如何使用清单 <model> 通过引用而不是通过价值？

Question

OK. I have State which has List. I want to have multiple instances of State that use the same list of Series.

public class State
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Series> Serieses { get; set; }
}

public class Series
{
    public int Id { get; set; }
    public string Name { get; set; }
}

After Creating a State by typing in the Name of the State and selecting 1 or more Series from a ListBox:

public ActionResult Create(State state, FormCollection form)
    {

      // method to get selected Series from db

      foreach (var sItem in seriesModel//List of Possible Series)
      {
          foreach (var item in Selections//User selected Series)
          {

             if (sItem.Name == item.Name)
             {
                newSeries.Add(sItem);
             }
          }
      }

      state.Serieses = newSeries;
      _db.Entry(state).State = EntityState.Modified;
      _db.SaveChanges();

The problem is after I create one instance of State with List. If I create a second instance and use the same Series in its list, the first will lose that Series in its list. So obviously Series is being passed by value and not reference. I'm new to C#, but back in C++ we would use pointers. That way if I change the original values of Series it will show up on each State list that points to it. I've also noticed in the Table Data in the Database, it has added a Foreign Key State_Id to every Series. Here's the Table Definition it created when I used Code First method.

CREATE TABLE [dbo].[Series] (
[Id]       INT            IDENTITY (1, 1) NOT NULL,
[Name]     NVARCHAR (MAX) NULL,
[State_Id] INT            NULL,
CONSTRAINT [PK_dbo.Series] PRIMARY KEY CLUSTERED ([Id] ASC),
CONSTRAINT [FK_dbo.Series_dbo.States_State_Id] FOREIGN KEY ([State_Id]) REFERENCES [dbo].[States] ([Id])

Answer 1

As quoted here , "The ref keyword causes an argument to be passed by reference, not by value."

An ugly way to use this would be something like the following, since you can't change the declaration of value :

public MyClass {
    private string myString;

    public void SetMyString(ref string str) {
        myString = str
    }
}

I don't really suggest this though.

Answer 2

使其静态如何？

public static ICollection<Series> Serieses { get; set; }

Answer 3

If you're not looking to alter the list differently for each instance, use a static list. You can just access it like this.

State.Serieses

Answer 4

Use the AddRange() method

//replace 'state.Serieses = newSeries;' with
state.Serieses.AddRange(newSeries);

Make sure in the constructor for state than you initialize Serieses with a new empty series.

BTW Serieses is not word. The plural of Series is Series .

Update

I don't know why you need interfaces for the collections and cannot just use List<Series> . That part has not been explained. Also why virtual ?

Here is skeleton code on how to keep the same collection and use AddRange()

// StackOverflow 16764155
public class Series
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class State
{
    public State()
    {
        Serieses = new List<Series>();
    }
    public int Id { get; set; }
    public string Name { get; set; }
    public List<Series> Serieses { get; set; }
}

public class DbForm
{
    public IEnumerable<Series> Selection { get; }
}

public class DbLogic
{

    public void Create(State state, IEnumerable<Series> selection)
    {
        state.Serieses.AddRange(selection);

        // do db stuff
        // _db.Entry(state).State = EntityState.Modified;
        // _db.SaveChanges();
    }
}


class Program
{
    static void Main(string[] args)
    {
        var form = new DbForm();
        var state = new State();
        var db = new DbLogic();
        // stuff here
        var sel = form.Selection;
        db.Create(state, sel);
    }
}

Answer 5

Using Entity Framework with Code First you will have to add a collection of States to your series as well in order to generate a many-to-many relationship table.

public class Series
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<State> States { get; set; } 
}

You will have to run a code first data migration as well using the package manager console.

Add-Migration <YourMigrationNameHere>

Resulting in the following DB structure after you run your app next: