Partial class to override SaveChanges of DbContext and use it for creating audit trail

CustomDbContext.cs

public partial class CustomDbContext: DbContext
    {
        public override int SaveChanges()
        {
            // Get all Added/Deleted/Modified entities (not Unmodified or Detached)
            //you can get updated and deleted in same collection. I am doing so for ease of purpose
            //getting added entries in different collection to fetch their generated ids and then log them
            var addedEntries = ChangeTracker.Entries().Where(e => e.State == EntityState.Added).ToList();
            var updatedEntries = ChangeTracker.Entries().Where(e => e.State == EntityState.Modified).ToList();
            var deletedEntries = ChangeTracker.Entries().Where(e => e.State == EntityState.Deleted).ToList();

            foreach (var entry in updatedEntries)
            {
                ApplyAuditLog(entry);
            }

            foreach (var entry in deletedEntries)
            {
                ApplyAuditLog(entry);
            }

            int changes = base.SaveChanges();
            foreach (var entry in addedEntries)
            {
                ApplyAuditLog(entry);
            }

            base.SaveChanges();
            return changes;
        }

        /// <summary>
        /// code to enter values in audit table
        /// </summary>
        /// <param name="entry"></param>
        /// <param name="auditType"></param>
        private void ApplyAuditLog(DbEntityEntry entry)
        {
            //get table name of entry
            string tableName = GetTableName(entry);

            //exlude audit table from getting audited
            if (!tableName.Equals("Audit", StringComparison.OrdinalIgnoreCase))
            {

                //code to get primary key (id) of object which is updated
                var objectStateEntry = ((IObjectContextAdapter)this).ObjectContext.ObjectStateManager.GetObjectStateEntry(entry.Entity);
                int primaryKeyOfEntity = (int)objectStateEntry.EntityKey.EntityKeyValues[0].Value;

                DateTime currentDateTime = DateTime.Now;

                //code to convert the updated/added/deleted entry to json using newtonsoft json nuget package
                string serializedJson = JsonConvert.SerializeObject(entry.CurrentValues.ToObject(), Formatting.Indented, new JsonSerializerSettings
                {
                    //below code ignores the circular references. Main reason XML is not used as this was so wasy in JSON
                    ReferenceLoopHandling = ReferenceLoopHandling.Ignore
                });

                Audit auditTrail = new Audit()
                {
                    TimeStamp = currentDateTime,
                    AuthenticatedUser = {/* code to log authenticated user */ },
                    LinkedID = primaryKeyOfEntity,
                    AuditType = {/*create/update/delete/or read. Write your own logic here */ },
                    TableName = tableName,
                    NewValue = serializedJson
                };

                //you can write code here to generated checksum using algo like SHA1, MD5 and then update it in audit trail
                //string checksumValue = GetChecksumValueFromTrail(auditTrail);

                //write code to add entry in audit table here like below
                //Audit.Add(auditTrail);
            }
        }

        /// <summary>
        /// method to fetch table name of updated entity
        /// </summary>
        /// <param name="dbEntityEntry"></param>
        /// <returns></returns>
        private string GetTableName(DbEntityEntry dbEntityEntry)
        {
            ObjectContext objectContext = ((IObjectContextAdapter)this).ObjectContext;
            Type entityType = dbEntityEntry.Entity.GetType();

            if (entityType.BaseType != null && entityType.Namespace == "System.Data.Entity.DynamicProxies")
                entityType = entityType.BaseType;

            string entityTypeName = entityType.Name;

            EntityContainer container =
                objectContext.MetadataWorkspace.GetEntityContainer(objectContext.DefaultContainerName, DataSpace.CSpace);
            string entitySetName = (from meta in container.BaseEntitySets
                                    where meta.ElementType.Name == entityTypeName
                                    select meta.Name).First();
            return entitySetName;
        }
    }

hello, i know this was 5 years ago but can I ask why you base.SaveChanges(); twice?

Hello, As far as I remember, I wanted to get the number of rows modified/deleted for some logic in the code. Hence called it twice to keep added rows and modified rows separate.