petapoco IsNew

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// Check if a poco represents a new record
        public bool IsNew(string primaryKeyName, object poco)
        {
            var pd = PocoData.ForObject(poco, primaryKeyName);
            object pk;
            PocoColumn pc;
            if (pd.Columns.TryGetValue(primaryKeyName, out pc))
            {
                pk = pc.GetValue(poco);
            }
#if !PETAPOCO_NO_DYNAMIC
            else if (poco.GetType() == typeof(System.Dynamic.ExpandoObject))
            {
                return true;
            }
#endif
            else if (primaryKeyName.Contains(","))
            {
                return primaryKeyName.Split(‘,‘)
                    .Select(pkPart => GetValue(pkPart, poco))
                    .Any(pkValue => IsDefaultOrNull(pkValue));
            }
            else
            {
                pk = GetValue(primaryKeyName, poco);
            }

            return IsDefaultOrNull(pk);
        }

        private static object GetValue(string primaryKeyName, object poco)
        {
            object pk;
            var pi = poco.GetType().GetProperty(primaryKeyName);
            if (pi == null)
                throw new ArgumentException(
                    string.Format("The object doesn‘t have a property matching the primary key column name ‘{0}‘",
                                  primaryKeyName));
            pk = pi.GetValue(poco, null);
            return pk;
        }

        private static bool IsDefaultOrNull(object pk)
        {
            if (pk == null)
                return true;

            var type = pk.GetType();

            if (type.IsValueType)
            {
                // Common primary key types
                if (type == typeof(long))
                    return (long)pk == default(long);
                else if (type == typeof(ulong))
                    return (ulong)pk == default(ulong);
                else if (type == typeof(int))
                    return (int)pk == default(int);
                else if (type == typeof(uint))
                    return (uint)pk == default(uint);
                else if (type == typeof(Guid))
                    return (Guid)pk == default(Guid);

                // Create a default instance and compare
                return pk == Activator.CreateInstance(pk.GetType());
            }
            else
            {
                return pk == null;
            }
        }

petapoco IsNew

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原文地址：http://www.cnblogs.com/zwei1121/p/5201678.html