Adding to or updating an entity in a foreach loop takes too long time before calling SaveChanges()?

问题

I have this method that saves an entity with its related items (many-to-many relationship),

private static void Save<T>(TbCommonHistoryLog log, List<T> lstDetails) where T : IHasSerial
{   
    foreach (var item in lstDetails.OrderBy(x => x.Serial))
    {
        var ser = SerializeObject(item);
        var record = oContext.TbHistoryLog_Lists.FirstOrDefault(x => x.ListObjectJson == ser);
        if (record == null) //add new list item
        {
            TbCommonHistoryLog_Lists listObject = new TbCommonHistoryLog_Lists()
            {
                ListObjectJson = SerializeObject(item)
            };
            var details = new TbCommonHistoryLogDetails { TbHistoryLog = log, TbHistoryLog_Lists = listObject };
            oContext.TbHistoryLogDetails.Add(details);
        }
        else //attach an existing list item
        {
            var o = oContext.TbHistoryLog_Lists.Find(record.Id);
            oContext.TbHistoryLog_Lists.Attach(o);
            var details = new TbCommonHistoryLogDetails { TbHistoryLog = log, TbHistoryLog_Lists = o };
            oContext.TbHistoryLogDetails.Add(details);
        }
    }
    oContext.BulkSaveChanges();
}

I have two tables: TbCommonHistoryLog, TbCommonHistoryLog_Lists, that are in many to many relationship, the joining table is TbCommonHistoryLogDetails, What I'm doing here is an auditing for master-detail models, all audits are serialized to JSON in DB, I save the head object in the TbCommonHistoryLog table, and every list item in the TbHistoryLog_Lists table, in the mthod above I check if the list item is already exists in the database or not to avoid duplicating. but this process takes more than 15 seconds which is a very long time, I can't figure out what am I doing wrong here.. please help?

回答1:

For every single item in collection you're querying database. My suggestion is to save records in var, then ask the variable if the item is in database.

var databaseRecords = oContext.TbHistoryLog_Lists.ToList();

Then in the loop:

var record = databaseRecords.FirstOrDefault(x => x.ListObjectJson == ser);

来源：https://stackoverflow.com/questions/46753598/adding-to-or-updating-an-entity-in-a-foreach-loop-takes-too-long-time-before-cal