Question

Any suggestions on clean ways to solve this design issue?

public class Task
{
    public User Assignee
    public User Assigner
}

public class User
{
    public string Name
}

So a task has two users. But now we want to add support for groups…

public class Group
{
    public string Name
    public IEnumberable<User> Users
}

And we want the task to be able to handle a group as an Assignee

public class Task
{
    public User/Group Assignee
    public User Assigner
}

When I think about inheritance here. Group “is a type of” User doesn’t meet this LSP because Group “is not replaceable by” User

I’m using Entity Framework (model first).

Answer 1

Group is not User. That is incorrect modelling. If you need inheritance define a new top level abstract entity – for example Identity and derive User and Group from this entity:

public class Task
{
    public Identity Assignee
    public User Assigner
}