Feature request: hooks for data fetch

[Jean-Baptiste AUBRÉE]

Hi @logaretm,

First of all, this library is great job.

Clear and concise description of the problem

When we use fetching APIs like fetch, axios or villus, we need almost all the time to work with data, specially setting mapping response data.
Currently, the only solution i found to do that with villus is using watcher and i find this not optimize:

const { data, isDone } = useQuery({
  query: myQuery,
  variables: ...
})
watch(isDone, (value), {
  if (value && data.value)
    mapAndSetMyData(data.value)
})

Suggested solution

Add hooks like onSuccess, onError like this is setup on Apollo

I think this is a small feature that will help a lot.
What do you think about it ?

[Jean-Baptiste AUBRÉE]

Oh, i didn't see then function was provided, this is a solution. Feel free to close this issue if you think onSuccess and onError is too much for this library but i think it's important to have a specific hooks for error and success

[Jean-Baptiste AUBRÉE]

Update: onFulfilled function in then is only triggered on first call so it does not work with computed variables etc...

[Jean-Baptiste AUBRÉE]

@logaretm Do you think we can do the same thing for mutations ?

[Abdelrahman Awad]

@jbaubree Usually mutations are executed explicitly, so I don't think it is as common as queries but I don't see the harm. Feel free to PR it, and I guess you ran into needing it recently, would love to hear about it as well, use-case wise.

[Jean-Baptiste AUBRÉE]

@logaretm There are several reasons why I think it is necessary.
Let's take a simple example:
We are in a login page.

const { execute: signIn } = useMutation<{ signIn: { token: string } }>(SIGN_IN)

async function onSubmit() {
  signIn({ publicAddress, signature }).then(({data, error}) => {
    if (data) <-- Here we don't know if mutation is a success and i find data/error conditions are pains
      //...
    if (error)
      //...
  }
}

Second reason, i find code more readable like this:

const { execute: signIn } = useMutation<{ signIn: { token: string } }>(SIGN_IN, {
  onData(data) {
    setToken(data.signIn.token) <--- We are sure that data exists here
    router.push({ name: 'Root' })
  },
  onError(err) {
    ...
  },
})

async function onSubmit() {
  signIn({ publicAddress, signature })
}

If you confirm that you are ok with that, i will PR it when i will get some free time