Question

Here’s the model I have.

public class Notification
{
    public int NotificationID { get; set; }
    public bool ReadStatus { get; set; }
    public DateTime DateCreated { get; set; }
    [ForeignKey("User"), Column(Order=0)]
    public int UserID { get; set; }
    [ForeignKey("Actor"), Column(Order = 1)]
    public int ActorID { get; set; }

    [ForeignKey("NotificationType")]
    public int NotificationTypeID { get; set; }
    //public int ObjectID { get; set; }
    [ForeignKey("Comment")]
    public int? CommentID { get; set; }
    [ForeignKey("Project")]
    public int? ProjectID { get; set; }
    [ForeignKey("Book")]
    public int? BookID { get; set; }

    public Comment Comment { get; set; }
    public Book Book { get; set; }
    public Project Project { get; set; }
    public NotificationType NotificationType { get; set; }
    public User User { get; set; }
    public User Actor { get; set; }
}

Any given row will only have ONE of the following: BookID, ProjectID, CommentID
I want to get a count of total notifications BUT I have to group them by NotificationType AND one of the those three IDs, the other two IDs are null. There may be 10 comment notifications, but 5 of those are for a reply, and 5 are for another action – that should only be TWO notifications though, not 10.

How would I write a lambda expression to get these counts?

Answer 1

The following will work.

 var notificationCount = db.Notifications
      .GroupBy(x => new { x.CommentID, x.ProjectID, x.BookID, x.NotificationTypeID })
      .Count();

Based on This Answer