This is similar to the login system described in the blog post:
q := fmt.Sprintf(`
{
login_attempt(func: eq(email, %q)) {
checkpwd(pass, %q)
}
}
`, email, pass)
resp, err := txn.Query(ctx, q)
In this example, we check that the email is unique, by using a hash index on email attribute.
That’s the benefit of transactions, such checks are possible completely via client code. If you have multiple people writing to Dgraph, they should all be running this logic transactionally.
I now reckon this is the same response as by @calummoore.