code首先，与工作的关系，播种 [英] Code first, working with relationships, seeding

问题描述

我想简单地创建一个已经存在两个实体之间的关系。

I would like to simply create a relationship between two entities that already exists..

在我的情况我有可能有多个流派（也就是一堆的实体）的专辑实体

In my case I have an Album entity which might have multiple Genres(which also is a bunch of entities)

我的相册样板看起来是这样的：

My Album model looks like this:

public class AlbumModel : IModel
{
    public List<GenreModel> Genres { get; set; }
    public ArtistModel Artist { get; set; }
    public Guid Id { get; set; }
    public string Title { get; set; }
    public float Price { get; set; }
    public string ArtUrl { get; set; }
}

然后我想一个相册样板对象和一堆GenreModel对象之间建立的关系船/实体。

I then want to create a relation ship between a Album model-object and a bunch of GenreModel-objects/entities..

在正常的实体框架我只是分配一个新的EntityKey ..但是我不太清楚如何先做到这一点使用code ..
我还注意到，有些人有一个名为xxxxId一个额外的属性，他们希望创造之间的参考实体..然后简单地分配一个值到一些如何神奇地创造..实体之间的参考xxxxId财产，我想这对于一对一或一对多的关系正常工作..但我想，对于很多不工作的许多relationship..or？

In the "normal" entity framework I would just assign a new EntityKey.. but Im not quite sure of how to do this using code first.. I also noticed that some people has an extra property called xxxxId for the entity they want to create a reference between.. and then simply assign a value to the xxxxId property which some how magically creates the reference between the entities.. and I guess this works fine for a one to one or a one to many relationship.. but I guess that doesnt work for a many to many relationship..or?

反正..这是我的GenresModel：

Anyway.. this is my GenresModel:

public class GenreModel : IModel
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public List<AlbumModel> Albums { get; set; }
}

这是我尝试过..但是这不会创造relationship..it只会简单地在我的数据库创建一个额外的实体/行..

And this is what I tried before.. but this wont create the relationship..it will only simply create an additional entity/row in my database..

var artistRepository = new ArtistRepository();
        var genresRepository = new GenreRepository();

        #region Lordi
        context.Albums.Add
            (
                new AlbumModel
                {
                    Artist = artistRepository.GetByName("Lordi"),
                    ArtUrl = "http://upload.wikimedia.org/wikipedia/en/8/8f/The_Monster_Show.jpg",
                    Genres = new List<GenreModel> { genresRepository.GetByName("Rock"), genresRepository.GetByName("Hard rock") },
                    Id = Guid.NewGuid(),
                    Price = 3,
                    Title = "The Monster Show",
                }
            );
        context.Albums.Add
            (
                new AlbumModel
                {
                    Artist = artistRepository.GetByName("Lordi"),
                    ArtUrl = "http://www.nuclearblast.de/static/articles/157/157892.jpg/1000x1000.jpg",
                    Genres = new List<GenreModel> { genresRepository.GetByName("Rock"), genresRepository.GetByName("Hard rock") },
                    Id = Guid.NewGuid(),
                    Price = 10,
                    Title = "Zombilation - The Greatest Cuts",
                }
            );
        #endregion

...并备案...没有我不听洛尔迪:) ..只是虚拟数据..和一些奇怪的怪异原因洛尔迪是排在脑海的第一个乐队。

...and for the record... no I dont listen to Lordi :).. just dummy data.. and for some wierd spooky reason Lordi was the first band that came in mind..

在此先感谢！

推荐答案

指定的集合属性为你做会自动创建一个多到很多所谓的联表 GenreModelAlbumModels 。

Specifying those collection properties as you have done will automatically create a many-to-many linking table called GenreModelAlbumModels.

不过，我怀疑你的资料库是明知有关系preventing EF。如果你不加载在同一个数据上下文中的实体GenreModel，它可能不知道，它们之间的联系。作为一个例子，这个code工作：

However, I suspect that your repository is preventing EF from knowing that there is a relationship. If you're not loading the GenreModel entities in the same data context, it may not know that there is a link between them. As an example, this code works:

    using (var context = new DataContext())
    {
        #region Lordi

        context.Albums.Add
            (
                new AlbumModel
                {
                    ArtUrl = "http://upload.wikimedia.org/wikipedia/en/8/8f/The_Monster_Show.jpg",
                    Genres = new List<GenreModel> { context.Genres.First(i => i.Name == "Rock"), context.Genres.First(i => i.Name == "Hard Rock") },
                    Id = Guid.NewGuid(),
                    Price = 3,
                    Title = "The Monster Show",
                }
            );

        context.SaveChanges();

        #endregion
    }

该GenreModels连接到我们正在加入到AlbumModels同样的背景下，使EF知道有实体之间的关系。

The GenreModels are connected to the same context that we're adding the AlbumModels to, so EF knows that there is a relationship between the entities.

要确保它的正常工作，请在您的数据库链接该表。它会从你在code被隐藏。

To make sure it's working properly, look for that linking table in your DB. It will be hidden from you in the code.

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