Entity Framework one to many relation code first

Question

I am having my first steps in EF 4.1. Because I was using NHibenate, the code first approach seems to me as the best one. I have problem with good mapping of one-to-many (or many-to-one) realtionship. Let's say I have 2 entities:

class ClientModel
{
    int ClientID;
    string Name;
    virtual IList<OrderModel> Orders;
}

class OrderModel
{
    int OrderID;
    string Details;
    virtual ClienModel Client;
}

When I leave it like that, there is an error while generating database - keys in tables are missing. I figured out I can fix it by changing names of the keys to ID (but it's not OK with my naming convention) or by adding [Key] annotation. Even if I add this annotation, still the names of tables are wrong - just like classes names but with 's'. So I tried to use fluent API - I made mappings. But if I set mappings just like here:

class ClientMapping
{
    ClientMapping()
    {
        this.HasKey(e => e.ClientID).Property(e => e.ID).HasColumnName("ClientID");
        this.Property(e => e.Name).HasColumnName("Name");
        this.HasMany(e => e.Orders).WithOptional().Map(p => p.MapKey("OrderID")).WillCascadeOnDelete();
        this.ToTable("Clients");
    }
}

class OrderMapping
{
    OrderMapping()
    {
        this.HasKey(e => e.OrderID).Property(e => e.OrderID).HasColumnName("OrderID");
        this.Property(e => e.Details).HasColumnName("Details");
        this.HasRequired(e => e.Client).WithMany().Map(p=>p.MapKey("Client")).WillCascadeOnDelete(false);
        this.ToTable("Orders");
    }
}

the relation betweene tables in database is doubled. What is the proper way to do one-to-many relationship using code-first approach? Am I thinking in a good direction or is it a wrong approach?

EDIT

OK, I have done it in the way @Eranga showed, but there is still a problem. When I'm getting Client from database, its Orders property is null (but in database it has some Orders with Order.ClientID == Client.ClientID).

Solution

You need to map both properties participating in the relationship. You need to add ClientID column to Orders table.

class ClientMapping
{
    ClientMapping()
    {
        this.HasKey(e => e.ClientID).Property(e => e.ID).HasColumnName("ClientID");
        this.Property(e => e.Name).HasColumnName("Name");

        this.HasMany(e => e.Orders).WithRequired(o => o.Client)
           .Map(p => p.MapKey("ClientID")).WillCascadeOnDelete();

        this.ToTable("Clients");
    }
}

class OrderMapping
{
    OrderMapping()
    {
        this.HasKey(e => e.OrderID).Property(e => e.OrderID).HasColumnName("OrderID");
        this.Property(e => e.Details).HasColumnName("Details");
        this.ToTable("Orders");
    }
}

Configuring the relationship from one entity is sufficient.

Comments

[Eranga]

I tested the configuration given in my answer and it works fine. Make sure Orders is a property not a field.

[Jo Smo]

Try virtual List<OrderModel> Orders; instead of virtual IList<OrderModel> Orders;

[rideronthestorm]

"You need to map both properties participating in the relationship. You need to add ClientID column to Orders table." What do you exactly mean by that?

[Eranga]

@rideronthestorm Orders property in ClientModel and Client property in OrderModel as the two participants of the relationship.

[rideronthestorm]

I still don't understand it. Wasn't I mapping both of them? Maybe you could post full code for it? And why do I need ClientID in Orders (OrderModel?)?

[Eranga]

@rideronthestorm I posted the full code for mapping. The way you mapped will be interpreted by EF as two different relationships. Since an Order requires a Client you need to added the foreign key column ClientID to Order table

[rideronthestorm]

Isn't ClienModel Client; enough as a foreign key?

[rideronthestorm]

Amd ypu are saying that I should put int ClientID instead of ClientModel Client? Why there is no Client or ClientID mapping?

[rideronthestorm]

And the other question is what is the difference if I set hasMany in client or withMany in order? These are 2 different ways to describe the same relation?

[rideronthestorm]

I did it like you said - so model has no changes, but mappnigs are like the ones you've posted. The database was generated without errors, but there is something wrong with it, because when I try to generate diagram for it in SQl Management Studio, I get the error "The table '<table_name>' no longer exists in the database" for each of my generated tables. However, they are accessible, I can see their columns, modify them, etc.

[Eranga]

@rideronthestorm You do not ned to add ClientID property to OrderModel. EF will create a column ClientID in Orders table when you map the entities as I have shown. HasMany is used when you map from the many side. WithMany is used when you map form one side of the relationship to the many side.

[rideronthestorm]

"HasMany is used when you map from the many side. WithMany is used when you map form one side of the relationship to the many side." - yes, I know that, but what is the difference in effect? In my example could I use withMany in Client instead of hasMany in order and effect (objects generated) would be the same?