API

useMutation has an update function, whose purpose is to modify your cached data to match the modifications that a mutation makes to your back-end data

• this method allows us to interact with the cache as if we were interacting with a graphql API.
  • ex. we can make general queries, as well as use fragments to help
• we can interact directly with the cache with readQuery, writeQuery, readFragment, writeFragment, which are methods on the ApolloClient class
• we can get the cached version of an entity with cache.identify
  • an input { id: 1, title: '', mediaItems: [{...}] } gives us Nugget:1

Apollo cache object

• Here, queries mirror what our gql queries would look like to target the same data from a Graphql server. Therefore, it must be a complete and valid query.
• fragments on the other hand provide more random access (as opposed to sequential access) to our cached data.
  • therefore, we need to provide the cacheId as an argument to the fragment methods.

readQuery

• like a regular graphql query, only it is performed on the cache, rather than the GraphQL API

writeQuery

• uses the same shape as readQuery, but requires us to include a data option with the modifications we wish to make
• the shape of our query is not enforced, and we can write fields that aren't present in our Graphql schema.
• docs

readFragment

If the object in the cache is missing fields that exist on the fragment, then we will be returned null.

writeFragment

Just like readFragment, but like writeQuery, it requires a data object with the fields that we are writing.

updateQuery / updateFragment

Allows us to read and write cached data in a single method call.

• ApolloClient 3.5 and later
• docs

cache.modify

• docs

modify is a method we can execute on our cache that lets us modify individual fields directly

• differs from writeQuery and writeFragment in that it will circumvent any merge function we have defined, meaning that fields are always overwritten with exactly the values you specify.
• cannot write fields that do not already exist on the object in the cache.

cache.identify

Returns the cacheId for the specified object

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Backlinks

• Apollo Client Cache