Question

How can I basically carry out a unique constraint on a string data-type field.

class User{
  String username
  String Email

  static hasMany = [roles:Roles]

     static constraints = {
     Email(email:true)
     username(unique:true)

    }
}

Is there any simple way to implement username(unique: true)

Or must I manually check the database using methods like .findByNameLike?

The username should be unique, but the uniqueness is should be case-insensitive.

Answer 1

So, if you want to have unique and case insensitive usernames, there are two possible approaches.

The simple one:

• Store them upper or lower case and use the unique constraint.

or, regarding performance, more expensive:

• Store them in mixed case and use a custom validator, which checks the database by comparing given and existing usernames case insensitive.

Now it depends, if you just want to give the user the freedom to enter his username in the case he wants (first possibility) or you want to keep the usernames case for displaying reasons (second possibility).

Your question sounds like the second one, so a custom validator would look like this:

class User { 
  String username 
  String email

  static hasMany = [roles:Roles]
  static constraints = {
    email(email:true)
    username(validator: {
              return !User.findByUsernameILike(it)
            })
  }
}

Hope that helps.

[Edit]

As Heinrich states in his comment, the validator above will cause problems when users are able to change their username.

Quick & dirty, but I think this solves the issue:

username(validator: { val, obj ->
                      def similarUser = User.findByUsernameILike(val) 
                      return !similarUser || obj.id == similarUser.id
                    })

Beware, it’s not tested and I’m not sure if you’re able to define variables in validators.

Meta: I would never let the users change their username 😉