Improve error message for dictionary key converters not implementing ReadAsPropertyName/WriteAsPropertyName. #93406
Description
Description
When I serialize an object that contains a property of type Dictionary<TKey, TValue> and TKey is a custom class, I get a NotSupportedException, even if there is a JSON converter for this.
JsonSerializer.Serialize(
new Custom
{
Dict = new Dictionary<CustomKey, string>
{
[new CustomKey {Value1 = "one", Value2 = "two"}] = "three",
[new CustomKey {Value1 = "four", Value2 = "five"}] = "six"
}});class Custom
{
public Dictionary<CustomKey, string> Dict { get; set; }
}
[JsonConverter(typeof(CustomKeyJsonConverter))]
class CustomKey
{
public string Value1 { get; set; }
public string Value2 { get; set; }
public static CustomKey Parse(string text)
{
var values = text.Split("-");
return new CustomKey {Value1 = values[0], Value2 = values[1]};
}
public override string ToString()
{
return $"{this.Value1}-{this.Value2}";
}
}
class CustomKeyJsonConverter : JsonConverter<CustomKey>
{
public override CustomKey? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
return CustomKey.Parse(reader.GetString());
}
public override void Write(Utf8JsonWriter writer, CustomKey value, JsonSerializerOptions options)
{
writer.WriteStringValue(value.ToString());
}
}Reproduction Steps
see above
Expected behavior
The serialization (and deserialization) should succeed if there is a JSON converter for the key.
Actual behavior
The following NotSupportedException exception is thrown
System.NotSupportedException
The type 'JsonTest.CustomKey' is not a supported dictionary key using converter of type 'JsonTtest.CustomKeyJsonConverter'. The unsupported member type is located on type 'System.String'. Path: $.Dict.
at System.Text.Json.ThrowHelper.ThrowNotSupportedException(WriteStack& state, NotSupportedException ex)
at System.Text.Json.Serialization.JsonConverter`1.WriteCore(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)
at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.Serialize(Utf8JsonWriter writer, T& rootValue, Object rootValueBoxed)
at System.Text.Json.JsonSerializer.WriteString[TValue](TValue& value, JsonTypeInfo`1 jsonTypeInfo)
at System.Text.Json.JsonSerializer.Serialize[TValue](TValue value, JsonSerializerOptions options)
Regression?
The same behavior is in .NET 6, 7 and 8, so it probably not a regression.
Known Workarounds
Write a custom JSON for the whole Dictionary<CustomKey, string> type.
Configuration
Windows 11, ,NET SDK 8.0.100-rc.2.23502.2
Other information
No response