Question:
How do
you get the new ID of a record that you attach to a table in SQL Server using
EF Entity Framework?
Solution:
You
create a blank record from the appropriate MVC data model, fill it with new
values โโand default values.
Then
you add this to the EF.Table
And
then update the EF dbContext.
Then
the record has automatically assigned the new ID.
|
NoteModel
note= new NoteModel();
note.DtCreated
= DateTime.Now;
await
_dbContext.tbl_Notes.AddAsync(note); //IDNote:
0->-99999
await
_dbContext.SaveChangesAsync(); //IDNote:
-99999->16
newID =
note.IDNote;
|
Explanation:
At the
time of creating new record, the included ID is always 0.
|
NoteModel
note= new NoteModel();
//ID==0
|
Once
you get the data
If the
record is appended to Entity Framework dbContext, the record is internally set
to a temporary ID.
|
await _dbContext.tbl_Notes.AddAsync(note); //IDNote:
0->-99999
|
By
updating EF to SQL Server, the temporary number becomes a real ID, which is
automatically incremented by SQL Server for incremental identity.
|
await
_dbContext.SaveChangesAsync(); //IDNote:
-99999->16
|
Since
the dataset is still local in memory, you can read and process it directly from
the dataset
In the debugger
Record
is added to EF table.
Before appending, the ID = 0
After dbContext.tbl.Add (recordset)
After
attaching to the EF dbContext table, the ID is a negative number of type long
After
performing dbContext.SaveChanges (), the ID becomes the correct ID of the SQL
Server
Complete c # code example
Asp.Net Core 2 MVC
|
NoteModel
note;
if
(IDNote==0)
{
note =
_dbContext.tbl_Notes.SingleOrDefault(n => n.IDUser == IDCurrent_User
&& n.IsDraft==true);
if (note == null)
{
note = new
NoteModel();
note.IsDraft = true;
note.DtCreated = DateTime.Now;
note.IDUser = IDCurrent_User;
note.Title = "#images";
note.sumImages = 0;
note.DtEdit = DateTime.Now;
//<
save >
await
_dbContext.tbl_Notes.AddAsync(note); //IDNote:
0->-99999
await
_dbContext.SaveChangesAsync(); //IDNote:
-99999->16
//</
save >
//< new
ID >
IDNote = note.IDNote;
//Console.WriteLine("new
IDNote=" + note.IDNote);
//</
new ID >
}
else
{
//<
last draft >
IDNote = note.IDNote;
//</
last draft >
}
}
|