如何播种外键一对多列表关系？

Question

I have class/table:

public class Song
{
    [Key]
    public Guid Id { get; set; }
    [Required]
    public string Name { get; set; }
    [ForeignKey("FK_SongTags")]
    public List<Tag> Tags { get; set; }
}

Where class/table Tag is:

[Table("Tags")]
public class Tag
{
    [Key]
    public string Name { get; set; }
}

In my Context I call this seed:

modelBuilder.Entity<Song>().HasData(new List<Song>
{
    new Song { Id = Guid.NewGuid(), Name = "Some random song", Tags = new List<Tag> { "pop", "rock" } }
});

When I do do.net ef database update , I get:

The seed entity for entity type 'Song' cannot be added because it has the navigation 'Tags' set. To seed relationships, add the entity seed to 'Tag' and specify the foreign key values {'FK_SongTags'}. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the involved property values.

How do I solve this error?

Answer 1

You need many-to-many relations since one song can have several tags, and each tag can be used for another songs too. Try this:

public class Song
{
    [Key]
    public Guid Id { get; set; }
    [Required]
    public string Name { get; set; }
  
    public virtual List<Tag> Tags { get; set; }
}


[Table("Tags")]
public class Tag
{
    [Key]
    public string Name { get; set; }
    public virtual List<Song> Songs{ get; set; }
}

you will have to make an initial migration to db after making changes.

but if you still think that you need one to many try this

[Table("Tags")]
public class Tag
{
    [Key]
    public string Name { get; set; }

    public Guid SongId {get; set;}
     public virtual Song Song {get; set;}

}