Check uniqueness

[nichoth]

A simple usecase — be sure that documents are unique, indexed by a given field.

Intuitively, I try this:

const query = fql`
    let theUser = User.by_name(${userData.username}).first()
    
    if (theUser.exists()) {
        abort("Username exists already.")
    } else {
        User.create({
            username: ${userData.username},
            password: ${hashValue}
        })
    }
`

But I get an error response,

error: Type Null is not a subtype of Boolean

That is exactly what I want to check for — null or does it exist.

I have tried searching across the docs and forums; a problem is that search queries return results from the previous version of Fauna query language.

[wallslide]

I believe this link explains your issue:

Executing `Collection.firstWhere().exists()` should return `true` or `false`

exists() does return true or false. But the return type of first() and firstWhere is a YourDocumentType | Null [image] The exists method only exists on Documents and “NullDocs”. exists() is used to check if a reference is in the database. A NullDoc are like a a pointer we know points at nothing because either it doesn’t exist or you don’t have permission to it. When you use .byId that method either returns a document or NullDoc, [image] A NullDoc is like a bad reference, but it has informa…

Basically, you could use either of these

let alreadyExists = theUser != null

or

let isUnique = User.by_name(${userData.username}).isEmpty()