Asp.net core Entity Framework 6 error with multiple key entity

Question

Hello I'm making a web app for events in my city (university homework)

I don't know why but I'm not getting what I want with EF. An event has schedules, and a user can join one shedule and rate it. I don't know why but my model doesn't work (count users in a schedule with users returns 0) also in the table dbo.UserJoinSchedule there is a column of type date... what I am doing wrong?

public class UserJoinEvent{
    public virtual int Id { get; set; }

    public virtual int EventId { get; set; }
    public virtual Event Event { get; set; }

    [Required]
    public virtual string ApplicationUserId { get; set; }
    public virtual ApplicationUser ApplicationUser { get; set; }

    public virtual int ScheduleId { get; set; }
    public virtual Schedule Schedule { get; set; }

    [Range( 0, DomainConstraints.VoteMax )]
    public virtual int? Vote { get; set; }
    [MaxLength(DomainConstraints.ReviewMaxLen)]
    public virtual string Review { get; set; }
}

 public class Schedule{
    public virtual int Id { get; set; }

    [DataType(DataType.DateTime)]
    public virtual DateTime DateTime { get; set; }

    public virtual int EventId { get; set; }
    public virtual Event Event { get; set; }

    public virtual ICollection<UserJoinEvent> UserJoined { get; set; }
}

public class Event{
    public virtual int Id { get; set; }
    [Required, MinLength(DomainConstraints.EventNameMinLen)]
    public virtual string Name { get; set; }

    [Required]
    public virtual string Description { get; set; }

    [Required]
    public virtual string ApplicationUserId { get; set; }
    public virtual ApplicationUser ApplicationUser { get; set; }

    public virtual double Latitude { get; set; }
    public virtual double Longitude { get; set; }

    public virtual ICollection< Schedule > Schedule { get; set; }

    public virtual int EventTypeId { get; set; }
    public virtual EventType EventType { get; set; }

    public virtual ICollection< UserJoinEvent > UserJoined { get; set; }
}

protected override void OnModelCreating(ModelBuilder builder){
        base.OnModelCreating(builder);

        builder.Entity< Event >( e => e.HasMany( o => o.Schedule ).WithOne( o => o.Event ) );
        builder.Entity< Event >( e => e.HasMany( o => o.UserJoined ).WithOne( o => o.Event ).OnDelete(DeleteBehavior.Restrict) );

        builder.Entity< EventType >( e => e.HasMany( o => o.Events ).WithOne( o => o.EventType ) );

        builder.Entity< Schedule >( e => e.HasKey( o => new {o.EventId, o.DateTime} ) );
        builder.Entity< Schedule >( e => e.HasMany( o => o.UserJoined ).WithOne( o => o.Schedule ).OnDelete(DeleteBehavior.Restrict));

        builder.Entity< UserJoinEvent >( e => e.HasKey( o => new {o.EventId, o.ApplicationUserId} ) );

        builder.Entity< ApplicationUser >( e => e.HasMany( o => o.UserJoined ).WithOne( o => o.ApplicationUser ).OnDelete(DeleteBehavior.Restrict));
    }

public enum Role { User, Mod, Admin }

public class ApplicationUser : IdentityUser{
    public virtual Role Role { get; set; }

    public virtual ICollection<UserJoinEvent> UserJoined { get; set; }
}

Query:

var @event = await _context.Events.Include( e => e.ApplicationUser ).Include( e => e.EventType ).Include( e => e.Schedule ).ThenInclude( uj => uj.UserJoined )
            .Include( e => e.UserJoined )
            .SingleOrDefaultAsync(m => m.Id == id);

View:

@foreach( var s in Model.Schedule ) {
                <div class="row">
                    <div class="col-md-5">@s.DateTime</div>
                    <div class="col-md-5"><b>Partecipanti:</b> @s.UserJoined.Count</div>
                </div>
            }

Answer 1

I fixed, I am stupid! I wanted a unique key on Schedule not a primary

I solved removing:

builder.Entity< Schedule >( e => e.HasKey( o => new {o.EventId, o.DateTime} ) );

and adding:

 builder.Entity< Schedule >( e => e.HasAlternateKey( o => new {o.EventId, o.DateTime} ) );