不包含“添加”的定义

Question

I'm trying to make the same thing like in this thread, but I'm getting error:

'System.Collections.Generic.IEnumerable' does not contain a definition for 'Add' and no extension method 'Add' accepting a first argument of type 'System.Collections.Generic.IEnumerable' could be found (are you missing a using directive or an assembly reference?)

Here is my code:

[HttpPost]
public ActionResult Create(ANIME anime)
{
    var db = new MainDatabaseEntities();
    var newanime = new ANIME
    {
        ID_AN = anime.ID_AN,
        TITLE_OR = anime.TITLE_OR,
        TITLE_EN = anime.TITLE_EN,
        GENRES = new List<GENRES>()
    };

    foreach (var selectedAnime in anime.GENRES.Where(c => c.isSelected))
    {
        var genre = new GENRES { ID_GE = selectedAnime.ID_GE };
        db.GENRES.Attach(genre);
        newanime.GENRES.Add(genre); <--- this is the error line
    }

    db.ANIME.Add(newanime);
    db.SaveChanges();
    return RedirectToAction("Index");
}

ANIME:

public partial class ANIME
{
    public int ID_AN { get; set; }
    public string TITLE_OR { get; set; }
    public string TITLE_EN { get; set; }

    public virtual IEnumerable<GENRES> GENRES { get; set; }
}

GENRES:

public partial class GENRES
{
    public int ID_GE { get; set; }
    public string GENRE { get; set; }
    public bool isSelected { get; set; }
    public virtual ICollection<ANIME> ANIME { get; set; }
}

The error is in the line newanime.GENRES.Add(genre) in HttpPost . I added using System.Linq to all models and controllers but it doesn't help. Any ideas how to resolve this?

EDIT:

After repairing this a new error arrived. I think it's not related to above one but I don't want to spam unnecessary threads.

Error message:

The entity or complex type 'MainDatabaseModel.GENRES' cannot be constructed in a LINQ to Entities query.

Related code:

public ActionResult Create()
{
    var db = new MainDatabaseEntities();
    var viewModel = new ANIME
    {
        GENRES = db.GENRES.Select(c => new GENRES
        {
            ID_GE = c.ID_GE,
            GENRE = c.GENRE,
            isSelected = false
        }).ToList()
    };
    return View(viewModel);       
}

Answer 1

You have a IEnumerable property that you're initialising with a List. The List class implements the IEnumerable interface.

When you are invoking something like this:

IEnumerable myList = new List<MyType>();

you're saying that you want for your object the features of the IEnumerable interface that are also inherited in the List class. In this case, the method Add isn't part of the IEnumerable interface, because it's a method of the List class only, and you have that exception.

You have then to change the type of your property, from IEnumerable<YourType> to IList<YourType> (more info about IList here ). In this way, the exception about Add method won't be thrown.

Answer 2

Try this:

public partial class ANIME
{

    public int ID_AN { get; set; }
    public string TITLE_OR { get; set; }
    public string TITLE_EN { get; set; }

    public virtual ICollection<GENRES> GENRES { get; set; } // Use ICollection here
}

Answer 3

The answer for your second question is that you cannot (and should not be able to) project onto a mapped entity. You can, however, project onto an annonymous type or on data transfer object.

See this thread: The entity cannot be constructed in a LINQ to Entities query

Also, please do not extend your initial question with a totally new, unrealted one in the future. It makes it hard to follow...

Answer 4

IEnumerable<> is just a sequence of items. You can't add items to it and you can't remove items from it. You can query it.

If you need to add items, you will need a collection implementing at least the ICollection<> interface or IList<> interface.

Good news is that you can use IEnumerable<> there like as follows

var list = new List<GENRES>();
var newanime = new ANIME
{
    ID_AN = anime.ID_AN,
    TITLE_OR = anime.TITLE_OR,
    TITLE_EN = anime.TITLE_EN,
    GENRES = list
};

list.Add(genre);

But this has limited possibilities. You won't be able to add new items once you leave the scope and loose a reference to the local list variable.