如何编写一对多的类C＃

Question

Here is my problem: I need to represent a one to many relationship. One Company has many Stores. This is my code:

public class Company 
{
    public int Id;

    public string Name;

    public string Email;

    public Guid GUID;
}

public class Store 
{

    public int Id;

    public int CompanyId;

    public string Name;

    public int NoOfEmployees;

    public Guid GUID;
}

My question is: how this works without using virtual and hashsets? is this implementation ok?

Thank you.

Answer 1

You could use simply a List where you would save all the Stores that one company has.

public class Company 
{
    public int Id;

    public string Name;

    public string Email;

    public Guid GUID;
    // List of all Stores
    public List<Store> AllTheStores;

    public Company()
    {
        AllTheStores = new List<Store>();
    }
}

EDIT:

The property: public int CompanyId; makes only really sense if more than one Company can have the same Store . Otherwise you could access the stores via the Company:

Company c = new Company();

Store s = c.AllTheStores.Find(x=>x.Name == "MyStore");

// or 
List<Store> largeStores = c.AllTheStores.Where(x=>x.NoOfEmployees > 200).ToList();

Answer 2

As you are saying

One Company has many Stores.

In this statement your answer is.

use Company class as follow, instead of putting companyID in Store class

public class Company 
{
    public int Id;
    public string Name;
    public string Email;
    public Guid GUID;

    // put a List of all Stores
    public List<Store> Stores;
}

Answer 3

So to answer the question how this works.

Consider you have the id of the company you want to get all the stores for, you can simply do:

using (var dbcontext = new DbContext())
{
    var stores = await dbcontext.Stores.Where(x => x.CompanyId == companyId).ToListAsync();
}

You do not need navigation properties. I never have them, they have only ever caused me issues, I'm not saying they will cause you issues. They're just a convenience thing (from what it seems) which in my opinion obscures the underlying SQL representation and the queries EF could be running. Now, there are going to be few queries which you actually care about EF generating, when you get to them, you may find that navigation properties are hindering you.

If you want to save records, again, just assign each Store a real Company.Id and you will fulfill the foreign key obligations.

One change you could make (if this applies to your case) is that you can remove int Id and use the CompanyId as the primary and foreign key

public class Store 
{

    // public int Id; just remove this

    public int CompanyId; // make this a foreign key using fluent or attributes.

    public string Name;

    public int NoOfEmployees;

    public Guid GUID;
}

This makes sure you retain the 1 to Many relationship, if those many should only exist for one company . If not then don't worry about the above.

Answer 4

You should use the company class object itself instead of just having CompanyId in the Store class.

public class Company 
{
    public int Id;

    public string Name;

    public string Email;

    public Guid GUID;

    public List<Store> Stores;
}

public class Store 
{

    public int Id;

    public Company Company; // Can get CompanyId using StoreObj.Company.Id

    public string Name;

    public int NoOfEmployees;

    public Guid GUID;
}