StronglyTypedId requires requires the .NET Core SDK v6.0.100 or greater.

Changes in version 1.x

Version 0.x of this library used the helper library CodeGeneration.Roslyn by AArnott, for build-time source generation. In version 1.0.0 this approach has been completely replaced in favour of source generators, as these are explicitly supported in .NET 6+. As part of this change, there were a number of additional features added and breaking changes made.

Breaking Changes

• StronglyTypedIds namespace is required. In version 0.x of the library, the [StronglyTypedId] attribute was in the global namespace. In version 1.x, the attribute is in the StronglyTypedIds namespace, so you must add namespace StronglyTypedIds;.
• The properties exposed by StronglyTypedIds have changed: there is no longer a generateJsonConverter property. Instead, this is infered based on the StronglyTypedIdConverters flags provided.
• The String backing typed ID will throw if you call the constructor with a null value

New Features

• The attributes can now auto-generate additional converter types such as EF Core ValueConverter and Dapper TypeHandler, as described in my blog posts. These are optional flags on the converters property.
• Made interface implementations (IEquatable<T> and IComparable<T> currently) optional. This is to potentially support additional interfaces in future versions.
• Added a NullableString backing type. Due to the behaviour of structs in c#, the String backing type ID may still be null, but you can't explicitly call the constructor with a null value. In contrast, you can do this with the NullableString backing type.
• Added a [StronglyTypedIdDefaults] attribute to set default values for all [StronglyTypedId] attributes in your project. This is useful if you want to customise all the attributes, for example, if you want to generate additional converters by default. You can still override all the properties of a [StronglyTypedId] instance.

Bug Fixes

• Some converters had incorrect implementations, such as in (#24). These have been addressed in version 1.x.
• Better null handling has been added for the String backing type, handling issues such as #32.
• The code is marked as auto generated, to avoid errors such as #CS1591 as described in #27
• An error deserializing nullable StronglyTypedIds with Newtonsoft.Json #36

Installing

To use the the StronglyTypedId NuGet package, install the StronglyTypedId package into your project. Depending on which converters you implement, you may need one or more of the following additional packages

• Newtonsoft.Json (optional, only required if generating a Newtonsoft JsonConverter). Note that in some ASP.NET Core apps, you will likely already reference this project via transitive dependencies.
• System.Text.Json (optional, only required if generating a System.Text JsonConverter). Note that in .NET Core apps, you will likely already reference this project via transitive dependencies.
• Dapper (optional, only required if generating a type mapper)
• EF Core (optional, only required if generating an EF Core ValueConverter)

To install the packages, add the references to your csproj file so that it looks something like the following:

Usage

To create a strongly-typed ID, create a partial struct with the desired name, and decorate it with the [StronglyTypedId] attribute, in the StronglyTypedIds namespace:

This generates the "default" strongly-typed ID using a Guid backing field, a custom TypeConverter, and a custom JsonConverter based on Newtonsoft.Json.

Customising the converters

You can customise which converters to generate by using flags. For example, to generate a TypeConverter, a System.Text.JsonConverter, and an EF Core ValueConverter, use

Using different types as a backing fields

The default strongly-typed ID uses a Guid backing field:

You can choose a different type backing field, by passing a value of the StronglyTypedIdBackingType enum in the constructor.

Currently supported values are Guid (the default), int, long, and string.

Error CS0436 and [InternalsVisibleTo]

The StronglyTypedId generator automatically adds the [StronglyTypedId] attributes to your compilation as internal attributes. If you add the source generator package to multiple projects, and use the [InternalsVisibleTo] attribute, you may experience errors when you build:

Removing the [InternalsVisibleTo] attribute will resolve the problem, but if this is not possible you can disable the auto-generation of the [StronglyTypedId] marker attributes, and rely on the helper StronglyTypedId.Attributes package instead. This package contains the same attributes, but as they are in an external package, you can avoid the CS0436 error.

Add the package to your solution, ensuring you set "PrivateAssets="All" in the <PackageReference> (this will be done automatically when using the .NET CLI or an IDE). To disable the auto-generation of the marker attributes, define the constant STRONGLY_TYPED_ID_EXCLUDE_ATTRIBUTES in your project file. Your project file should look something like the following:

The attribute library is only required at compile time, so it won't appear in your build output.

Why do I need this library?

I have written a blog-post series on strongly-typed IDs that explains the issues and rational behind this library. For a detailed view, I suggest starting there, but I provide a brief introduction here.

This library is designed to tackle a specific instance of primitive obsession, whereby we use primitive objects (Guid/string/int/long etc) to represent the IDs of domain objects. The problem is that these IDs are all interchangeable - an order ID can be assigned to a product ID, despite the fact that is likely nonsensical from the domain point of view. See here for a more concrete example.

By using strongly-typed IDs, we give each ID its own Type which wraps the underlying primitive value. This ensures you can only use the ID where it makes sense: ProductIds can only be assigned to products, or you can only search for products using a ProductId, not an OrderId.

Unfortunately, taking this approach requires a lot of boilerplate and ceremony to make working with the IDs manageable. This library abstracts all that away from you, by generating the boilerplate at build-time by using a Roslyn-powered code generator.

What code is generated?

The exact code generated depends on the arguments you provide to the StronglyTypedId attribute. The code is generated to the obj folder of the project, so you can use Go to Definition on your Id to see the exact code generated in each case.

You can see see example implementations in the test SourceGenerationHelperSnapshotTests in which all permutations of the attribute are tested, and examples generated in the snapshots folder.

Requirements

The StronglyTypedId NuGet package is a .NET Standard 2.0 package.

You must be using the .NET 6+ SDK (though you can compile for other target frameworks like .NET Core 2.1 and .NET Framework 4.8)

The structs you decorate with the StronglyTypedId attribute must be marked partial.

Credits

StronglyTypedId wouldn't work if not for AArnott's CodeGeneration.Roslyn library.

The build process and general design of the library was modelled on the RecordGenerator project, which is similar to this project, but can be used to generate immutable Record types.