HiLoGenerator生成id

using System.Linq;

namespace Product.Host
{
    public class HiLoGenerator
    {
        private const int HiLoIncrement = ;
        private int _sequenceId = -;
        private int _remainningLoIds = ;
        private object SequenceLock = new object();

        public int GetNextSequenceValue(ProductDbContext db)
        {
            lock (SequenceLock)
            {
                if (_remainningLoIds == )
                {
                    var rawQuery = db.Database.SqlQuery<long>("SELECT NEXT VALUE FOR Product_HiLo;");
                    _sequenceId = (int)rawQuery.Single();
                    _remainningLoIds = HiLoIncrement - ;
                    return _sequenceId;
                }
                else
                {
                    _remainningLoIds--;
                    return ++_sequenceId;
                }
            }
        }
    }
}

sql

CREATE SEQUENCE [dbo].[Product_HiLo]
 AS [bigint]
 START WITH
 INCREMENT BY
 MINVALUE -
 MAXVALUE
 CACHE