[Question] DateTimeOffset? protobuf serialization/deserialization in ASP Core

[odysseus1973]

Hi!

After some investigation and reading posts on SO I found two ways to serialize DateTimeOffset?

1. Shim properties (working, but does not fit in my case)

2. Surrogates. Not working in my case In my StartUp file I use

   RuntimeTypeModel.Default.Add(typeof(DateTimeOffset),false).SetSurrogate(typeof(DateTimeOffsetSurrogate));
   RuntimeTypeModel.Default.Add(typeof(DateTimeOffset?),false).SetSurrogate(typeof(DateTimeOffsetSurrogate));

   My surrogate class

   [ProtoContract]
   public class DateTimeOffsetSurrogate
   {
       [ProtoMember(1)]
       public string Date { get; set; }
   
       //public static implicit operator DateTimeOffsetSurrogate(DateTimeOffset? value)
       //{
       //    return (value.HasValue) ? new DateTimeOffsetSurrogate { Date = value.Value.ToString("o") } : new DateTimeOffsetSurrogate { Date = null };
       //}
   
       //public static implicit operator DateTimeOffset? (DateTimeOffsetSurrogate value)
       //{
       //    DateTimeOffset? result = null;
       //    if (DateTimeOffset.TryParse(value.Date, out DateTimeOffset date))
       //    {
       //        result = date;
       //    }
       //    return result;
       //}
   
       public static implicit operator DateTimeOffsetSurrogate(DateTimeOffset value)
       {
           return (value != null) ? new DateTimeOffsetSurrogate { Date = value.ToString("o") } : new DateTimeOffsetSurrogate { Date = null };
       }
   
       public static implicit operator DateTimeOffset(DateTimeOffsetSurrogate value)
       {
           // DateTimeOffset? result = null;
           // if (
           DateTimeOffset.TryParse(value.Date, out DateTimeOffset date);
           //{
           //    result = date;
           //}
           return date;
       }
   }

   My serialized class

   [ProtoContract]
   public class StocksDto
   {
       [JsonIgnore]
       public Guid? StoreId { get; set; }
       [Required]
       public DateTimeOffset? Date { get; set; }
       [JsonIgnore]
       public DateTime DateUtc { get { return Date.HasValue ? Date.Value.UtcDateTime : DateTime.MinValue; } }
       [JsonIgnore]
       public double TimeZoneOffset { get { return Date.HasValue ? Date.Value.Offset.TotalMinutes : 0; } }
       [ProtoMember(1)]
       [Required]
       public bool? Full { get; set; }
       [HasElements(ErrorMessage = "The field Stocks must contain non-empty array of elements")]
       [ProtoMember(2)]
       public IEnumerable<Stock> Stocks { get; set; }
   }

   When I try serialize/deserialize StocksDto, Date property return no value (null). As I can see implicit operator in surrogate does not called. How to use surrogate for DateTimeOffset? in my case?

[rushfrisby]

Your surrogate should be

using System;
using System.Runtime.Serialization;

namespace ProtobufNetTest
{
    [DataContract(Name = nameof(DateTimeOffset))]
    public class DateTimeOffsetSurrogate
    {
        [DataMember(Order = 1)]
        public long? Value { get; set; }

        public static implicit operator DateTimeOffset(DateTimeOffsetSurrogate surrogate)
        {
            return DateTimeOffset.FromUnixTimeMilliseconds(surrogate.Value.Value);
        }

        public static implicit operator DateTimeOffset?(DateTimeOffsetSurrogate surrogate)
        {
            return surrogate != null ? DateTimeOffset.FromUnixTimeMilliseconds(surrogate.Value.Value) : (DateTimeOffset?)null;
        }

        public static implicit operator DateTimeOffsetSurrogate(DateTimeOffset source)
        {
            return new DateTimeOffsetSurrogate
            {
                Value = source.ToUnixTimeMilliseconds()
            };
        }

        public static implicit operator DateTimeOffsetSurrogate(DateTimeOffset? source)
        {
            return new DateTimeOffsetSurrogate
            {
                Value = source?.ToUnixTimeMilliseconds()
            };
        }
    }
}

[odysseus1973]

Thanks! I will try it, but why surrogate can't use string and how to register surrogate correctly? When I was debugging I did not see that the surrogate was called, so i think my problem with surrogate registration.

[rushfrisby]

The way you registered surrogates is correct however your class has a DateTimeOffset? property and your surrogate has no operators for converting between the two. Your surrogate only has operators for DateTimeOffset which is a different type.

Sure you can serialize the value as a string. I used long and the unix time value because the output is smaller than the string representation and faster than converting to/from a string.

[odysseus1973]

Thanks for answer! I specifically did not delete the commented lines in code block in my question, I tried it, but without success. How does converting to UnixTime support the time zone?

[rushfrisby]

By definition it takes into account the time zone since unix time starts at 1/1/1970 00:00:00 (UTC)

[paraboxx]

The purpose of DateTimeOffset is to preserve TimeZone information so it's possible to see at white Offset the timestamp was generated. By convertig to unixtime this information is lost.