Optimize loading of data in the GraphQL API to avoid multiple loadings of the same item.

Summary of data loading

For the following query:

{
  content {
    blogPosts {
      title
      body { html5 }
    }
  }
}

data loading goes that way:

• the blog post content items are loaded using `ContentService::findContentInfo()`
• for each requested field (title, body), the content item is loaded using contentService::loadContent(), and the field's value is returned.

This results in an n*m complexity, with n the number of content items and m the number of requested fields.

Options

In-memory caching

Add a data-loader layer that is always used to load items, and have it cache each loaded item in memory, and return that item when it gets loaded.

Pro

• Generalizing a data-loader matches the GraphQL server implementation standards

Cons

• It adds an extra layer

Load content instead of content info

If instead of findContentInfo() we use findContent(), the underlying fields would receive the full `Content` item, and wouldn't have to fetch it again.

Pros

• doesn't require an extra layer

Cons

• doesn't separate the data loading logic from the resolvers
• might not always be applicable as it is limited to loading content (content type already has its own in-memory cache)