Remove an specific user from Room in EF Core-CodePudding

I have a room including some users. I want to remove an specific user from the room.

Here are my Models:

public class RoomModel
{
    [Required]
    public int Id { get; set; }
    public string Name { get; set; }
    public string Admin { get; set; }
    public ICollection<UserModel> Users { get; set; }
}

public class UserModel
{
    [Key]
    public string UserID { get; set; }
    public string UserName { get; set; }
}

And my database context:

 public class DBContext :  IdentityDbContext
    {

        public DBContext() 
        {

        }

        public DBContext(DbContextOptions<DBContext> options) : base(options)
        {

        }

        public DbSet<RoomModel> Rooms { get; set; }
        public DbSet<UserModel> Users { get; set; }
 }

How can I remove an specific user from the room and save changes in database?

CodePudding user response：

Load rooms with navigation property Users, then find the user to remove.

 var userId = "1234-ABC";

 // Eager loading
 var rooms = db.Rooms
               .Include(u => u.Users)
               .ToList();
 // or Explicit loading
 // var rooms = db.Rooms.Collection(u => u.Users).Load();

 var user = rooms.Users.Where(u => u.UserId == userId).FirstOrDefault();
 rooms.Users.Remove(user);  // should check if user is not null
 // now you can save changes to db
 db.SaveChanges();

CodePudding user response：

Since in your UserModel enity there is no CLR property which holds the foreign key for the relationship, a shadow property RoomModelId is created.

See the documentation for more information: Shadow and Indexer Properties.

We can use this shadow property to efficiently perform the deletion without making unnecessary queries to the database.

// We get the room somehow.
var room = db.Rooms.First(r => r.Name == "room A");

// Create a user with the desired id.
var user = new UserModel { UserID = "x" };
// Or we get a user from the database. But this is an unnecessary query.
//var user = db.Users.First(u => u.UserID == "x");

// Set the foreign key value to the shadow property.
db.Entry(user).Property("RoomModelId").CurrentValue = room.Id;

// Mark entity as deleted.
db.Entry(user).State = EntityState.Deleted;

db.SaveChanges();

I would add the following properties to the UserModel, for more convenience:

public int RoomModelId { get; set; }
public RoomModel Room { get; set; }