NAME

Class::Workflow::Transition::Validate - Provide a hook for validating a transition (conditionals, input validators, etc).

SYNOPSIS

        package MyTransition;
        use Moose;
        with qw/
                Class::Workflow::Transition
                Class::Workflow::Transition::Validate
        /;
        sub validate {
                my ( $self, $instance, %args ) = @_;
                die "only the owner can apply this transition"
                        unless $args{user} eq $instance->owner;
        }

DESCRIPTION

This role will call the "validate" method at the appropriate time.

"validate" receives the same arguments as "apply", and is expected to die if any of the parameters for the transition are invalid.

Technically, this role doesn't do much more than adding syntactic sugar for "before 'apply'". However, it's value is in the convention that you can call "validate" without applying the body. This eases writing side effect free introspection of transitions.