Graphql scalar type for a value that can be string or object? - graphql

Question

i have an api for sign up which returns error of string or null,
error: 'Email already use' or error: null
how do i construct it in schema? what i have now is this:
const typeDefs = gql`
type Mutation {
signUp(email: String, password: String): String
}
`;
since typeof null is object, how can i make it like this in graphql?
signUp(email: String, password: String): String || Object
Help?

Answer 1

GraphQL has a standard syntax for returning error values and your schema does not directly need to account for this.
In your schema I would “unconditionally” return whatever type you’d normally expect to return:
type UserAccount { ... }
type Query {
me: UserAccount # or null if not signed in
}
type Mutation {
signUp(email: String!, password: String!): UserAccount!
}
If it’s unsuccessful, you will get back a null field value (even though the schema in theory claims it shouldn’t) and an error.
{
"errors": [
{
"message": "It didn’t work",
"locations": [ { "line": 2, "column": 3 } ],
"path": [ "signUp" ]
}
]
}

Answer 2

In GraphQL you can define what field can be null and what can't.
Take a look at the docs:
https://graphql.org/learn/schema/#object-types-and-fields
String is one of the built-in scalar types - these are types that
resolve to a single scalar object, and can't have sub-selections in
the query. We'll go over scalar types more later.
String! means that the field is non-nullable, meaning that the GraphQL service promises
to always give you a value when you query this field. In the type
language, we'll represent those with an exclamation mark.
So in case of your schema String is absolutely fine. It can be null
type Mutation {
signUp(email: String, password: String): String
}