Date;
}

P.S. Don't forget to add this scalar to resolver module providers

@Module({
  providers: [
    ...resolvers,
    FirebaseTimestampScalar,
  ],
})
export class ResolversModule {}

you still have to convert it to date on client side, but on server side it remains as Timestamp instance, so it looks a little bit cleaner

5. Worth mentioning, but maybe not so useful

If you still think you need to get Timestamp 'as is' on client-side, you can stringify timestamp object, and parse it on client

You can do it yourself or using graphql-type-json