Entity Framework Code First and SQL Server 2012 Sequences

Question

I was in the middle of implementing a database audit trail whereby CRUD operations performed through my controllers in my Web API project would serialize the old and new poc

Answer 1

Don't know if this might help you, but this is how I did my audit log trail using code first. The following is coded into a class inheriting from DbContext.

in my constructor I have the following

IObjectContextAdapter objectContextAdapter = (this as IObjectContextAdapter);
objectContextAdapter.ObjectContext.SavingChanges += SavingChanges;

This is my saving changes method wired up previously

void SavingChanges(object sender, EventArgs e) {
        Debug.Assert(sender != null, "Sender can't be null");
        Debug.Assert(sender is ObjectContext, "Sender not instance of ObjectContext");

        ObjectContext context = (sender as ObjectContext);
        IEnumerable modifiedEntities = context.ObjectStateManager.GetObjectStateEntries(EntityState.Modified);
        IEnumerable addedEntities = context.ObjectStateManager.GetObjectStateEntries(EntityState.Added);

        addedEntities.ToList().ForEach(a => {
            //Assign ids to objects that don't have
            if (a.Entity is IIdentity && (a.Entity as IIdentity).Id == Guid.Empty)
                (a.Entity as IIdentity).Id = Guid.NewGuid();

            this.Set().Add(AuditLogEntryFactory(a, _AddedEntry));
        });

        modifiedEntities.ToList().ForEach(m => {
            this.Set().Add(AuditLogEntryFactory(m, _ModifiedEntry));
        });
    }

And these are the methods used previosly to build up the audit log details

private AuditLogEntry AuditLogEntryFactory(ObjectStateEntry entry, string entryType) {
        AuditLogEntry auditLogEntry = new AuditLogEntry() {
            EntryDate = DateTime.Now,
            EntryType = entryType,
            Id = Guid.NewGuid(),
            NewValues = AuditLogEntryNewValues(entry),
            Table = entry.EntitySet.Name,
            UserId = _UserId
        };

        if (entryType == _ModifiedEntry) auditLogEntry.OriginalValues = AuditLogEntryOriginalValues(entry);

        return auditLogEntry;
    }

    /// 

    /// Creates a string of all modified properties for an entity.
    /// 
    private string AuditLogEntryOriginalValues(ObjectStateEntry entry) {
        StringBuilder stringBuilder = new StringBuilder();

        entry.GetModifiedProperties().ToList().ForEach(m => {
            stringBuilder.Append(String.Format("{0} = {1},", m, entry.OriginalValues[m]));
        });

        return stringBuilder.ToString();
    }

    /// 

    /// Creates a string of all modified properties' new values for an entity.
    /// 
    private string AuditLogEntryNewValues(ObjectStateEntry entry) {
        StringBuilder stringBuilder = new StringBuilder();

        for (int i = 0; i < entry.CurrentValues.FieldCount; i++) {
            stringBuilder.Append(String.Format("{0} = {1},",
                entry.CurrentValues.GetName(i), entry.CurrentValues.GetValue(i)));
        }

        return stringBuilder.ToString();
    }

Hopefully this might point you into a direction that might help you solve your problem.