public void ModifyInstsAndChannels(ChannelEditRequest request)
{
    var merchantInsts = _dbfd.MerchantInst.Where(mi => mi.MerchantId == request.MerchantId).ToList();
    var query = (from miNew in request.MerchantInsts
                 join mi in merchantInsts
                     on miNew.InstCode equals mi.InstCode into g
                 from miOld in g.DefaultIfEmpty()
                 select new { miNew, miOld });
    var list = query.ToList();
    foreach (var pair in list)
    {
        var miNew = pair.miNew;
        var miOld = pair.miOld;

        if (miOld == null)
        {
            if (!miNew.Checked) continue;

            var mi = miNew;
            mi.Guid = Guid.NewGuid().ToString("N");
            mi.CreateTime = DateTime.Now;
            mi.OptUser = request.OptUser;
            mi.MerchantChannels = miNew.MerchantChannels.Where(mc => mc.Checked).Select(mc =>
            {
                mc.CreateTime = DateTime.Now;
                mc.OptUser = request.OptUser;
                mc.Guid = Guid.NewGuid().ToString("N");
                return mc;
            }).ToList();
            _dbfd.MerchantInst.Add(mi);
        }
        else if (miNew.Checked)
        {
            miOld.InstMerchantId = miNew.InstMerchantId;
            miOld.InstKey = miNew.InstKey;
            miOld.InstShowName = miNew.InstShowName;
            miOld.Checked = miNew.Checked;
            miOld.UpdateTime = DateTime.Now;
            miOld.OptUser = request.OptUser;
            miOld.Guid = Guid.NewGuid().ToString("N");

            ModifyMerchantChannels(request.MerchantId, miNew.InstCode, request.OptUser, miNew.MerchantChannels);
        }
        else if (miOld.Checked && !miNew.Checked)
        {
            miOld.Checked = false;
            miOld.OptUser = request.OptUser;
            miOld.UpdateTime = DateTime.Now;
            miOld.Guid = Guid.NewGuid().ToString("N");
        }
    }

    _dbfd.SaveChanges();
}

private void ModifyMerchantChannels(string merchantId, string instCode, string optUser, IEnumerable<MerchantChannel> newMerchantChannels)
{
    var oldMerchantChannels = _dbfd.MerchantChannel.Where(mc => mc.MerchantId == merchantId && mc.InstCode == instCode).ToList();
    var query = (from mcNew in newMerchantChannels
                 join mcOld in oldMerchantChannels
                     on mcNew.ChannelId equals mcOld.ChannelId into g
                 from mcOld in g.DefaultIfEmpty()
                 select new { mcNew, mcOld });

    var list = query.ToList();
    foreach (var pair in list)
    {
        var mcOld = pair.mcOld;
        var mcNew = pair.mcNew;

        if (mcOld == null)
        {
            if (!mcNew.Checked) continue;

            MerchantChannel mc = mcNew;
            mc.CreateTime = DateTime.Now;
            mc.OptUser = optUser;
            mc.Guid = Guid.NewGuid().ToString("N");
            _dbfd.MerchantChannel.Add(mc);
        }
        else if (mcNew.Checked)
        {
            mcOld.InstCode = mcNew.InstCode;
            mcOld.ApplyingType = mcNew.ApplyingType;
            mcOld.Fee = mcNew.Fee;
            mcOld.Checked = mcNew.Checked;
            mcOld.UpdateTime = DateTime.Now;
            mcOld.OptUser = optUser;
            mcOld.Guid = Guid.NewGuid().ToString("N");
        }
        else if (mcOld.Checked && !mcNew.Checked)
        {
            mcOld.Checked = false;
            mcOld.UpdateTime = DateTime.Now;
            mcOld.OptUser = optUser;
            mcOld.Guid = Guid.NewGuid().ToString("N");
        }
    }
}