Query with errorPolicy "all" cannot use onError, onCompleted effectively

Hi 👋 ! A team of us are working on transitioning a production application to Apollo with use of hooks in React. We have the following use case:

• use a query with errorPolicy set to “all” (so that error and data may both have value)
• use onError, onCompleted attributes to perform some side effects

Intended outcome:

I’d expect to be able to perform “completed” and “errored” functionality if the errorPolicy=“all”, since this would be a congruent outcome of the data, error, loading pattern commonly used when both data and error may be populated with this error policy.

Actual outcome:

If there is a partial error from one of the fields, only onError called (since I’ve defined both). I think issue can be found in this either/or method (here in react-apollo, or here in apollographql/apollo-client).

I wonder: could onError receive data as a 2nd ordinal argument in the event that there is both an error and data?

How to reproduce the issue:

I’ve reproduced here: https://codesandbox.io/s/inspiring-surf-pcrgj?file=/src/App.js

Here’s an inline example:

import {useQuery} from '@apollo/react-hooks`
import gql from 'graphql-tag'

const someSideEffect = (error, data) => {
if (!data) console.error(error)
 else if (data && error) {
  console.info(error)
  alert(`some of the data is shiny: ${data.isShiny}`)
 } else {
   console.log('no error 🙌')
 }
}

const QUERY = gql `
query get_stuff {
 stuff {
  isShiny
  someFinnickyFieldThatErrorsOutSometimes
 }
}
`

function Stuff() {
 const {data, loading} = useQuery(QUERY, {
  errorPolicy: 'all',
  onCompleted: (data) => someSideEffect(null, data),
  onError: (error) => someSideEffect(error),
 });

 if (loading) return 'loading...'
 if (!loading && data) return <div>{JSON.stringify(data, null, 4)}</div>;
}

Solution Proposal

Possible solution 1: provide data as a 2nd ordinal argument to onError

const {data, loading} = useQuery(QUERY, {
 errorPolicy: 'all',
 onCompleted: (data) => someSideEffect(null, data),
 // Perhaps It'd be SO nice if onError had access to data ❤, but it does not 💔
 onError: (error, data) => someSideEffect(error, data),
});

One might also argue additionally (or alternatively) that error in the onCompleted callback should be made available. Hence, in the case of errorPolicy=“all” this dichotomy between “completed” and “errored” is somewhat difficult to discern. Hence:

Possible Solution 2: Perhaps if developer does not define onError and errorPolicy is “all”, then onCompleted is always called with both data and error?

Possible Solution 3: Alternatively, and more generally it should just always call “onCompleted” with access to both error and data when both are defined (errorPolicy=“all”). And we remove the notion of onError entirely?**

In summary, there are many solutions to this perceived bug, and the API seems unclear for this use case. These three solution proposals above are ranked in order from least to most invasive.

Version

@apollo/react-components@3.1.5

System:
OS: macOS Mojave 10.14.6
Binaries:
Node: 12.16.1 - ~/.volta/tools/image/node/12.16.1/6.13.4/bin/node
npm: 6.13.4 - ~/.volta/tools/image/node/12.16.1/6.13.4/bin/npm
Browsers:
Chrome: 83.0.4103.116
Edge: 83.0.478.61
Firefox: 76.0
Safari: 13.0.4

(FYI originally reported here, moving) https://github.com/apollographql/react-apollo/issues/403

[zorji]

I am testing with apollo/client@3.4.1, I got a completely different result. When errorPolicy=all, it does not trigger onError on partial failure.

I can’t find the official explanation on the website, when errorPolicy=all and when there is a partial error, should it trigger onError?

I found this PR https://github.com/apollographql/apollo-client/issues/6492 and it looks like it was not expected on trigger onError.

Relevant issue for me in vue-apollo https://github.com/vuejs/vue-apollo/pull/1225/files#r679619257

[llamadeus]

I’m currently having some troubles when setting errorPolicy: 'all' because the onCompleted callback is being called even if data is null. This will result in null being passed for the data argument but the function signature does not reflect this circumstance.

I’m using "@apollo/client": "^3.2.7".