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Strongly

Strongly logo

Build status NuGet

Strongly makes creating strongly-typed values as easy as adding an attribute! No more accidentally passing arguments in the wrong order to methods - Strongly uses .NET 6's compile-time incremental source generators to generate the boilerplate required to use strongly-typed IDs.

Simply, install the required package add the [Strongly] attribute to a struct (in the Strongly namespace):

using Strongly;
 
[Strongly] // <- Add this attribute to auto-generate the rest of the type
public partial struct FooId { }

and the source generator magically generates the backing code when you save the file! Use Go to Definition to see the generated code:

Generating a strongly-typed ID using the Strongly packages

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

Installing

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

To install the packages, add the references to your csproj file, for example by running

dotnet add package Strongly

This adds a <PackageReference> to your project. You can additionally mark the package as PrivateAssets="all" and ExcludeAssets="runtime".

Setting PrivateAssets="all" means any projects referencing this one will not also get a reference to the Strongly package. Setting ExcludeAssets="runtime" ensures the Strongly.Attributes.dll file is not copied to your build output (it is not required at runtime).

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <OutputType>Exe</OutputType>
        <TargetFramework>net6.0</TargetFramework>
    </PropertyGroup>

    <!-- Add the package -->
    <PackageReference Include="Strongly" Version="1.0.0" PrivateAssets="all" ExcludeAssets="runtime"/>
    <!-- -->

</Project>

Usage

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

using Strongly;

[Strongly] // Add this attribute to auto-generate the rest of the type
public partial struct FooId { }

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

Customising the converters

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

using Strongly;

[Strongly(converters: StronglyConverter.TypeConverter | StronglyConverter.SystemTextJson | StronglyConverter.EfValueConverter)] 
public partial struct SystemTextJsonConverterId { }

Using different types as a backing fields

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

using Strongly;

[Strongly]
public partial struct FooId { }

var id = new FooId(Guid.NewGuid());

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

using Strongly;

[Strongly(backingType: StronglyBackingType.String)]
public partial struct FooId { }

var id = new FooId("my-id-value");

Currently supported values are Guid (the default), int, long,decimal,BigInteger, MassTransit.NewId and string.

Changing the defaults globally

If you wish to change the converters, backing types, or implementations used by default for all the [Strongly] -decorated types in your project, you can use the assembly attribute [StronglyDefaults] to set all of these. For example, the following sets the default converter to a whole project to [SystemTextJson], and changes the default backing-type to an int

// Set the defaults for the project
[assembly:StronglyDefaults(
    backingType: StronglyType.Int,
    converters: StronglyConverter.SystemTextJson)]

[Strongly]
public partial struct OrderId { }

[Strongly]
public partial struct UserId { }

This is equivalent to setting these values manually on all the IDs:

[Strongly(
    backingType: StronglyType.Int,
    converters: StronglyConverter.SystemTextJson)]
public partial struct OrderId { }

[Strongly(
     backingType: StronglyType.Int,
    converters: StronglyConverter.SystemTextJson)]
public partial struct UserId { }

EF Core - ValueConverter

When you create a Strongly type with EF Converter, the type will have a nested ValueConverter class you can use on your entity model definition

[Strongly(StronglyType.String, StronglyConverter.EfValueConverter)]
public partial struct PhoneNumber
{
}

public class MyDbContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder builder)
    {
        var customer = builder.Entity<Customer>();
        customer.Property(x => x.Phone).HasConversion<PhoneNumber.EfValueConverter>();
    }
}

If you have lots of strongly type values you can use the package bellow to automatically set the Strongly ValueConverter on all your entities NuGet

dotnet add package Strongly.EFCore

After installation you need to set it on yor DbContextOptionsBuilder

services
    .AddDbContext<AppDbContext>(options => options
        .UseStronglyTypeConverters()
        /* ... */
        )

OpenApi/Swagger Specification

If you wish to use an ID in your Swagger models and want to have schema and model sample reflecting the value backing-field type you will need:

  • Install Swagger Annotations >=5.0.0
  • Enable annotation in swagger gen with services.AddSwaggerGen(c => c.EnableAnnotations());
  • Use the converter flag StronglyConverter.SwaggerSchemaFilter on the ID decorator. eg: 
    [Strongly(
    backingType: StronglyType.Int,
    converters: StronglyConverter.SwaggerSchemaFilter | StronglyConverter.SystemTextJson)]
public partial struct UserId { }

Embedding the attributes in your project

By default, the [Strongly] attributes referenced in your application are contained in an external dll. It is also possible to embed the attributes directly in your project, so they appear in the dll when your project is built. If you wish to do this, you must do two things:

  1. Define the MSBuild constant STRONGLY_TYPED_EMBED_ATTRIBUTES. This ensures the attributes are embedded in your project
  2. Add compile to the list of excluded assets in your <PackageReference> element. This ensures the attributes in your project are referenced, instead of the Strongly.Attributes.dll library.

Your project file should look something like this:

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <OutputType>Exe</OutputType>
        <TargetFramework>net6.0</TargetFramework>
        <!--  Define the MSBuild constant    -->
        <DefineConstants>STRONGLY_TYPED_EMBED_ATTRIBUTES</DefineConstants>
    </PropertyGroup>

    <!-- Add the package -->
    <PackageReference Include="Strongly" Version="1.0.0"
                      PrivateAssets="all"
                      ExcludeAssets="compile;runtime"/>
    <!--                               ☝ Add compile to the list of excluded assets. -->

</Project>

Preserving usages of the [Strongly] attribute

The [Strongly] and [StronglyDefaults] attributes are decorated with the [Conditional] attribute, so their usage will not appear in the build output of your project. If you use reflection at runtime on one of your IDs, you will not find [Strongly] in the list of custom attributes.

If you wish to preserve these attributes in the build output, you can define the STRONGLY_TYPED_USAGES MSBuild variable. Note that this means your project will have a runtime-dependency on Strongly.Attributes.dll so you need to ensure this is included in your build output.

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <OutputType>Exe</OutputType>
        <TargetFramework>net6.0</TargetFramework>
        <!--  Define the MSBuild constant to preserve usages   -->
        <DefineConstants>STRONGLY_TYPED_USAGES</DefineConstants>
    </PropertyGroup>

    <!-- Add the package -->
    <PackageReference Include="Strongly" Version="1.0.0" PrivateAssets="all"/>
    <!--              ☝ You must not exclude the runtime assets in this case -->

</Project>

Why do I need this library?

Andrew 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/decimal etc) to represent the IDs or values of domain objects. The problem is that these types 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 values, we give each of then its own Type which wraps the underlying primitive value. This ensures you can only use the value 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 it 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 Strongly 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.

Requirements

The Strongly 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 Strongly attribute must be marked partial.

Credits

This project born as a fork of StronglyTypedId