MVC 5中的模型绑定问题

Question

I'm having some issues when performing create operations with code-first.

I have these classes.

[Table("Localidades")]
public class Localidad
{
    public Localidad() { 
    }

    public int LocalidadId { get; set; }

    [Required]
    [StringLength(150)]
    [Display(Name = "Nombre")]
    public string nombre { get; set; }

    public Provincia ProvinciaId { set; get; }
}

[Table("Provincias")]
public class Provincia
{
    public Provincia() { 
    }

    public int ProvinciaId { set; get; }

    [StringLength(150)]
    [Display(Name = "Nombre")]
    public string nombre { set; get; }
}

[Table("Domicilios")]
public class Domicilio
{
    public Domicilio() { 
    }

    public int DomicilioId { get; set; }

    [StringLength(150)]
    [Display(Name = "Calle")]
    public string calle { get; set; }

    [Display(Name = "Número")]
    public int numero { get; set; }

    [Display(Name = "Piso")]
    public int piso { get; set; }

    [Display(Name = "Departamento")]
    public char dpto { get; set; }

    [Display(Name = "Código Postal")]
    public int codigoPostal { get; set; }

    [Display(Name = "Localidad")]
    public Localidad LocalidadId { get; set; }
}

and

[Table("Personas")]
public  abstract class Persona
{
    public Persona() { 
    }

    [Key]
    public int ID { set; get; }

    public Domicilio DomicilioId { set; get; }

    [Required]
    [StringLength(150)]
    public string nombre { set; get; }

    [Required]
    [StringLength(40)]
    public string nroDocumento {get;set;}

    [Required]
    [StringLength(150)]
    public string apellido  {get;set;}

    public DateTime? fechaNacimiento {get;set;}

    public long telefonoFijo {get;set;}

    public long telefonoMovil {get;set;}

    [EmailAddress]
    public string email {get;set;}

    [Display(Name = "Sexo")]
    public char sexo {get;set;}

    [DataType(DataType.Date)]
    public DateTime? fechaAlta {get;set;}

    [DataType(DataType.Date)]
    public DateTime? fechaBaja { get;set;}
}

Localidad has a FK to Provincia, Domicilio has a FK to Localdiad and Persona has a FK to Localidades. So far so good the database schema is correct.

When I try to create a new person my code is the following: (I got the id from a ddl that is working)

var localidad = db.Localidades.Find(model.LocalidadId);
var domicilio = new Domicilio { calle = "estrada", dpto = 'a', LocalidadId = localidad };
var user = new ApplicationUser { UserName = model.nroDocumento.ToString(), Email = model.Email };
var paciente = new Paciente
{
    nombre = model.Nombre,
    apellido = model.Apellido,
    fechaAlta = DateTime.Now,
    nroDocumento = model.nroDocumento,
    DomicilioId = domicilio
};

With the id I got from the model (it is the correct id of the chosen Localidad), I retrieve the Localidad from the database and assign it to domicilio model.

The thing is that instead of linking the model to the appropriate Localidad in the database (using the FK) it creates a new register in the data base.

I know this is some misconception of the way code-first works so if anyone could point me in the right direction I'll be so grateful.

Answer 1

Ok so first of all in Entity Framework, you will use navigation properties rather than foreign keys. For performance and efficiency purposes, every single navigation property should lazyload since you don't want the EF to load every single navigation properties until you actually need them. You can achieve that by adding the keyword "virtual". In your Localidad:

public virtual Provincia Provincia { set; get; }

It is preferable to use the object name since this property is actually pointing at an instance of a Provincia object rather than being an ID.

In a one to many relationship like I am assuming the Provincia - localida relationship to be,you also need to include a collection in the one end.

In your Provincia model:

public Provincia()
{
     this.Localidads = new HashSet<Localidad>();
}
public virtual ICollection<Localidad> Localidads { get; set; }

Here we're also adding a constructor to initialize the Localidads collection

Now that we have set up a proper one-to-many relationship, update your database with a migration.

As for the way to add an object(Localidad) for exemple, you were about right on that part: create an object(Localidad) variable, fill it's scalar properties(non navigation).

To add a navigation property, you can either find it in your context or search it using the where method:

Localidad.Provincia = db.Find(yourprovinciaID);

That's assuming you have the ID in hand. If you don't you can search it using any scalar property:

Localidad.Provincia = db.Provincias.Where(x=> x.attribute == attributevalue ).FirstOrDefault<Provincia>();

Once our object instance (Localidad in this exemple) has it's values filled, we can now add it to the context and save it to the database.

context.Localidads.Add(Localidad);
context.SaveChanges();

The localidad will automatically be added to the collection in the corresponding provincia and Entity Framework will take care of foreign key matters for you.

What I just explained is basically how to make one to many relationships work. If you want to use many-to-many or one-to-one relationships, I'd recommand looking up the Fluent API doc: msdn.microsoft.com/en-US/data/jj591620 .

I am sorry if that is not clear to you and am willing to answer your questions.