7. Local updates

What if you need to update a query data locally, without making any request? You don't control reducer responsible for data updates after all. Fortunately, there is a way - local updates.

You can define them in the similar way to normal mutations:

const deleteBookLocally = id => ({
  type: DELETE_BOOK_LOCALLY,
  meta: {
    mutations: {
      FETCH_BOOK_DETAIL: {
        updateData: data => (data.id === id ? null : data),
        local: true,
      },
    },
  },
});

As you can see, it looks similar to normal mutations. One difference is that there is no request key - after all we didn't want to make any request. Another difference is that the update function is not attached directly to the query type (in our case FETCH_BOOK_DETAIL), but inside the object as updateData. This is because we need to pass also local: true to the mutation to mark it as a local one.