Entity Framework - 3 tables have relationships with each other - entity-framework

Question

I have 3 tables as follows:
ApplicationUser:
public class ApplicationUser : IdentityUser
{
..some basic properties..
// navigation properties
public virtual ICollection<Post> Posts { get; set; }
public virtual ICollection<Album> Albums { get; set; }
}
Post:
public class Post
{
public long Id { get; set; }
public string Content { get; set; }
public int? AlbumId { get; set; }
public string UserId { get; set; }
public virtual ApplicationUser User { get; set; }
public virtual Album Album { get; set; }
}
Album:
public class Album
{
public int Id { get; set; }
public string Name { get; set; }
public string UserId { get; set; }
public virtual ApplicationUser User { get; set; }
public virtual ICollection<Post> Posts { get; set; }
}
and finally ApplicationDbContext:
modelBuilder.Entity<ApplicationUser>()
.HasMany(a=>a.Posts)
.WithRequired(a=>a.User)
.HasForeignKey(a=>a.UserId)
.WillCascadeOnDelete(false);
modelBuilder.Entity<Post>()
.HasKey(p => p.Id);
modelBuilder.Entity<Album>()
.HasKey(a => a.Id);
modelBuilder.Entity<ApplicationUser>()
.HasMany(u=>u.Albums)
.WithOptional()
.HasForeignKey(a=>a.UserId)
.WillCascadeOnDelete();
modelBuilder.Entity<Album>()
.HasMany(a=>a.Posts)
.WithRequired()
.HasForeignKey(p=>p.AlbumId)
.WillCascadeOnDelete();
When I run the migration and update database, I get an error:
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint
"FK_dbo.Posts_dbo.Albums_AlbumId". The conflict occurred in database
"aspnet-Link-20161012104217", table "dbo.Albums", column 'Id'.
Could anyone tell my why they conflict? It seems pretty legit to me.

Answer 1

In your code you set AlbumId as nullable but in configuration defined WithRequeired():
public class Post
{
public long Id { get; set; }
public string Content { get; set; }
public int? AlbumId { get; set; } //<-- this one
public string UserId { get; set; }
public virtual ApplicationUser User { get; set; }
public virtual Album Album { get; set; }
}
modelBuilder.Entity<Album>()
.HasMany(a=>a.Posts)
.WithRequired() //<-- this one
.HasForeignKey(p=>p.AlbumId)
.WillCascadeOnDelete();
If AlbumId is nullable you should change the configuration:
//Ef by default conventions set the AlbumId as foreign key
modelBuilder.Entity<Album>()
.HasMany(a=>a.Posts)
.WithOptional(a=>a.Album);
and if AlbumId isn't nullable change the property:
public class Post
{
public long Id { get; set; }
public string Content { get; set; }
public int AlbumId { get; set; }
public string UserId { get; set; }
public virtual ApplicationUser User { get; set; }
public virtual Album Album { get; set; }
}
and use following configuration:
//Ef by default conventions set the AlbumId as foreign key
modelBuilder.Entity<Album>()
.HasMany(a=>a.Posts)
.WithRequired(a=>a.Album)
.WillCascadeOnDelete();