C#实体框架——添加新记录

Question

Is this code correct to add a record with a relationship Id? If i enter the Id directly, i get the following error

Cannot implicitly convert type 'int' to 'Project.Models.Database.ArticleDatabase'

Is this code below the correct way?

var newArticle = new Articles();

newArticle.Artname = addarticle.Articlename;

//NOT WORKING
// newArticle.Artdatabase = addarticle.ArticlegroupId

//WORKING, SEEMS WRONG
newArticle.Artdatabase = _context.ArticleDatabase.SingleOrDefault(c => c.Id == addarticle.ArticlegroupId);


newArticle.Articleaadddate = DateTime.Now;
newArticle.Articlelastedit = DateTime.Now;
newArticle.Artstatus = 3;

_context.Articles.Add(newArticle);
_context.SaveChanges();

Answer 1

//NOT WORKING

// newArticle.Artdatabase = addarticle.ArticlegroupId

That's because you're trying to set the ArticlegroupId (which seems to be an int ) to a property that seems to be of type ArticleDatabase .

I assume your model looks something like this:

public class Articles
{
    public string Artname { get; set; }

    [ForeignKey("ArtdatabaseId")]
    public virtual ArticleDataBase Artdatabase { get; set; }

    // For alternative 2 you'll need this.
    public int ArtdatabaseId { get; set; }
}

Alternative 1. Use the navigation property. When using the navigation property you need to attach it.

var newArticle = new Articles();

newArticle.Artname = addarticle.Articlename;

// Create the entity and attach it.
var artDataBase = new ArticleDataBase
{
    Id = addarticle.ArticlegroupId
};
_context.ArticleDatabase.Attach(artDataBase);

newArticle.Artdatabase = artDataBase;
newArticle.Articleaadddate = DateTime.Now;
newArticle.Articlelastedit = DateTime.Now;
newArticle.Artstatus = 3;

_context.Articles.Add(newArticle);
_context.SaveChanges();

Alternative 2. Use the foreign key-property. When using this option you need to explicitly define the foreign key in your model.

var newArticle = new Articles();

newArticle.Artname = addarticle.Articlename;
// Note that I'm using ArtdatabaseId and not Artdatabase.
newArticle.ArtdatabaseId = addarticle.ArticlegroupId

newArticle.Articleaadddate = DateTime.Now;
newArticle.Articlelastedit = DateTime.Now;
newArticle.Artstatus = 3;

_context.Articles.Add(newArticle);
_context.SaveChanges();

Take a look at this article for defining foreign keys with fluent instead.

modelBuilder.Entity<Post>().HasRequired(p => p.Blog) 
                .WithMany(b => b.Posts) 
                .HasForeignKey(p => p.FKBlogId);