I wonder how I can validate an entity in its prope...

# announcements

[ecampolo]

I wonder how I can validate an entity in its properties both via constructor and setter without duplicating code. More formally, how do you get around with aggregate invariants (DDD). For example:

class Person(email: String) {
    var email: String = email
    set(value) {
        require(value.trim().isNotEmpty(), { "The email cannot be blank" })
        field = value
    }

    init {
        require(email.trim().isNotEmpty(), { "The email cannot be blank" })
    }
}

I tried with Delegation but feels a little bit complex since I would need to have NotEmptyString , NotEmptyCollection, or any kind of validation. Also I want to avoid those extra objects per property.

[Andreas Sinz]

class Person(_email: String) {
    var email: String = email
    set(value) {
        require(value.trim().isNotEmpty(), { "The email cannot be blank" })
        field = value
    }

    init {
        email = _email
    }
}

Just assign the value of the constructor-argument to your email-property?

[ecampolo]

do you mean?:

class Person(email: String) {
    var email: String = email
        set(value) {
            require(value.trim().isNotEmpty(), { "The email cannot be blank" })
            field = value
        }

    init {
        this.email = email
    }
}

[Andreas Sinz]

yeah

[ecampolo]

haha i tried so many variants that I cannot tell what was the issue with that .. but, it seems like it is want I want., i ll try it to see if I am missing something., thank you Andreas 😉

[ecampolo]

dont I reassigning the variable twice ?

[ecampolo]

i think thats the issue

[ecampolo]

if I do

Person(email = "")

, the object is first initialized with an empty value and then executing the init block calling the setter, resulting in an exception

[Andreas Sinz]

yeah, thats unfortunate, but you won't be able to get a vaild instance nevertheless

[ecampolo]

true, but it feels ... dirty ?

[Andreas Sinz]

indeed

[Andreas Sinz]

is it necessary that email is mutable?

[ecampolo]

no, but it is an example, assume that it is., like having an age field whose value should be positive

[ecampolo]

maybe an Employee class with role, job, area, etc

[ecampolo]

the underlying problem is how to deal with validation both while constructing the object and then, if a need to update one of its values