Home / Questions / 480331
Accepted
Agustin G.
Asked: 2022-09-01 05:28:53 +0800 CST 2022-09-01 05:28:53 +0800 CST

Exclamation marks in graphQL definitions. How do I use them correctly?

  • 772

I have a question with graphQL (actually I have a lot because I just started using it, but this one is punctual)

Let's imagine that I declare a type, for example Usuarios.

type Usuario {
    username: String!
    password: String!
}

And then I have the queryUsuarios

Querys {
    getUsuarios: [Usuario]!
}

If I define this query that instead of returning {Users} , I destruct it and hide the password in this way

{ ...Users, password: null }

That's when all the questions come in.

The fact that I Usuariohave defined in the type password: String!makes the backend, when it wants to return the user created with the password to null, throw me an error saying that it cannot return null from a non-nullable property.

So, what is the correct way to say that a variable must be of a strict type, but at the same time be able to ''nullify'' it in case it is sensitive data?

On the other hand I don't quite understand the difference between returning [User], [User!], [User]! or [User!]!

From already thank you very much

graphql

1 Answers

  1. Best Answer

    I am also studying graphQL, I share my notes.

    You want to query a list of users with graphQL query language:

    Querys {
    getUsuarios: [Usuario]!
}

    The resolver Queryexpects a list type [User] with zero or more values , defined in the Object type Usuario.

    List Object Type with exclamation mark

    With the exclamation mark "!", it is specified that a list cannot receive a value of type null. If the list received this value, graphQLit would return the following message:

    "message": "Cannot return null for non-nullable field Query.getUsers."

    "data": null

    Here I want to make a point very clear:

    The getUsers query can return an empty list [] (zero or more values), but not a null type.

    List Object type without exclamation mark

    If the Query were defined without "!" in the list [Usuario]:

    Querys {
        getUsuarios: [Usuario]
    }

    When doing the query, assuming that the list [Usuario]for some reason comes as a type value null, graphQL would return the following message:

    "data": {
    "getUsuarios": null
  }

    Object type with exclamation mark

    If the Query were defined with double "!", one for the list [Usuario]and one for the type Usuario:

    Querys {
        getUsuarios: [Usuario!]!
    }

    It is specifying, for the type Usuario, that all the fields of each element of the list Usuariomust be included.

    For example, if the list Usuarioshad only one element Usuariowhere the field did not exist password, graphQL would return the following message:

    "message": "Cannot return null for non-nullable field User.password."

    And more importantly, the other elements of the list would be discarded , even if these had the field password, graphQL would return the following message:

     "data": null

    Object type without exclamation mark

    If the Query were defined without "!" in the type Usuario:

    Querys {
        getUsuarios: [Usuario]!
    }

    It is specifying that not all the fields of each element of the list Usuariomust be included.

    For example, if the list Usuarioshad only one element Usuariowhere the field did not exist password, graphQL would return the following message:

    "message": "Cannot return null for non-nullable field User.password."

    However, graphQL would return list items that have the field password.

    • 2