C#•7d ago

✅ Why for some navigation properties, we use setters while for some we initialise a list

Hello guys, consider the following two models that will be used to create a member table and lending table using EF Core. My question is, why for the navigation propery, when a collection is used like ICollection, we don't need to use set in the curly braces, while if it's a single object, like Books? Book, we use get and set. What's the difference here please. We directly assign a new list when using collection for example.

C#
namespace Week5.Models;

public class Member
{
    public int MemberId { get; set; }
    public string FirstName { get; set; } = null!;
    public string LastName { get; set; } = null!;
    
    // Navigation property - One member can have many lendings
    public ICollection<Lending> Lendings { get; } = new List<Lending>();
}

C#
namespace Week5.Models;

public class Member
{
    public int MemberId { get; set; }
    public string FirstName { get; set; } = null!;
    public string LastName { get; set; } = null!;
    
    // Navigation property - One member can have many lendings
    public ICollection<Lending> Lendings { get; } = new List<Lending>();
}

C#
namespace Week5.Models;

public class Lending
{
    public int LendingId { get; set; }
    public DateTime IssueDate { get; set; }
    public DateTime DueDate { get; set; }
    public DateTime ReturnDate { get; set; }
    
    // Foreign keys
    public int MemberId { get; set; }
    public int BookId { get; set; }
    
    // Navigation property - one lending can have one member; one lending can have one book;
    public Books? Book { get; set; }
    public Member? Member { get; set; }
    
}

C#
namespace Week5.Models;

public class Lending
{
    public int LendingId { get; set; }
    public DateTime IssueDate { get; set; }
    public DateTime DueDate { get; set; }
    public DateTime ReturnDate { get; set; }
    
    // Foreign keys
    public int MemberId { get; set; }
    public int BookId { get; set; }
    
    // Navigation property - one lending can have one member; one lending can have one book;
    public Books? Book { get; set; }
    public Member? Member { get; set; }
    
}

6 Replies

Jimmacle•7d ago

because it's not necessary to assign a new collection to modify the items inside that's not really an EF thing, it's just a "how you want to expose collections in a class" thing

FakerOP•7d ago

hmmm yeah, each time we use the same collection that we initialized when creating a lending object; we can add to the list or remove to it without needing another reference? But hmm I'm still confuse, why for books we don't do that? :c

Angius•7d ago

Because it's not a list Or any other sort of collection

FakerOP•7d ago

yep I see last question, notice the collection is not nullable, like we didn't use the ? together with the collection, is there a use-case where we would want a list to be nullable? well no I think it's counter-intuitive... we are assigning a new list, the idea is we do that so that we don't have to check for null reference; we don't want to have a NullPointerException?

Angius•7d ago

Yeah, the list is instantiated in every case, it will never be null

FakerOP•7d ago

Yep, thanks !

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✅ Why for some navigation properties, we use setters while for some we initialise a list

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