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warning SYSLIB1037: The type '' defines init-only properties, deserialization of which is currently not supported in source generation mode.

2 days ago I introduced the System.Text.Json source generator and showed you how to use it in ASP.NET Core. What I didn’t told you that it didn’t go so smoothly.

If you had a good look at the generated code I shared, you maybe noticed the following lines:

The generated setter on the property will not work and instead throw an InvalidOperationException.

This also appears as a warning during the build process:

CSC : warning SYSLIB1037: The type 'OrderDto' defines init-only properties, deserialization of which is currently not supported in source generation mode.

More information about this warning: https://docs.microsoft.com/en-us/dotnet/fundamentals/syslib-diagnostics/syslib1037

The reason is that my OrderDto is a record type using init-only properties:

There is not much we can do to fix this else then switching to mutable properties:

I searched around further on the web about this issue and found the following related Github issues:

The good news that Microsoft is looking into this issue and that maybe a solution will be provided in .NET 7.

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