How do I add a constraint for a list to not be empty in smithy?

Question

How do I add a constraint for a list to not be empty in smithy? I have a smithy list as below -

list CarsList {
    member: Car
}

struct Car {
    @required
    Name: CarName
}

@length(min: 1)
string CarName

I want to add a constraint/trait to the list CarList to not allow it to be empty.

I tried to add @required to CarName in struct Car and @length(min: 1) to string Carname as shown above but it did not do any work.

Answer 1

You can use the @min trait for such requirements.

list CarsList {
    @min(1)
    member: Car
}

struct Car {
    @required
    Name: CarName
}

@length(min: 1)
string CarName

If you create an instance of CarsList with no elements, it will be considered invalid. @min trait specifies a minimum amount of elements that the list must have, here we have at least 1 is required.