Adding a Dictionary<DateTime,T> to a mongoDb when using C# monogDb drivers

Question

Currently I am trying to add an object that has a property Dictionary<DateTime,T> to a mongoDb by using the c# monogDb driver.

In the project I have a lot of related legacy code so I can't easily change the dictionary to any other type. Dictionaries are a quiter common data type in my project so adding a seperate tag above all properties to define the serializer isn't really a good options. I would like to find a general way serializing the dictionary.

I have read the following related post, and tried applying the convetion, however this seems to give me issues with the child serializer.

When adding an item I get the following error:

System.InvalidOperationException: ValueFactory attempted to acces the value property of this instace.

I can't figure out what the issue exactly is or how to solve it.

Answer 1

As recommended by @Poul Bak the issue can be solved as the following:

As an example I will use a class Item

public class Item {
     public Dictionary<DateTime, AnotherItem> Dictionary {get;set;}
}

Create a value converter

    public class DateTimeDictionaryConverter<T>: ValueConverter<Dictionary<DateTime, T>, string> {

    public DateTimeDictionaryConverter() : base(
        v => ConvertToJson(v),
        v => ConvertFromJson(v))
    {
    }

    private static string ConvertToJson(Dictionary<DateTime, T> dict)
    {
        return JsonSerializer.Serialize(dict);
    }

    private static Dictionary<DateTime, T> ConvertFromJson(string value)
    {
        return JsonSerializer.Deserialize<Dictionary<DateTime, T>>(value);
    }
}

Then add the converter to the correct entity in the db context

modelBuilder.Entity<Item>().Property(i => i.Dictionary).HasConversion(new DateTimeDictionaryConverter<OtherItem>())

This wil work, the only remaining downside is having to add the value converter for each item with a dictionary