I have been attempting to use EF Code First to create and manage my Database for a project I am working on. I have, however, encountered a slight issue.
public class Planet
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ID { get; set; }
[Required]
public string Planet_Name { get; set; }
[Required]
public int Planet_X { get; set; }
[Required]
public int Planet_Y { get; set; }
[Required]
public string Planet_Desc { get; set; }
public virtual ICollection<Mineral> Minerals { get; set;}
}
public partial class Mineral
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ID { get; set; }
[Required]
public string Name { get; set; }
[Required]
public string Symbol { get; set; }
[Required]
public string Mineral_Desc { get; set; }
[Required]
public int rate { get; set; }
[Required]
public decimal ratio { get; set; }
}
When using the above, The Mineral table acquires a Planet_Id Column Set as a ForeignKey. This, of course, has the side-effect of causing an error to be thrown when 2 planet have the same mineral. What I need is to allow multiple planets to share a Mineral. While the Planet needs to know what Minerals it has, the Mineral has no reason to know what Planets it is on.
My question therefore is, how do I go about doing that? (Note: I have attempted to add a public virtual Planet to the Mineral class, it changes nothing.)
you need to add a ICollection<Planet> Planets
in your Mineral
class :
public class Mineral
{
public Mineral()
{
Planets = new HashSet<Planet>();
}
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ID { get; set; }
[Required]
public string Name { get; set; }
[Required]
public string Symbol { get; set; }
[Required]
public string Mineral_Desc { get; set; }
[Required]
public int rate { get; set; }
[Required]
public decimal ratio { get; set; }
public virtual ICollection<Planet> Planets { get; set; }
}
Also in your Planet
class, you should add a default constructor :
public class Planet
{
public Planet()
{
Minerals = new HashSet<Mineral>();
}
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ID { get; set; }
[Required]
public string Planet_Name { get; set; }
[Required]
public int Planet_X { get; set; }
[Required]
public int Planet_Y { get; set; }
[Required]
public string Planet_Desc { get; set; }
public virtual ICollection<Mineral> Minerals { get; set; }
}
So In your DbContext, you need to define both entity Planet
and Mineral
and create a many to many relation by overriding the OnModelCreating
function:
public class PlanetContext : DbContext
{
public DbSet<Planet> Peoples { get; set; }
public DbSet<Mineral> Minerals { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Planet>()
.HasMany(p => p.Minerals)
.WithMany(m => m.Planets)
.Map(t => t.MapLeftKey("PlanetID")
.MapRightKey("MineralID")
.ToTable("PlanetMineral"));
}
}
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