Identifying the foreign key in the Entity Framework CodeFirst

Question

Identifying the foreign key in the Entity Framework CodeFirst

Navigation

#1 by (3 votes)

1

The Entity Framework identifies the foreign key through properties that have Id as part of the name or by Data Annotation [Key]. My question is, how does it identify the foreign keys and does the relationship between another table?

public class Predio {
    public int Id { get; set; }
    public string Nome { get; set; }
    public Endereco Endereco { get; set; }
}

public class Construtora {
    public Construtora()
    {
        this.Predios = new List<Predio>();
    }
    public int Id { get; set; }
    public string Nome { get; set; }
    public string RegistroCivil { get; set; }
    public List<Predio> Predios { get; set; }
}

[ComplexType()]
public class Endereco {
    public string Logradouro { get; set; }
    public string Numero { get; set; }
    public string Bairro { get; set; }
    public string Cidade { get; set; }
    public string CEP { get; set; }
}

public class Contexto : DbContext
{
    public DbSet<Predio> Predios { get; set; }
    public DbSet<Construtora> Construtoras { get; set; }
}

entity-framework

asked by anonymous 14.08.2015 / 02:33

1 answer

Required input attribute does not work after using jquery Save output after applying a replace

score 3 · Accepted Answer

Objectively speaking, through a class named ForeignKeyPropertyDiscoveryConvention . The operation is explained here .

In roughly the way that the Entity Framework performs foreign key discovery is as follows (consider that several of these steps use # ):

It is checked in the Model if there are compatible navigation properties. For example:

public virtual EntidadeEstrangeira EntidadeEstrangeira { get; set; }

If yes, it is checked in the Model if there is any candidate property being the information component of that foreign key. For example:

public int EntidadeEstrangeiraId { get; set; }

2.1. This field may not be localized. If it is not, the Entity Framework tries to look for some property that is marked with the ForeignKeyAttribute ". This Attribute can decorate both a navigation property and a data property. For example:

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

or:

[ForeignKey("EntidadeEstrangeiraId")]
public virtual EntidadeEstrageira UmNomeQualquerDePropriedadeDeNavegacao { get; set; }

Furthermore, it is checked if there is any Fluent API annotation in context. There you can also configure foreign keys.

I will not go into details of the operation because it is a lot, but in general, that's it.

Your Case

I will analyze the entities one by one.

public class Predio {
    public int Id { get; set; }
    public string Nome { get; set; }
    public Endereco Endereco { get; set; }
}

This is a classic case that falls into the first step. Normally the default is virtual for navigation properties ( I explained this here ).

As you did not define the foreign key, if the object was not a complex type , the Entity Framework would set a foreign key for you in the table corresponding to the Model Predio . If I'm not mistaken, I'd be Endereco_Id .

However, you set Endereco to a complex object. Since the ratio is 1 to 1, in the background it's as if you were defining an extension of Predio . Notice how the schema was when generating Migration :

    CreateTable(
            "dbo.Predios",
            c => new
                {
                    Id = c.Int(nullable: false, identity: true),
                    Nome = c.String(),
                    Endereco_Logradouro = c.String(),
                    Endereco_Numero = c.String(),
                    Endereco_Bairro = c.String(),
                    Endereco_Cidade = c.String(),
                    Endereco_CEP = c.String(),
                    Construtora_Id = c.Int(),
                })
            .PrimaryKey(t => t.Id)
            .ForeignKey("dbo.Construtoras", t => t.Construtora_Id)
            .Index(t => t.Construtora_Id);

Also note that you did not set a property for Construtora_Id , but reading Model Construtora , which has a ratio of 1 to N with Predio , Entity Framework has completed you would need a foreign key there, and set it to Construtora_Id (rules 1 and 2, above).

Finally, this constructor has no use:

public Construtora()
{
    this.Predios = new List<Predio>();
}

Predios is set on the Construtora data load automatically. You do not need to initialize it.