Having some issues with creating object type for generic interface

[jnssnmrcs]

Hi!

I'm trying to create the following function for creating a object type for generic input, but I cannot get it to work:

interface PageInfo {
  hasPreviousPage: boolean;
  hasNextPage: boolean;
  startCursor: string;
  endCursor: string;
}

interface Edge<T> {
  node: T;
  cursor: string;
}

interface Connection<T> {
  edges: Edge<T>[];
  pageInfo: PageInfo;
}

const PageInfo = builder.objectRef<PageInfo>('PageInfo').implement({
  fields: (t) => ({
    hasPreviousPage: t.exposeBoolean('hasPreviousPage'),
    hasNextPage: t.exposeBoolean('hasNextPage'),
    startCursor: t.field({ type: 'Cuid', nullable: true, resolve: (i) => i.startCursor }),
    endCursor: t.field({ type: 'Cuid', nullable: true, resolve: (i) => i.endCursor }),
  }),
});

export const buildConnectionType = <T>(name: string, nodeType: ObjectRef<T>) => {
  const Edge = builder.objectRef<Edge<T>>(`${name}Edge`).implement({
    fields: (t) => ({
      node: t.field({
        resolve: (parent) => parent.node,
        type: nodeType,
      }),
      cursor: t.field({
        resolve: (parent) => parent.cursor,
        type: 'Cuid',
      }),
    }),
  });

  const Connection = builder.objectRef<Connection<T>>(`${name}Connection`).implement({
    fields: (t) => ({
      edges: t.field({
        resolve: (parent) => parent.edges,
        type: [Edge],
      }),
      pageInfo: t.field({
        resolve: (parent) => parent.pageInfo,
        type: PageInfo,
      }),
    }),
  });

  return Connection;
};

const User = builder.objectType('User', {
  fields: (t) => ({
    username: t.field({
      type: 'String',
      resolve: (u) => u.username,
    }),
    password: t.field({
      type: 'String',
      resolve: (u) => u.password,
    }),
  }),
});

const UserConnection = buildConnectionType('User', User);

but I'm getting the following typescript error for the parent.node resolver:

Type 'T' is not assignable to type '[T] extends [readonly (infer Item)[] | null | undefined] ? ListResolveValue<T, Item, T> : MaybePromise<T>'.

I Don't really understand what I'm doing wrong so I was hoping someone could help me. Thanks :)

[jnssnmrcs]

Just to add: I just tested and it works without any issues if I just @ts-ignore the compiler error...

[hayes]

This is a side effect of some complicated types intended to make resolver errors more clear. It doesn't work well with genetics because the generic might be an array. It should be safe to ignore

[hayes]

Curious if there is a reason you are not using the relay plugin to implement this pattern?

[hayes]

I don't think there is any reason it wouldn't work with user ordering, you still have access to all the args (I found a few connections in our codebase that do this).

That being said, if you are using Prisma, the Prisma plugin will work much better for creating connections and makes things way simpler

[jnssnmrcs]

I think I'm tripping over my own thoughts here, and I also totally missed that the prisma plugin also supported generating connections....thanks again!

[jnssnmrcs]

Could you point me towards the places in the code base you do ordering together with the resolveCursorConnection as it is used above (by using where-clause with lt and gt) because I can't get it to work..

[hayes]

I don't think I have anything public for that specific use case (I meant the API I work on for work)

Basically what you need to do is use the before/after as normal (on whatever column the ordering is happening on). Then for the orderBy apply it as given by the user unless inverted is true, in which case you would invert the ordering the user requested.

This inversion is required to ensure that limits apply from the correct end of the range.

For Prisma I'd highly recommend the Prisma plugin. You can also just use the connection helper from the Prisma plugin.

The cursor helper is for cases where the db doesn't support cursors natively. Prisma actually has a cursor pagination API which might be cleaner to use (this is what the Prisma plugin does). But wouldn't work well with this helper.

This is what the Prisma plugin uses: https://github.com/hayes/pothos/blob/main/packages/plugin-prisma/src/util/cursors.ts#L319

[jnssnmrcs]

Thanks for explaining, i will check out the prisma plugin but i just wanted to understand how it would work for my own sanity :D really appreciate it!