Automatically instantiate OneToOne Relationship in EntityFramework (in Combination with WPF)

Question

I have two Classes:

Book
MultilingualString (Which has many Translations, but thats not important for this example)

My goal is to automatically Instantiate the Reference from Book to MultilingualString (Book.Description).

This is in a relatively complicated application so I reduced it down to the necessary code. The following example shows how my application is interacting with EF:

static void Main(string[] args)
{
    using(var model = new ModelCFContext())
    {
        // Done by a generic ViewModel
        var book = model.Set<Book>().Create();

        // Currently I am instantiating book.Description inside the ViewModel (of Book in this case).
        // Is there a better way?
        book.Description = model.MultilingualStrings.Create();

        // Set by TextBox-Binding
        book.Description.TextDefault = "TestDefault3";

        // Done by a generic ViewModel
        Insert(model, book);
    }

    using (var model = new ModelCFContext())
    {
        OutputFirstBook(model);
    }

    Console.ReadKey();
}

private static void OutputFirstBook(ModelCFContext model)
{
    var spez = model.Books.FirstOrDefault();
    Console.WriteLine(spez.Description.TextDefault);
}

private static void Insert<T>(ModelCFContext model, T book) where T : class
{
    model.Set<T>().Add(book);

    model.SaveChanges();
}

Usually I would instantiate such a reference in the constructor of Book. But that will not work because EntityFramework will not inject the Proxy (when loading the data from the database).

Book-Class:

[Table("Book")]
public partial class Book
{
    public Book()
    {
        //Description = new MultilingualString();
    }

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

    [Required]
    public virtual MultilingualString Description { get; set; }


}

MultilingualString-Class:

[Table("MultilingualString")]
public partial class MultilingualString
{
    public MultilingualString()
    {
        Translations = new ObservableCollection<Translation>();
    }

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

    public string TextDefault { get; set; }

    public virtual ObservableCollection<Translation> Translations { get; set; }
}

I am currently instantiating book.Description in the ViewModel of Book. Is there a nicer way to do that?

score 0 · Accepted Answer · answered Mar 27 '20 at 11:16

Found a solution, with which I will currently stick with.

I use BaseEntity:

public class BaseEntity
{
    public virtual void InitializeEntity() { }
}

Which I override in Book:

public override void InitializeEntity()
{
    if(Description == null)
        Description = new MultilingualString();
}

And then I can call InitializeEntity() in my generic ViewModel (where TEntity : BaseEntity) after I create or load an Entity.

var entity = model.Set<TEntity>().Create();
entity.InitializeEntity();

var entity = model.Set<TEntity>().Find(keys);
entity.InitializeEntity();

The reason this works is, because Description will have been loaded and I can check whether it is null or not.

Automatically instantiate OneToOne Relationship in EntityFramework (in Combination with WPF)

1 Answers1