123456789_123456789_123456789_123456789_123456789_

GraphQL::Client::ImplicitlyFetchedFieldError

Similar to UnfetchedFieldError, but raised when trying to access a field on a GraphQL response type that happens to be fetched elsewhere by another fragment but not by the current fragment. The data is available, but isn't safe to rely on until it is explicitly added to the fragment.

This protection is similar to Relay's Data Masking feature.

Parent Data Leak

One source of these data leaks may come from a parent fragment fetching the data used down in a nested subview.

For instance, a controller may fetch a user and include its fullName.

UserQuery = Client.parse <<-'GRAPHQL'
  query {
    user(name: "Josh") {
      fullName
      #...Views::Users::Show::User
    }
  }
GRAPHQL

Many layers deep, a contact info helper might also too want to make use of the user's fullName.

UserFragment = Client.parse <<-'GRAPHQL'
  fragment on User {
    location
    # forgot fullName
  }
GRAPHQL

user = UserFragment.new(user)

# ok as `location` was explicitly queried
user.location

# raises UnfetchedFieldError, missing fullName field in query
user.full_name

In this case, the raw GraphQL will include both location and fullName:

{
  "user": {
    "fullName": "Joshua Peek",
    "location": "Chicago"
  }
}

If the controller for some reason decides its doesn't care about fullName anymore and stops querying it, it will break the helper. The developer just looking at that controller file isn't going to know some other helper on the other side of the codebase still cares about fullName.

Self contained functions should only safely rely on data dependencies they explicitly ask for. If both the controller and our helper explicitly state they both need fullName, that data will always be fetched even if the data requirements for one of the functions changes.

Child Data Leak

Similar to the parent data leak scenario, but occurs when a subview fetches data that our root view didn't explicitly ask for.

<%graphql
  fragment User on User {
    fullName
    location
  }
%>

UserQuery = Client.parse <<-'GRAPHQL'
  query {
    user(name: "Josh") {
      #...Views::Users::Show::User
    }
  }
GRAPHQL

user = UserQuery.new(data)

# raises UnfetchedFieldError, missing fullName field in query
user.full_name

The raw flattened data will include fullName just like the previous example. But again, we should depend on our UserQuery always having fullName available show the subview be modified.

See Also