Skip to main content

C#–Declaring attributes on positional record types

In C# 9 record types were introduced.

A record in C# is a class or struct that provides special syntax and behavior for working with data models.

What makes them different from a ‘normal’ class or struct is that they offer the following functionality:

  • Value equality: Two record types are equal if the types match and all property and fields match
  • Immutability: You cannot change any property or field value after instantiation

You have 2 ways to define a record type. One way is similar to what you already know when creating classes or structs:

A second way is through positional parameters:

Behind the scenes, the compiler does a lot of work for us as it creates:

  • A public autoimplemented property for each positional parameter provided in the record declaration
  • A primary constructor whose parameters match the positional parameters on the record declaration.  
  • A Deconstruct method with an out parameter for each positional parameter provided in the record declaration. The method deconstructs properties defined by using positional syntax; it ignores properties that are defined by using standard property syntax.

This makes our live a lot easier. No reason to complain.

But what if we want to add metadata to the generated properties?

Good question! The good news is that we can declare attributes at the positional parameter level and specify a target:


In the example above the System.Text.Json.Serialization.JsonPropertyNameAttribute is assigned to each property of the Person record. The property target is used to specify that the attribute applies to the compiler-generated property.

More information

Records in C# - C# | Microsoft Learn

Records - C# reference - C# | Microsoft Learn

Popular posts from this blog

DevToys–A swiss army knife for developers

As a developer there are a lot of small tasks you need to do as part of your coding, debugging and testing activities.  DevToys is an offline windows app that tries to help you with these tasks. Instead of using different websites you get a fully offline experience offering help for a large list of tasks. Many tools are available. Here is the current list: Converters JSON <> YAML Timestamp Number Base Cron Parser Encoders / Decoders HTML URL Base64 Text & Image GZip JWT Decoder Formatters JSON SQL XML Generators Hash (MD5, SHA1, SHA256, SHA512) UUID 1 and 4 Lorem Ipsum Checksum Text Escape / Unescape Inspector & Case Converter Regex Tester Text Comparer XML Validator Markdown Preview Graphic Color B

Help! I accidently enabled HSTS–on localhost

I ran into an issue after accidently enabling HSTS for a website on localhost. This was not an issue for the original website that was running in IIS and had a certificate configured. But when I tried to run an Angular app a little bit later on http://localhost:4200 the browser redirected me immediately to https://localhost . Whoops! That was not what I wanted in this case. To fix it, you need to go the network settings of your browser, there are available at: chrome://net-internals/#hsts edge://net-internals/#hsts brave://net-internals/#hsts Enter ‘localhost’ in the domain textbox under the Delete domain security policies section and hit Delete . That should do the trick…

Azure DevOps/ GitHub emoji

I’m really bad at remembering emoji’s. So here is cheat sheet with all emoji’s that can be used in tools that support the github emoji markdown markup: All credits go to rcaviers who created this list.