Problem:

We want a user to have one of two possible roles: BASIC or PREMIUM.

Currently, a client could potentially set the role of the user to any arbitrary string, like CHICKEN, which would obviously not make sense in our app.

We need a mechanism to establish a contract that the user.role can only be set to a pre-approved value.

Solution:

Enums

Enums are a way to create a list of pre-approved values for a certain type. In our case, we want to define an enum named Role that contains two possible values: BASIC and PREMIUM.

This mechanism tells our program that a Role type can only ever have the value BASIC or PREMIUM.

Implementation:

How to use enums to improve our role-based permission system

Step 1

Define the Role enum in the top level of the schema.

Step 2

Specify the Role enum as the return type for the role field on the User type (in schema/user.js).

Step 3

Use the Role enum as the argument type for our updateRole mutation:

This has the added benefit of giving us autocomplete in GraphQL Playground when setting the user’s role with this mutation:

Sweet! Less room for error.