Why Can't I Get the Scoped Identity From EF After a Record is Saved?

I have this code that successfully creates a new entry in my Posts table but for some reason the Postid is null even though I don't try to access it until after the new record is created.

public async Task < IActionResult > OnPostAsync() {
if (!ModelState.IsValid) {
return Page();
}
_context.Posts.Add(Posts);
await _context.SaveChangesAsync();
int postid = Posts.Postid;
string targeturl = linkgenerator.postlink(Posts.Postid, Posts.Title);
return RedirectToPage(targeturl);
}

According to this tutorial all I need to do to access a newly created primary key is to type the name of the table followed by a "." and the name of the column https://www.entityframeworktutorial.net/faq/how-to-get-id-of-saved-entity-in-entity-framework.aspx but the above code returns a null value instead of the newly created Postid.

Most of the new record is created using a form on a Razor Page. The above code is from code behind on that page. After checking the database I can confirm that the new record is in fact created. Please word any response in a way that someone familiar with WebForms and not familiar at all with MVC can understand. I chose to convert my WebForms site to a .Net Core Razor Pages site because I was given the impression that it is closer to WebForms than any other modern option that uses the .Net Framework. So far it seems nothing like WebForms. Am I at least correct in believing that the OnPostAsync event in a Razor Page is the equivalent of the FormView_ItemInserting event in a WebForm?

UPDATE: Looking back it appears that I was never able to use the new primary key value in my WebForm until the SqlDataSource1_Inserted event. Is it possible to get the primary key during the same event on a Razor Page or do I need to add a second task that runs after the first one?

At first correct your naming convention.

let DBSet as Posts and your object as Post

your code should look like

public async Task < IActionResult > OnPostAsync() {
if (!ModelState.IsValid) {
return Page();
}
_context.Posts.Add(Post);
await _context.SaveChangesAsync();
int postid = Post.Postid;
string targeturl = linkgenerator.postlink(Post.Postid, Post.Title);
return RedirectToPage(targeturl);
}

Second , you misunderstood that you will get recently created entity's Id by TableName.Id , No rather you after

adding the object into DbSet collection Like _Context.Posts.Add(PostObj) , when you save changes on database by _Context.SaveChanges(); you can get the Id of that object only by PostObj.Postid

So , instead of table name use object name , obviously you can add a single object of Post type into the collection Posts and that object will give you its Id after successful save.

1 Reply

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Sachin Singh5y ago
At first correct your naming convention.
let DBSet as Posts and your object as Post
your code should look like
public async Task < IActionResult > OnPostAsync() {
  if (!ModelState.IsValid) {
    return Page();
  }
  _context.Posts.Add(Post);
  await _context.SaveChangesAsync();
  int postid = Post.Postid;
  string targeturl = linkgenerator.postlink(Post.Postid, Post.Title);
  return RedirectToPage(targeturl);
}
Second , you misunderstood that you will get recently created entity's Id by TableName.Id , No rather you after
adding the object into DbSet collection Like _Context.Posts.Add(PostObj) , when you save changes on database by _Context.SaveChanges(); you can get the Id of that object only by PostObj.Postid

So , instead of table name use object name , obviously you can add a single object of Post type into the collection Posts and that object will give you its Id after successful save.
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