C#

C# (CSharp)

The dotnet8-csharp template is a C# template built with WebApplication and the minimal API style. It is multi-arch, and can be deployed to an amd64 or arm64 platform.

For a function based upon an existing project or Dockerfile, see: Build ASP.NET Core APIs with Kubernetes and OpenFaaS

Create a new function

faas-cli template store pull dotnet8-csharp

export PREFIX=ttl.sh

faas-cli new \
    --lang dotnet8-csharp \
    my-function

Add a dependency

To manage dependencies, edit the Function.csproj file and add an <ItemGroup> with <PackageReference>

<ItemGroup>
    <PackageReference Include="Npgsql" Version="8.0.2" />
</ItemGroup>

Or, run the dotnet command, i.e.

dotnet add my-function package Npgsql --version 8.0.2

Add static files

You may want to copy static files into the final image such as a SQLite database, JSON data, HTML files or text templates for emails.

If a folder named static is found in the root of your function's source code, it will be copied into the final image published for your function.

To serve the contents of the static folder you can setup the file server in Handler.cs.

    public static void MapEndpoints(WebApplication app) {
        app.UseStaticFiles();
    }

Swagger

To add Swagger to an endpoint, edit Handler.cs and add the following:

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;

namespace function;

public static class Handler
{
    public static void MapServices(IServiceCollection services)
    {
        services.AddEndpointsApiExplorer();
        services.AddSwaggerGen();

        // register additional services
    }

    public static void Map(WebApplication app)
    {
        app.UseSwagger();
        app.UseSwaggerUI();

        app.MapGet("/customers", () =>
        {
            return "A list of customers";
        })
        .WithOpenApi();
    }
}

Add the required package references to the Function.csproj file:

dotnet CLIxml

dotnet add my-function \
    package Microsoft.AspNetCore.OpenApi --version 8.0.3
dotnet add my-function \
    package Swashbuckle.AspNetCore --version 6.4.0

<ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="8.0.3" />
    <PackageReference Include="Swashbuckle.AspNetCore" Version="6.4.0" />
</ItemGroup>

You can then view the swagger UI by visiting http://127.0.0.1:8080/function/my-function/swagger, or the swagger JSON by clicking on the link displayed.

Query a PostgreSQL database

Add a NuGet reference to the Npgsql package to the Function.csproj file.

Either edit the Function.csproj file directly or use the dotnet cli.

dotnet CLIxml

dotnet add my-function package Npgsql --version 8.0.2

<ItemGroup>
    <PackageReference Include="Npgsql" Version="8.0.2" />
</ItemGroup>

Edit Handler.cs to query the postgreSQL database:

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Npgsql;

namespace function;

public static class Handler
{
    // MapEndpoints is used to register WebApplication
    // HTTP handlers for various paths and HTTP methods.
    public static void MapEndpoints(WebApplication app)
    {
        var connectionString = File.ReadAllText("/var/openfaas/secrets/pg-connection");
        var dataSource = NpgsqlDataSource.Create(connectionString);

        app.MapGet("/customers", async () =>
        {   
            var customers = new List<Customer>();
            await using (var cmd = dataSource.CreateCommand("SELECT id, name, email FROM customer"))
            await using (var reader = await cmd.ExecuteReaderAsync())
            {
                while (await reader.ReadAsync())
                {
                    customers.Add(new Employee{
                        Id = (int)reader["id"],
                        Name = reader.GetString(1),
                        Email = reader.GetString(2)
                    });
                }
            }
            return Results.Ok(customers);
        });
    }

    // MapServices can be used to configure additional
    // WebApplication services
    public static void MapServices(IServiceCollection services)
    {
    }
}

public class Customer {
    public int Id { get; set; }
    public string? Name { get; set; }
    public string? Email { get; set; }
}

The functions reads the PostgreSQL connection string from an OpenFaaS secret. Make sure the secret is created and referenced in the stack.yml file before deploying the function.

The connection string for Postgres should be formatted like this:

Host=postgresql;Username=postgres;Password=mysecretpassword;Database=postgres