jamescourtney
commented
3 years ago The reason I don't include any "sugar" types in FlatSharp is because the FlatBuffer format is still evolving, and I don't want to end up in a situation where I've done some custom implementation for something that ends up conflicting with a later standardized implementation in FlatBuffers proper. This is why I don't have dictionaries, timestamps, or other fun things! I did include ITypeModel as a way to extend FlatSharp, but you've discovered it's not for the faint of heart.
Anyway, here are my thoughts on how you can accomplish this.
Use protected properties
[FlatBufferTable]
public class MyNeatTable
{
public DateTimeOffset Timestamp
{
get => DateTimeOffset.FromUnixTimeSeconds(this.RawTimestamp);
set => this.RawTimestamp = value.ToUnixTimeSeconds();
}
[FlatBufferItem(0)]
protected virtual long RawTimestamp { get; set; }
}This approach isn't ideal because it forces you to do this indirection trick everywhere you want to use a timestamp. This also won't work if you're using an FBS file.
A timestamp class with operator overloads
[FlatBufferStruct]
public class MyTimestamp
{
[FlatBufferItem(0)]
public virtual long Value { get; set; }
public static implicit operator DateTimeOffset(this MyTimestamp ts) => DateTimeOffset.FromUnixTimeMilliseconds(ts.Value);
public static implicit operator MyTimestamp(this DatetimeOffset dto) => new MyTimestamp { Value = dto.ToUnixTimeMilliseconds() };
}This one will work in C# or using .fbs files, since FlatSharp generates partial classes for you. It will also allow you to write your code fluently because the operators are implicit.
Implementing ITypeModel / ITypeModelProvider
It's not as hard as it sounds, but it requires a little working knowledge of how FlatSharp operates internally. It's harder than it might need to be (perhaps I should come up with a way to alias certain types with well-known conversions). Anyway, here is a gist with some working code to accomplish this: https://gist.github.com/jamescourtney/5520f91f7bbb142301dafd7386eb5f39. The short version is that it works by wrapping the predefined LongTypeModel, and just modifying the inputs and outputs to the various serialization / get max size methods.
You could conceivably integrate this with the Flatsharp compiler, though I have not done that. Mainly because I assume anyone using an FBS file cares about cross-language compatibility, which would defeat the point of an extension.
mausworks
First of all, thanks for a really nice library! We're currently in the process of replacing our proprietary serializer with FlatBuffers and this library is really helpful.
I'm curious if there is any simple way to convert a scalar type in FlatBuffers to a common C# CLR type. This was something which our previous solution handled quite nicely.
In my scenario I want to be able to automatically parse
DateTimeandDateTimeOffsetfrom along(a unix timestamp in milliseconds).Basically, what I want to do is have a custom converter from
longtoDateTime. So when the parser runs across alongwhich has the target CLR-type ofDateTimeorDateTimeOffset, I want to make a quick conversion from a UNIX timestamp, and when the serializer runs across aDateTime, I simply want to output a UNIX timestamp.I've tried to implement an
ITypeModelcalledDateTimeTypeModelbut that interface is really cumbersome to work with. TheRuntimeTypeModelhas an internal constructor, so you can't inherit it, but it would help easing implementation.Any advice on how to do this?