Nullability Guard

Nullability Guard

This plugin helps us guard against non-null values crashing our queries in production. It does this by defining that every scalar value have a "fallback" value defined, so if we see a nullish value on an otherwise non-null field, we will fallback to this instead of crashing the query.

The nullabilityGuardPlugin by default only guards when process.env.NODE_ENV === 'production'. This is intended so you see/catch these errors in development and do not use it except as a last resort. If you want to change this, set the shouldGuard config option.

1import { nullabilityGuardPlugin } from 'nexus'
2
3const guardPlugin = nullabilityGuardPlugin({
4  onGuarded({ ctx, info }) {
5    // This could report to a service like Sentry, or log internally - up to you!
6    console.error(
7      `Error: Saw a null value for non-null field ${info.parentType.name}.${info.fieldName} ${
8        root ? `(${root.id || root._id})` : ''
9      }`
10    )
11  },
12  // A map of `typeNames` to the values we want to replace with if a "null" value
13  // is seen in a position it shouldn't be. These can also be provided as a config property
14  // for the `objectType` / `enumType` definition, as seen below.
15  fallbackValues: {
16    Int: () => 0,
17    String: () => '',
18    ID: ({ info }) => `${info.parentType.name}:N/A`,
19    Boolean: () => false,
20    Float: () => 0,
21  },
22})

Null Guard Algorithm

• If a field is nullable:
  • If the field is non-list, do not guard
  • If the field is a list, and none of the list members are nullable, do not guard
• If the field is non-nullable and the value is null:
  • If the field is a list:
    • If the value is nullish, return an empty list []
    • If the list is non-empty, iterate and complete with a valid non-null fallback
  • If the value is a Union/Interface
    • Return with an object with the __typename of the first type which implements this contract
  • If the field is an object:
    • If the value is nullish
      • If there is a fallback defined on the object for that type, return with that
      • Else return with an empty object
    • Return the value and push forward to the next resolvers