Question

I’m a linq noob…. can someone please some me how to achieve this using linq… I’m trying to compare 2 lists in both directions…

    internal void UpdateUserTeams(int iUserID)
    {
        UserTeamCollection CurrentTeams = GetUserTeams(iUserID);
        UserTeamCollection UpdatedTeams = this;

        foreach (UserTeam ut in CurrentTeams)
        {
            if(!UpdatedTeams.ContainsTeam(ut.ID))
            {
                RemoveTeamFromDB();
            }
        }

        foreach (UserTeam ut in UpdatedTeams)
        {
            if (!CurrentTeams.ContainsTeam(ut.ID))
            {
                AddTeamToDB();
            }
        }

    }


    public bool ContainsTeam(int iTeamID)
    {
        return  this.Any(t => t.ID == iTeamID);
    }

Answer 1

So converting your initial question to an english requirement:

    foreach (UserTeam ut in CurrentTeams)           // for each current team
    {
        if(!UpdatedTeams.ContainsTeam(ut.ID))       // that is not in the updated teams list
        {
            RemoveTeamFromDB();         // remove it from the database
        }
    }

    foreach (UserTeam ut in UpdatedTeams)       //for each of the teams in the updated teams list
    {
        if (!CurrentTeams.ContainsTeam(ut.ID))  //if the current team does not contain the updated team
        {
            AddTeamToDB();              //add the team to the database
        }
    }

Therefore, you want to do:

//select all current teams that are not in updated teams list
CurrentTeam.Except(UpdatedTeams).All(team => { RemoveTeamFromDB(team); return true; });

//select all updated teams that are not in the current teams list
UpdatedTeam.Except(CurrentTeams).All(team => { AddTeamToDB(team); return true; });

Make sure your UserTeam object has proper overrides for the Equals and GetHashCode methods, so that comparison between two UserTeams is accurate 🙂