CODEWITHSUNDEEP
c#asp.netentity-frameworkef-code-firstone-to-many
Kgn-web
Kgn-web

Reputation: 7555

how to write one to many relationship in code

I am using EF CodeFirst approach for quite long. This is how I used to define one to many relationship.

//one Customer can have many products --> One to Many relationship.
public class Customer
{
    [Key]
    public int CustId { get; set; }
    public string CustName { get; set; }
    public virtual List<Product> Products { get; set; }
}

public class Product
{
    [Key]
    public int ProdId { get; set; }
    public string BuyDate { get; set; }
    [ForeignKey("Customer")]
    public int CustomerId { get; set; }
    public virtual Customer Customer { get; set; }
}

But recently while one discussion, I came to know that this is not the best approach. There is a way where I can define such relationship without overhead of public int CustomerId { get; set; } in Product Entity.

How do I do this?

Upvotes: 1

Views: 986

Answers (2)

middelpat
middelpat

Reputation: 2585

When you define the relationship as following it should be enough to create a one-to-many relationship between product and customer

public class Customer
{
    //other properties omitted
    public virtual ICollection<Product> Products { get; set; }
}

public class Product
{
    //other properties omitted
    [ForeignKey("Customer")]
    public int CustomerId { get; set; }
    public virtual Customer Customer { get; set; }
}

In EF you can then set this relationship (for a new product) in the following ways:

var customer = context.Customers.GetById(1);
var myProduct = new Product()
{
    //set all the properties
}

customer.Products.Add(myProduct);
context.SaveChanges();

When you have loaded a product with EF, you can acces the customer (and all its properties) just by navigating to it:

string name = myProduct.Customer.CustName;
int custId = myProduct.Customer.Id;

note that querying the products dbset and looking at the customerId causes the generated SQL to perform a join to the customers table which can have a negative effect on performance.

I don't find your example to be a bad solution. I think that in some cases it makes sense to include the CustomerId in your model (it is created in the database anyway by EF to create the relationship).

Upvotes: 1

Akos Nagy
Akos Nagy

Reputation: 4350

Just leave out the CustomerId property from Product, and rename the primary key in Customer to CustomerId.

Upvotes: 0

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