Is possible to avoid rewriting properties mapping the "one-to-many" relationship? - asp.net-mvc

Question

I am developing a blog application in ASP.NET MVC and I have doubt whether my solution of updating some related classes is fully correct.
I have a class representing texts:
public partial class Text
{
public long ID { get; set; }
public string Title { get; set; }
...
public virtual ICollection<Tag> Tags { get; set; }
}
and tags:
public partial class Tag
{
public long ID { get; set; }
public string Name { get; set; }
public virtual ICollection<Text> Texts { get; set; }
}
When I'm editing a texts, the TextEditorViewModel is being passed:
public class TextEditorViewModel
{
public long ID { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public IEnumerable<TagEditorViewModel> Tags { get; set; }
}
TagEditorViewModel is:
public class TagEditorViewModel
{
public long ID { get; set; }
public string Name { get; set; }
public bool IsInText { get; set; }
}
In the view I'm checking appropiate tags (this is reflected by IsInText property) and this works fine and correct data is being passed back to the controller.
Here is my code for the repository on which controller is working:
Text OriginalText = Mapper.Map<Text>(Text);
IEnumerable<long> tags = OriginalText.Tags.Select(tag => tag.ID);
ICollection<Tag> tagobj = context.Tags.Where(tag => tags.Contains(tag.ID)).ToList();
OriginalText.Tags = tagobj;
Text is object of TextEditorViewModel which is passed back on post. I'm using mapper to bind only primitive types and I'm rewriting all collection and reference types (as seen above), only tags marked as not in the text are filtered out. Is there any simpler way of managing the tags instead of quering the database and rewriting them?

Answer 1

You can attach the tags manually to the context instead of reloading them from the database because you have the ID of the tags which is sufficient to create/update a relationship:
Text OriginalText = Mapper.Map<Text>(Text);
foreach (var tag in OriginalText.Tags)
context.Tags.Attach(tag);
context.Texts.Add(OriginalText);
context.SaveChanges();
(I've taken the last two lines from your comment.)
Even though the properties in the different tags don't have the values from the database (except the ID) it will work because EF only needs the correct tag ID to create the relationship.