使用实体框架一对一的外键

Question

The Customer can have only one Language . I don't find the right way to create the key. When I get an object Customer the property LanguageId has a content but not the property Language . I use EF 6.1

This Language object will be use in other object.

I did this :

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
    modelBuilder.Configurations.Add(new CustomerMap());
    modelBuilder.Configurations.Add(new LanguageMap());   
}

public class Customer
{
    public int CustomerID { get; set; }
    public string Code { get; set; }

    public int LanguageId { get; set; }
    [ForeignKey("LanguageId")]
    public Language Language { get; set; }
}

public class CustomerMap : EntityTypeConfiguration<Customer>
{
    public CustomerMap()
    {
        this.HasKey(t => t.CustomerID);

        // Properties
        this.Property(t => t.CustomerID).IsRequired();
        this.Property(t => t.Code).IsRequired();

        // Table & Column Mappings
        this.ToTable("Customer");
        this.Property(t => t.CustomerID).HasColumnName("CustomerID");
        this.Property(t => t.Code).HasColumnName("Code");
    }
}

public class Language
{
    public int LanguageID { get; set; }
    public string Code { get; set; }
}

public class LanguageMap : EntityTypeConfiguration<Language>
{
    public LanguageMap()
    {
        this.HasKey(t => t.LanguageID);
        this.Property(t => t.Code).IsRequired();
    }
}

Update (Language will be used in other object)

Answer 1

You can achieve one to one with two options, but first you have to remove the foreign key value in the principal. Principal means that the record must exist first, that's why this entity doesn't need to have foreign key value, just foreign key reference.

Remove this code.

 public int LanguageId { get; set; } [ForeignKey("LanguageId")] 

First . After removing above code add this configuration.

 modelBuilder.Entity<Customer>() .HasRequired(a => a.Language) .WithRequiredPrincipal(); 

Second , also add the foreign key reference on dependent ( Language ).

 public Customer Customer { get; set; } 

Then mention the principal reference in WithRequiredPrincipal .

 modelBuilder.Entity<Customer>() .HasRequired(a => a.Language) .WithRequiredPrincipal(x => x.Customer); 

update

To load language you can do it with lazy loading by adding virtual keyword (the context configuration must also enable lazy loading and proxy).

 public virtual Language Language { get; set; } 

Or do with eager loading.

 var customerID = 5; var customer = db.Set<Customer>().Include(c => c.Language) .FirstOrDefault(c => c.CustomerID == customerID);