C#•2y ago

Implementing JsonConverter to simplify ser/de

I've been trying to implemement a JsonConverter for a simple class to simplify the default C# tagging using JsonSerializer. Here's the class I'm trying to convert:

public class Snapshot<T>
{
    public DateTime Taken { get; set; }
    public T Data { get; set; }

    public static Snapshot<T> NewEmpty()
    {
        return new Snapshot<T>
        {
            Taken = DateTime.MinValue,
            Data = default
        };
    }
}

public class Snapshot<T>
{
    public DateTime Taken { get; set; }
    public T Data { get; set; }

    public static Snapshot<T> NewEmpty()
    {
        return new Snapshot<T>
        {
            Taken = DateTime.MinValue,
            Data = default
        };
    }
}

And here's an example serialized output for what I need:

{"2020-06-21T00:00:00":"this is some data here!!"}

{"2020-06-21T00:00:00":"this is some data here!!"}

(FYI the default serializer outputs {"Taken":"2020-06-21T00:00:00","Data":"this is some data here!!"}). How do I implement a JsonConverter to Read & Write to my desired format? I need the generics to always work and this Snapshot will be used as an attribute of a parent class I've wrote this so far which feels like it's going in the right direction, but I'm not sure if the JsonSerializer line here is right and I'm not sure about how to implement Read:

public class SnapshotConverter<T> : JsonConverter<Snapshot<T>>
{
    public override Snapshot<T> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        throw new NotImplementedException("Deserialization is not supported.");
    }

    public override void Write(Utf8JsonWriter writer, Snapshot<T> value, JsonSerializerOptions options)
    {
        writer.WriteStartObject();
        writer.WritePropertyName(value.Taken.ToString("s"));
        JsonSerializer.Serialize(writer, value.Data, options);
        writer.WriteEndObject();
    }
}

public class SnapshotConverter<T> : JsonConverter<Snapshot<T>>
{
    public override Snapshot<T> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        throw new NotImplementedException("Deserialization is not supported.");
    }

    public override void Write(Utf8JsonWriter writer, Snapshot<T> value, JsonSerializerOptions options)
    {
        writer.WriteStartObject();
        writer.WritePropertyName(value.Taken.ToString("s"));
        JsonSerializer.Serialize(writer, value.Data, options);
        writer.WriteEndObject();
    }
}

30 Replies

ero•2y ago

quite sure this is impossible

OwezOP•2y ago

Are there any libraries to do this sort of thing? I'm basically reimplementing my rust client in C#

ero•2y ago

i mean i'll just be real, this is a really bad json layout like, awful

Vi Ness•2y ago

{"2020-06-21T00:00:00":"this is some data here!!"}

{"2020-06-21T00:00:00":"this is some data here!!"}

Looks like a KeyValuePair entry for a Dictionary<DateTime, T>. Would that be an option instead of using Snapshot<T>?

OwezOP•2y ago

God yeah I messed up Thats the json for the Element Haha hang on let me get the actual class Sorry about that

ero•2y ago

dictionary is the only thing i can think of as well but the key of a json entry must be a string so

OwezOP•2y ago

I think I was debugging the wrong class for a little while, I'll check if it applies and send the right problem :)

ero•2y ago

the date should definitely never be the key

Vi Ness•2y ago

This looks like an answer to a similar issue https://stackoverflow.com/a/41503997

Stack Overflow

Serialize List> as JSON

I'm very new with JSON, please help! I am trying to serialise a List<KeyValuePair<string, string>> as JSON Currently: [{"Key":"MyKey 1","Value":"MyValue 1"},{"Key":"MyKey 2","Value":"

OwezOP•2y ago

Yeah the JSON is for a class with a dictionary inside (called Elements), posted the wrong bit but I was debugging assuming that JSON which is why I couldn't get it to work Had the wrong test case Yep seems to work This is what I actually needed help with haha:

public class Elements<T>
{
    public Dictionary<DateTime, T> Values { get; set; }

    public Elements(Dictionary<DateTime, T> values)
    {
        Values = values;
    }

    public static Elements<T> NewTest(string isoDateString, T firstValue)
    {
        DateTime parsedDate = DateTime.Parse(isoDateString);
        Dictionary<DateTime, T> values = new Dictionary<DateTime, T>
        {
            { parsedDate, firstValue }
        };
        return new Elements<T>(values);
    }
}

public class Elements<T>
{
    public Dictionary<DateTime, T> Values { get; set; }

    public Elements(Dictionary<DateTime, T> values)
    {
        Values = values;
    }

    public static Elements<T> NewTest(string isoDateString, T firstValue)
    {
        DateTime parsedDate = DateTime.Parse(isoDateString);
        Dictionary<DateTime, T> values = new Dictionary<DateTime, T>
        {
            { parsedDate, firstValue }
        };
        return new Elements<T>(values);
    }
}

How do I flatten this so there's no {"Values": [data here]} so its only {[data here]} I need it as a class because it's got related methods otherwise it'd just be a Dictionary. In rust this would look like

#[derive(Serialize, Deserialize)]
pub struct Elements<T>(HashMap<DateTime<Utc>, T>)

#[derive(Serialize, Deserialize)]
pub struct Elements<T>(HashMap<DateTime<Utc>, T>)

ero•2y ago

class Elements<T> : Dictionary<DateTime, T>? but again, the datetime being the key is really weird...

OwezOP•2y ago

Did not think about that Timeseries data

ero•2y ago

don't know what that means

OwezOP•2y ago

title here is Elements<string> for example

OwezOP•2y ago

I'm writing a youtube archiver which can snapshot metadata at different places in time

ero•2y ago

this seems really backwards

ACiDCA7•2y ago

i think with this you just disqualified yourself from getting anymore help, since to me to me it seems like you are scraping data from yt which iirc is against tos

OwezOP•2y ago

the only other way to do it is like that original Snapshot class in a list but then you lose the hashtable

ero•2y ago

{
  snapshots: [
    {
      "date": "...",
      "title": "...",
      // ...
    },
    // more snapshots
  ]
}

{
  snapshots: [
    {
      "date": "...",
      "title": "...",
      // ...
    },
    // more snapshots
  ]
}

this would definitely be better but yeah we can't help with scraping

OwezOP•2y ago

metadata captures not perfect so sometimes only certain things are either updated or remain unchanged

ero•2y ago

sure

OwezOP•2y ago

and Elements means each is generalised

ero•2y ago

what's it matter

OwezOP•2y ago

title.current() a lot easier with ISO alphabetically sorted dates

ero•2y ago

snapshots.orderby(date).first().title

OwezOP•2y ago

rather than having to linear search through each snapshot and then see if theres a title in there or if its not been captured or not been updated im tracking each update not each time ive possibly captured it

ero•2y ago

also btw currently all your dates are messed up

OwezOP•2y ago

yep they should all use the same time

ero•2y ago

cause you fetch datetime.now anew every single time

OwezOP•2y ago

any more critiques? i guess not

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Implementing JsonConverter to simplify ser/de