ASP.NET 核心将带有链接数据的实体传递给查看和返回

Question

I'm passing an object with a N:M relationship to a view:

public class Project
{
    [Key]
    public int ProjectId { get; set; }
    ...    
    public virtual ICollection<CrewMember> CrewMembers { get; set; }
}

In the controller, I eager load the collection and pass the object to the view:

public IActionResult Modify(int? id)
{
    var obj = _db.Projects.Where(i => i.ProjectId == id).Include(c => c.CrewMembers).First();
    return View(obj);
}

The view looks like this:

<div class="col-md-7">
    <form method="post" enctype="multipart/form-data">
        <input asp-for="ProjectId" hidden />
        <input asp-for="CrewMembers" hidden />
        ...
        <button type="submit">Update</button>
    </form>
</div>

The data seems to "arrive" on the view just fine (if I look at the Model object, it contains the CrewMembers collection), however when I submit the form, the "Projects" collection returns empty:

//POST
[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult Modify(Project obj)
{
    //obj.CrewMembers IS NOW EMPTY(!)

    _db.Projects.Update(obj);
    _db.SaveChanges();

    return RedirectToAction("Index");
}

So how can I preserve the Collection when passing it to/from the view? It seems the <input asp-for="CrewMembers" hidden /> trick doesn't work...

Answer 1

Try:

[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult Modify([Bind("ProjectId,CrewMembers")]Project obj)
{
    //obj.CrewMembers IS NOW EMPTY(!)

    _db.Projects.Update(obj);
    _db.SaveChanges();

    return RedirectToAction("Index");
}

And in the view, use one input for each element of the list.

@for(int i=0;i<Model.CrewMembers.Count();i++)
{
<input type="hidden" asp-for="CrewMembers[i].xxxx"/>
<input type="hidden" asp-for="CrewMembers[i].xxxx"/>
<input type="hidden" asp-for="CrewMembers[i].xxxx"/>
...
}