Craft GraphQL APIs in Elixir with Absinthe

Marking Arguments as Non-Null

In the last section, you saw variable declarations that featured use of exclamation marks to ensure variable values were provided. It looked something like this:

query ($filter: MenuItemFilter!) {
  menuItems(filter: $filter) {
    name
  }
}

The document here declares that the $filter variable is a MenuItemFilter, while the addition of an exclamation mark denotes that a value is mandatory. This is a constraint that the document designer (usually a front-end developer) builds into the query, but the schema designer can enforce non-null constraints on the backend as well.

Let’s say, for instance, that we wanted to ensure that a filter was always provided to the :menu_items field, regardless of what the ...