Add generic types for updates

[lukasluecke]

I have the following code (in updates.Mutation) to update a list count after creating an item:

createItem: (result, args, cache, info) => {
    cache.updateQuery({query: ListDocument, variables: {parentId: args.input.parent}}, data => {
        data.parent.items.totalCount = data.parent.items.totalCount + 1;
        return data;
    })
}

---

There's currently no validation / hints on variables or data, which should be possible by passing the respective types as generics to updateQuery (similar to how useQuery/useMutation hooks work).

I also get a typescript error on data.parent.items:

Property items does not exist on type DataField

---

It would also be great to have the possibility to type the whole function createItem, so we could have validation / hints on args and result as well.

Right now I get another typescript error on args.input.parent:

Property parent does not exist on type string | number | boolean | Variables | ScalarObject | Scalar[] | Variables[]

[jBugman]

Was meant to post almost exactly that.
As a workaround I currently use this pattern, @lukasluecke:

const post = data.addPost as Post;
...
return {
      ...prevData,
      post,
    } as Data;

[lukasluecke]

@jBugman Thanks for the workaround, that works (and is nicer than just @ts-ignore 😅).

[JoviDeCroock]

We could add a generic here: https://github.com/FormidableLabs/urql-exchange-graphcache/blob/master/src/types.ts#L69

Not entirely sure if that could solve all use cases but I'll dig into that later.

[lukasluecke]

@JoviDeCroock Looks like that could solve the issues, thank you. 🙏

[JoviDeCroock]

Hmm thinking about it further, TS won't allow it being set there. Will have to dig deeper into this. Sorry about that hadn't given it enough thought yet

[lukasluecke]

No problem, it's not a blocking issue, but I think this would be a great addition 🙂