使用不同的外键指定一对多关系

Question

Not sure if the title is good enough, but I'm going to try to explain the problem I'm encountering. For the record, I'm very new to Code-First and Fluent API, and this is the first production project I'm using them in.

Basically, the web-app I'm trying to create is multi-lingual, and I decided to have a table with the following fields (I added comments to explain what I'm trying to achieve):

public class Content
{
    [Key]
    // Required Key.
    public int Id { get; set; }

    [Required]
    // Language (another class that stores culture and other culture specific info).
    public Language Language { get; set; }

    [Required]
    // Text for the current field.
    [Column(TypeName = "ntext")]
    public string Text { get; set; }

    [Required]
    // The field Id, this stores what field the text above relates to.
    // So if I have a field "Welcome", and the website has 5 languages, I'll have 5 entries with the same GUID
    // but with different text and different language.
    public virtual Guid FieldId { get; set; }
}

I have been trying many solutions, but I haven't managed to create what I want. My latest one is:

    [Key]
    public int Id { get; set; }

    [Required]
    [Key]
    public Guid TitleId { get; set; }
    [Required]
    [Column("TitleId")]
    public virtual ICollection<Content> Title { get; set; }

    [Required]
    public decimal Value { get; set; }

    [Required]
    [Key]
    public Guid DescriptionId { get; set; }
    [Required]
    public virtual ICollection<Content> Description { get; set; }

and this in context (not sure if it makes sense):

modelBuilder.Entity<Winning>()
    .HasMany(x => x.Description)
    .WithRequired()
    .Map(x =>
    {
        x.MapKey("DescriptionId", "FieldId")
            .MapKey("TitleId", "FieldId");
    });

Basically what I want is that when I load the object above, through that GUID, I get a list of relating text (preferably just one, as I'd filter by culture), the table Content will be used by other object so a foreign key within Content does not solve my issue.

Answer 1

Hm.. where to start. :)

you don't need to have the ID of the Object and the Object both mapped. In fact EF won't like this.

Just something like this will get you the code first mapping that you want:

[Required] [Key] public Guid DescriptionId { get; set; }

[Required]
public virtual ICollection<Content> Description { get; set; }

The fluent mapping you are trying to use is for many to many relationships. You only need to specify fluent mappings if the code first migration doesn't work, or if you want to specify your own column or table names. Once you remove your double mappings you probably won't need to specify anything special in fluent. Code first will just figure out what the column need to be and create them for you (unless you are working with an existing DB). IF you find you still need fluent make sure you are using the correct mapping.

Lastly I don't think you can solve your problem using mappings. Map your entities so that the relate together. Not sure what your second entity is named but here goes...

Winning has a collection of Titles and Descriptions? Then when you are displaying this information on a page you just need to use some code/logic in your controller to decide which title and description you will use in your view based on the current conditions of your application. Maybe you have something in your controller method to say what language you need etc.

Hope that gets you back on the right track.