尝试使用Entity Framework Code First更新数据库

Question

I am trying to update a database entry using entity framework. The entities are as follows:

public partial class Test
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid identity { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
    public TestRef Colour { get; set; }
}

public class TestRef
{
    public int id { get; set; }
    public string favColor { get; set; }
}

and the edit ActionResult in the relevant Controller is as follows:

public ActionResult Edit([Bind(Include = "identity,Name,Age,Colour")] Test test)
{
    if (ModelState.IsValid)
    {
        test.Colour = db.TestRefs.Find(test.Colour.id);
        db.Tests.Attach(test);
        db.Entry(test).State = EntityState.Modified;
        db.SaveChanges();
        return RedirectToAction("Index");
    }
    return View(test);
}

So here, Edit seems to work for all the properties in Test except for Colour (in that all the other properties get updated, but Colour remains as it was before, with no change). I am assuming this is because it is an association, but I can't for the life of me figure out why.

Answer 1

First, tell EF that TestRef have a key:

public class TestRef
{
    [Key] /* <--- */
    /*[DatabaseGenerated( ??? )] Does value generated by database? */
    public int id { get; set; }
    public string favColor { get; set; }
}

Second, make reference be a foreign key:

public partial class Test
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid identity { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }

    [ForeignKey("TestRefID")]  /* <--- */
    public TestRef Colour { get; set; }
}

Name TestRefID in code above is just example. Put there name of FK column from your database. You do have FK column in database for this relation, isn't it?

Also, if you need lazy loading, make Colour property virtual :

...
    [ForeignKey("TestRefID")]
    public virtual TestRef Colour { get; set; }
...

EF will make a direved type and for all virtual reference properties it will implement lazy-loading logic. It's default behavior until you disable it in db context settings:

yourDataContext.ContextOptions.LazyLoadingEnabled = false;

By the way, it's not a good idea to use GUID as primary key. Look here for cons and pros.