I'm at a bit of a loss here.
I have a one-to-many relationship between Project and Task and another between Task and TaskEvent.
A Task only exists in the context of a Project and once assigned to a Project can't be changed to belong to another Project.
A business rule states that a Task can only be deleted, and therefore removed from the collection of Tasks that belong to a certain project, if the Task has no TaskEvents captured against it.
How do I specify this in Entity Framework? I'm using Self-Tracking entities, but actually I'm at a loss as to where to define this kind of rule in general. We have other rules that are db ignorant, but how does one define a business rule, preferably that exists in isolation from the entity classes as they are regenerated, as a class of their own with a single responsibility?
I'm thinking I'll have to implement some sort of validator that can use reflection to pick up these 'rule' classes based on the type of the object being validated and then have them each perform their validations.
But how do I push the object context into that? Should my validator have an instance of the object context and then pass it through to each rule as it is executed?
And even more flustering, how do I detect the deletes? Will I have to call up the old version of the Project and do a comparison of it's old tasks and current tasks and then check all the deleted ones to make sure they have not TimeEvents captured?
What are the drawbacks to this method and what else can you suggest?
EDIT: I should specify that we're using an n-tier design and both the client apps(MVC and Silverlight) hit WCF services to do anything useful. This is obviously the layer we want to implement the validation in, although if we could use those rules that aren't db specific on the clients that would be great. We're using DataAnnotations for those validations at present.
Thanks