EntityFramework Code First 1 to 1 data add

Question

I'm creating a database using the code-first way. I have two entities in a 1 to 1 relation, but I don't really know how to instantiate them.

Assume those are my entities:

public class Foo
{
    [Key]
    public int Id {get;set;}
    [ForeignKey("BigFoo")]
    public int BigFooId {get;set;}
    public virtual BigFoo BigFoo {get;set;}
}

public class BigFoo
{
    [Key]
    public int Id {get;set;}
    [ForeignKey("Foo")]
    public int FooId{get;set;}
    public virtual Foo Foo {get;set;}
}

This is my code:

Foo foo = new Foo();
foo = db.Foo.Add(foo);

BigFoo big = new BigFoo {Foo = foo, FooId = foo.Id};
big = db.BigFoo.Add(big);

//HERE is my doubt
//I don't know if I have to add the relation also in the Foo object
//Do i need the following code?

//foo.BigFoo = big;
//foo.BigFooId = big.Id;
//db.Foo.Attach(foo);
//var entry = db.Entry(foo);
//entry.Property(x => x.BigFoo).IsModified = true;

db.SaveChanges();

The relation is already set in my BigFoo object declaration, do I need anyway to set this relation also in the Foo object or it will be automatically assigned?

Thanks all for the help.

EDIT:

I have another doubt: I have my foreign keys named relatedentityIdField.

I have to istantiate also them with the

foo.BigFooId = big.Id;

Or those relations are automatically filled?

ADD EXAMPLE-EDIT

An example can be the relation Nation - President

Every Nation has only one president, and every president is only the president of a Nation.

How can I set this relation using Code-First?

Answer 1

With current model what you really have is two one to many unidirectional relationships. To create a one to one relationship using Code First you must define the PK of the dependent entity as FK of the relationship too (check this link for a detailed explanation).

public class Foo
{
  public int Id{get;set;}

  public virtual Boo Boo {get;set;}
}

public class Boo
{
  [Key, ForeignKey("Foo")]
  public int FooId{get;set;}

  public virtual Foo Foo {get;set;}
}

With this model, you could add data as follows:

1. If you want to create a new Foo and Boo and you want to relate them, you can do the following:

    var boo=new Boo(); var foo=new Foo{Boo=boo }; context.Foos.Add(foo); context.SaveChanges(); 

You should see Foo navigation property in your Boo entity is also filled.

2. If Foo already exist and you want to create a new Boo related with that foo:

   You can set the Boo navigation property in your foo entity:

    var foo= context.Find(yourId); foo.Boo=new Boo(); context.SaveChanges(); 

   Or you can just set the PK/FK property of your new Boo entity:

     var fooId=1;// You already have the Foo id var boo = new Boo() { FooId = fooId}; context.Boos.Add(boo); context.SaveChanges(); 

Whit your model, as I said before, you have two different relationships, so your navigation properties aren't really related. If you want to prove that, add two collections to your entities:

public class Foo
{
    [Key]
    public int Id {get;set;}
    [ForeignKey("BigFoo")]
    public int? BigFooId {get;set;}
    public virtual BigFoo BigFoo {get;set;}
    public virtual ICollection<BigFoo> BigFoo{get;set;}// Add this property
}

public class BigFoo
{
    [Key]
    public int Id {get;set;}
    [ForeignKey("Foo")]
    public int? FooId { get; set; }
    public virtual Foo Foo {get;set;}
    public virtual ICollection<Foo> Foos{get;set;}// Add this property
}

And later try this:

using (var context=new MyContext())
{
    var foo = new Foo();
    context.Foos.Add(foo);
    context.SaveChanges();

    var boo = new BigFoo() { FooId = foo.Id};

    context.Boos.Add(boo);
    context.SaveChanges();
 }

After the last SaveChanges you will Foo nav. property in boo instance and BigFoos nav property in foo instance are properly filled.

Notes: I changed your navigation properties to virtual to meet one of the requirements of Lazy Loading , and I also changed your FK properties as nullables to avoid cycles of cascading delete. Code First did not setup a cascade delete for the optional relationships.