Entity Framework not adding multiple objects - asp.net-core

Question

Im trying to add some dummy content into my database. I have a sample object called "obj", and I'm using a for loop to insert data like the code below:
public async Task<Post> Add(Post obj)
{
if (db != null)
{
obj.Id = 0;
for (int i = 0; i < 100; i++)
{
await db.Post.AddAsync(obj);
}
await db.SaveChangesAsync();
return obj;
}
return null;
}
However, it does add only 1 record into database, could you please explain what's wrong here?

Answer 1

Can you create object of post inside the loop and try again?
for (int i = 0; i < 100; i++)
{
Post obj = new Post();
await db.Post.AddAsync(obj);
}

Answer 2

If you run the below commands before calling saved changes you can see what changes EF Core has queued up.
var post = new Post();
for (int i = 0; i < 10; i++)
{
await db.Posts.AddAsync(dev);
}
db.ChangeTracker.DetectChanges();
Debug.WriteLine(db.ChangeTracker.DebugView.LongView);
await db.SaveChangesAsync();
This will write to Debug that one post is currently being tracked.
for (int i = 0; i < 10; i++)
{
var post = new Post();
await db.Posts.AddAsync(dev);
}
db.ChangeTracker.DetectChanges();
Debug.WriteLine(db.ChangeTracker.DebugView.LongView);
await db.SaveChangesAsync();
This will right to the Debug window the 10 posts are currently being tracked.
In your code when you AddAsync(obj), obj isn't a new object and EF Core is already tracking obj.
Moving Post obj = new Post() into the loop creates a new object for EF Core to track. If these objects aren't being added to the DB my guess would be that they don't meet a requirement for the Post model.
Either way playing around with
db.ChangeTracker.DetectChanges();
Debug.WriteLine(db.ChangeTracker.DebugView.LongView);
should help you be able to track down exactly what's going on.
I do hope you find this information helpful :)

Answer 3

You can try to use AddRange.
public async Task<Post> Add(Post obj)
{
if (db != null)
{
List<Post>=new List<Post>();
obj.Id = 0;
for (int i = 0; i < 100; i++)
{
l.Add(obj);
}
await db.Post.AddRangeAsync(l);
await db.SaveChangesAsync();
return obj;
}
return null;
}