Apollo pagination and cache-and-network fetch policy

Question

The apollo docs suggest a way to implement the merge function in a field policy when implementing pagination logic.

merge(existing = [], incoming) {
  return [...existing, ...incoming];
}

However, when I use 'cache-and-network' fetch policy for the query, that means that first it loads data from the cache, then it goes out to the network, and will append the existing list with the incoming data, so every item will exist in the cache twice, if the incoming data is the same as what was in the cache before.

What is the correct way to solve this? Can I differentiate between an initial load and a fetchmore request in the merge function? The merge function should obviously work differently for an initial fetch that should overwrite what we have loaded from the cache, and for a pagination fetch more.

Answer 1

In case anyone stumbled into this issue, solution as of Apollo 3 is:

fetchPolicy: 'cache-and-network',
nextFetchPolicy: 'cache-first',