Delete trigger for audit table - sql-server

Question

I'm working on a web application that executes CRUD operations on some table in a SQL Server database. There will be a logged user in the application executing these operations.
(By the way, I'm using Entity Framework)
Let's say table is
MyTable
MyTableId
SomeColumn
LastModifiedUserId
LastModifiedDate
And I a have an audit table like
MyTableHistory
MyTableHistoryId
MyTableId
SomeColumn
ActionType --ins/upd/del
ActionUserId
ActioDate
And I'm using triggers to insert data on the audit table.
Inserts and updates are easy by consulting the Inserted and Updated tables to find the userid who modified the record.
But what about deletes? Any idea how I might get that info?

Answer 1

There is no such thing as updated table. The two pseudo tables available in DML triggers are inserted and deleted. In the case of insert table deleted is empty, in the case of delete table inserted is empty, in the case of update both tables are populated.
You can create three separate triggers for each action (to distinguish ActionType) or try to combine all in one trigger.
Note: take into account multiple row actions.

Answer 2

Assuming you are using EF to add the information about which user is updating records, the easiest way to capture that information is to have EF perform a 2-step process (UPDATE, DELETE) on the data you wish to delete. You will then need to interpret the two audit rows as part of the same operation.
There is a much more involved solution that "might" work, but I have not tested it. There is more information available below if you wish to explore it.
Blog describing the solution
Stack Overflow post of someone trying it
Another option altogether is to abandon trigger auditing (which is problematic for this very reason) and use Entity Framework instead. Below is an example of how one might accomplish this by overriding the SaveChanges method:
public virtual IEnumerable<System.Data.Entity.Infrastructure.DbEntityEntry> ChangedEntries()
{
return ChangeTracker.Entries().Where(x =>
x.State == EntityState.Added ||
x.State == EntityState.Deleted ||
x.State == EntityState.Modified);
}
public virtual int SaveChanges(string userName)
{
var changes = ChangedEntries();
foreach (var entry in changes)
{
var eventType = entry.State == EntityState.Added ? "A" : entry.State == EntityState.Deleted ? "D" : "U";
var entityType = ObjectContext.GetObjectType(entry.Entity.GetType()).Name;
var oldValues = entry.State == EntityState.Added ? null : JsonConvert.SerializeObject(entry.OriginalValues.ToObject());
var newValues = entry.State == EntityState.Deleted ? null : JsonConvert.SerializeObject(entry.CurrentValues.ToObject());
oldValues = oldValues?.Substring(0, Math.Min(oldValues.Length, 4000));
newValues = newValues?.Substring(0, Math.Min(newValues.Length, 4000));
AuditItems.Add(
new AuditItem
{
EventTime = DateTime.Now,
UserName = userName,
EntityType = entityType,
EventType = eventType,
OldValues = oldValues,
NewValues = newValues
}
);
}
return base.SaveChanges();
}