Configure Relationship in Entity Framework using Fluent API

One-to-zero or one relationship using Fluent API

Let’s configure one-to-zero or one relationship using Customer and Customer Address entities.

Customer.cs

public class Customer
{
    publicintCustomerId
    {
        get;
        set;
    }
    public string CustomerName
    {
        get;
        set;
    }
    public string CustomerEmail
    {
        get;
        set;
    }
    public CustomerAddressCustomerAddr
    {
        get;
        set;
    }
    publicCustomer()
    {
    }
}

CustomerAddress.cs

public class CustomerAddress
{
    public int CustomerAddressId
    {
        get;
        set;
    }
    public string Address
    {
        get;
        set;
    }
    public string City
    {
        get;
        set;
    }
    public CustomerCustomer
    {
        get;
        set;
    }
    public CustomerAddress()
    {
    }
}

Now, we can pass to configure one to one or zero relationship using code as shown below:

protected override void OnModelCreating(DbModelBuildermodelBuilder)
{
    // Now, I will configure Customer &CustomerAddress entities
    modelBuilder.Entity < Customer > ()
        .HasOptional(c => c.CustomerAddr)
        .WithRequired(Ad => Ad.Customer);
}

• HasOptional (c=>c.CustomerAddr) indicates that Address is optional for customer entity.
  
• WithRequired (Ad=>Ad.Customer) indicates that Customer property is required for Customer Address entity then you can understand that you cannot save Customer Address without Customer.

Note

One-to-one is not possible in MS SQL Server. EF creates one-to-zero or one relationship on entities not in database.



At this level, I would like to share with you the following question:

If CustomerAddressId does not follow primary key convention (className<Id>), how can we do to handle this problem?

Now, let’s consider the following Customer & CustomerAddress entities.

public class Customer
{
    public int CustomerID
    {
        get;
        set;
    }
    public string CustomerName
    {
        get;
        set;
    }
    public string CustomerEmail
    {
        get;
        set;
    }
    public CustomerAddressCustomerAddr
    {
        get;
        set;
    }
    public Customer()
    {
    }
}
public class CustomerAddress
{
    public int Id
    {
        get;
        set;
    }
    public string Address
    {
        get;
        set;
    }
    public string City
    {
        get;
        set;
    }
    public CustomerCustomer
    {
        get;
        set;
    }
    public CustomerAddress()
    {
    }
}

So, to overcome this problem, we need to add line which specifies Id property is considered as primary key.

protected override void OnModelCreating(DbModelBuildermodelBuilder)
{
    //Configure Id as primary key for customerAddress entity
    modelBuilder.Entity < CustomerAddress > ().HasKey(CA => CA.Id);
    modelBuilder.Entity < Customer > ()
        .HasOptional(c => c.CustomerAddr)
        .WithRequired(Ad => Ad.Customer);
}