Configure One-to-Many Relationships Using Fluent API

In this blog, I will show you how to configure one-to-many relationships using Fluent API.

So, let’s configure one-to-many relationships using Customer and Order entities

Customer.cs

public class Customer
{
    public int CustomerId
    {
        get;
        set;
    }
    public string CustomerName
    {
        get;
        set;
    }
    public string CustomerEmail
    {
        get;
        set;
    }
    public int OrderId
    {
        get;
        set;
    }
    public virtual Order Order
    {
        get;
        set;
    }
    public Customer()
    {
    }
}

Order.cs

public class Order
{
    public int OrderId
    {
        get;
        set;
    }
    public DateTime Date
    {
        get;
        set;
    }
    public int price
    {
        get;
        set;
    }
    public virtual ICollection < Customer > Customer
    {
        get;
        set;
    }
    public Order()
    {
    }
}

Now, you can configure one-to-many relationships as shown below:

protected override void OnModelCreating(DbModelBuildermodelBuilder)
{
    // one-to-many
    modelBuilder.Entity < Customer > ().HasRequired < Order > (o => o.Order)
        .WithMany(c => c.Customer);
}

Now, I would like to add, suppose if customer and order entities don’t follow code first conventions for foreign key. For example, the customer class includes different foreign key (ex: ordId) for order entity. In this case you will proceed as follows:

protected override void OnModelCreating(DbModelBuildermodelBuilder)
{
    //one-to-many
    modelBuilder.Entity < Customer > ()
        .HasRequired < Order > (o => o.Order)
        .WithMany(c => c.Customer)
        .HasForeignKey(o => o.OrdId);
}

Before finishing, I want share with yo, how to make Nullable foreign key for one-to-many relationships. For doing this, you should write the following code as shown below:

protected override void OnModelCreating(DbModelBuildermodelBuilder)
{
    modelBuilder.Entity < Customer > ()
        .HasOptional < Order > (o => o.Order)
        .WithMany(c => c.Customer);
}

In the next blog, we learn how to configure many-to-many relationships using Fluent API.