System.Text.Json: The collection type ‘System.Collections.Generic.Dictionary[System.Int32,System.String]is not supported

Issue Description

JSON serialization using System.Text.Json produces the below error in the.NET/.NET Core application.

System.NotSupportedException: 'The collection type 'System.Collections.Generic.Dictionary`2[System.Int32,System.String]' is not supported.'

SystemTextJson The collection type Dictionary with integer Key not supported

Resolution

This issue is more because the new .NET /ASP.NET Core 3.1 or .NET 5.0 framework has removed the dependency on JSON.NET(Newtonsoft) and uses its own JSON serializer i.e. ‘System.Text.Json‘.

System.Text.Json has built-in support for only Dictionary types that match Dictionary< string, TValue>.

It produces NotSupportedException for the non-string Keys like Int32 or Enum in the serialization.

As per specification and design, there are known limitations in the System.Text.Json serializer for the serialization.

Resolution 1 (Recommended):

These limitations can be overcome by using Custom DictionaryConverter.

I have the dictionary object below,

Dictionary<int, string> dictEmployess = new Dictionary<int, string>();

The issue can be fixed by using DictionaryInt32Converter as a converter in the serialization option.

            var serializeOptions = new JsonSerializerOptions();
            serializeOptions.Converters.Add(new DictionaryInt32Converter());
            jsonoutPut = JsonSerializer.Serialize(dictEmployess);

Please see here an example of DictionaryInt32Converter.

Resolution 2:

Continue using Newtonsoft(JSON.NET) as is. This option is very easy however you end up using a big fat Newtonsoft library.

jsonoutPut = JsonConvert.SerializeObject(dictEmployess);

Did I miss anything else in these resolution steps?

Did the above steps resolve your issue? Please sound off your comments below!

Happy Coding !!

Reference :



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