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.