EntityFramework Code First FluentAPI TPC

Question

Here there are my domain entities:

public class Province
{
    private ICollection<City> _cities;

    public virtual ICollection<City> Cities
    {
        get { return _cities ?? (_cities = new HashSet<City>()); }
        set { _cities = value; }
    }

    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual double Latitude { get; set; }
    public virtual double Longitude { get; set; }
}

public class City
{
    private Province _province;

    public virtual Province Province
    {
        get { return _province ?? (_province = new Province()); }
        set { _province = value; }
    }

    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual string Latitude { get; set; }
    public virtual string Longitude { get; set; }
}

Mappings:

public class ProvinceMap : EntityTypeConfiguration<Province>
{
    public ProvinceMap()
    {
        this.ToTable("Province");

        this.HasKey(p => p.Id);

        this.Property(x => x.Id).HasColumnName("Id");
        this.Property(x => x.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
        this.Property(x => x.Name).HasMaxLength(50).IsRequired();
        this.Property(x => x.Latitude).IsRequired();
        this.Property(x => x.Longitude).IsRequired();

        //this.HasMany(x => x.Cities)
        //    .WithRequired(x => x.Province)
        //    .HasForeignKey(x => x.Id);
    }
}

public class CityMap : EntityTypeConfiguration<City>
{
    public CityMap()
    {
        this.ToTable("City");

        this.HasKey(x => x.Id);

        this.Property(x => x.Id).HasColumnName("Id");
        this.Property(x => x.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
        this.Property(x => x.Name).HasMaxLength(50).IsRequired();
        this.Property(x => x.Latitude).IsRequired();
        this.Property(x => x.Longitude).IsRequired();

        this.HasRequired(x => x.Province)
            .WithMany(x => x.Cities)
            .HasForeignKey(x => x.Id);
    }
}

Context:

public class DataContext : DbContext
{
    public DataContext(): base("DataContext")
    {
        Database.SetInitializer(new MigrateDatabaseToLatestVersion<DataContext, Configuration>("DataContext"));
    }

    public DbSet<Province> Provinces { get; set; }
    public DbSet<City> Cities { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Configurations.Add(new ProvinceMap());
        modelBuilder.Configurations.Add(new CityMap());
        //base.OnModelCreating(modelBuilder);
    }
}

When I run the 'update-database' command at the Nuget Package Console, I have an error:

Invalid multiplicity in the element Role "City_Province_Source" in connection "City_Province". Because the Dependent Role refers to the key properties, the upper bound of the multiplicity properties Dependent Role must be equal to "1".

Answer 1

Logically, you are trying to define a 1-to-many relationship. Because City cannot be in many Provinces, and one Province can have many Cities.

In this case, you don't necessarily need to specify HasRequired and WithMany in your mapping.

Remove the following code from CityMap

this.HasRequired(x => x.Province)
        .WithMany(x => x.Cities)
        .HasForeignKey(x => x.Id);

Having ICollection<City> in Province table, and a property type of Province in City table is enough to establish the relationship.

The output will be like this.