"Demystifying Cache Normalization" blog article seems to be wrong

This article from apollographql.com says:

For example, if we were to:

1. Perform a GetAllTodos query, normalizing and caching all todos from a backend
2. Call GetTodoById on a todo that we had already retrieved with GetAllTodos

… then Apollo Client could just reach into the cache and get the object directly without making another request.

I tested this and GetTodoById did NOT retrieve the todos from the Apollo Cache.

Intended outcome:

The official blog post accurately documents the behavior of Apollo Client.

Actual outcome:

The official blog post does NOT accurately document the behavior of Apollo Client.

I created a project to show this: https://github.com/srmagura/how-does-apollo-work. It is a trivial GraphQL API server and a React client which calls the server. The client first calls getAllTodos which returns 5 todos. When you click the button, the client calls getTodoById for each todo. Each GraphQL request for getTodoById results in a network call. This contradicts what the blog post says should happen.

For what it’s worth, I think Apollo Client is behaving correctly and the blog post is just wrong.

How to reproduce the issue: Clone and run the repository I linked to in the previous section.

Versions

  System:
    OS: macOS 12.5.1
  Binaries:
    Node: 16.16.0 - ~/.nvm/versions/node/v16.16.0/bin/node
    Yarn: 1.22.19 - ~/.nvm/versions/node/v16.16.0/bin/yarn
    npm: 8.16.0 - ~/.nvm/versions/node/v16.16.0/bin/npm
  Browsers:
    Chrome: 105.0.5195.102
    Firefox: 104.0.1
    Safari: 15.6.1

Additional reference StackOverflow answer that backs up what I said: https://stackoverflow.com/a/50839798/752601

[dylanwulf]

This is mentioned in the stackoverflow link in the issue description, but for anyone who finds this thread looking for a solution: this functionality does exist in apollo client, it just needs a little bit of manual setup. You can find instructions here: Cache Redirects. (This is not mentioned in the article, so I agree that the article should be changed)

[srmagura]

@markusgabriel Apollo cannot know the true behavior of your GraphQL server (i.e. resolvers). So Apollo cannot assume getTodoById(id: "123") returns the todo with ID=“123”. Therefore, Apollo must make the network call — it cannot simply look up the Todo in the cache.

If it helps, imagine you had a query like getAllTodosExcept(id: "123"). You would be upset if Apollo used the cache and returned the Todo with ID=“123” in this case!