Automatic cache updates do not work in react apollo - reactjs

Question

The document says the cache can be automatically updated in the following example:
{
post(id: '5') {
id
score
}
}
mutation {
upvotePost(id: '5') {
id
score
}
}
Would the automatic update work in the following case when the cached object is in a list ? Like this:
This is a query that fetches a list of reviews:
{
reviewList(model:12){
list{
reviewId
text
}
cursor
}
}
When I update one of the reviews from the list to the server, react apollo does not automatically update the cached review:
mutation{
updateReview(reviewId:'1',text:'new text'){
reviewId
text
}
}
Is it a must to use update properties of the mutation component to update the cache?

Answer 1

Assuming you're using apollo-cache-inmemory, unless you are adding an item to or removing an item from the list, it shouldn't be necessary to use update. However, it's important to keep in mind that the cached data is normalized, and that Apollo utilizes the __typename and id (or _id) field to generate the cache key for any queried object. From the docs:
The InMemoryCache normalizes your data before saving it to the store
by splitting the result into individual objects, creating a unique
identifier for each object, and storing those objects in a flattened
data structure. By default, InMemoryCache will attempt to use the
commonly found primary keys of id and _id for the unique identifier if
they exist along with __typename on an object.
If the id field is missing, Apollo won't know how to match up the data from your query and the data from your mutation:
If id and _id are not specified, or if __typename is not specified,
InMemoryCache will fall back to the path to the object in the query,
such as ROOT_QUERY.allPeople.0 for the first record returned on the
allPeople root query. That would make data for given type scoped for
allPeople query and other queries would have to fetch their own
separate objects.
Fortunately, there's a workaround. You can of course just rename reviewId to id on the server side. However, if you want the cache to just use the reviewId field, you can pass in a dataIdFromObject function to your InMemoryCache constructor:
import { InMemoryCache, defaultDataIdFromObject } from 'apollo-cache-inmemory'
const cache = new InMemoryCache({
dataIdFromObject: object => {
switch (object.__typename) {
case 'Review': return object.reviewId
default: return defaultDataIdFromObject(object)
}
}
})
As long as resulting value is unique, you can utilize any other field (or combination of fields) in a similar fashion.