AWS SQS Lambda with .Net SDK - DynamoDBContext dependency injection throws NullReferenceException

Question

I have a simple function generated by AWS Toolkit for Visual Studio, and I'm trying to set up DynamoDBContext with dependency injection. However whenever I try to fetch the IDynamoDBContext from the IServiceProvider, I'm getting a NullReferenceException with no useful information.

Can anyone help me understand what I'm missing?

public interface IMyDependency { }

public class MyDependency : IMyDependency { }

public class Function
{
    public Function()
    {
        var services = ConfigureServices();

        // OK
        var dependency = services.GetService<IMyDependency>();

        // NullReferenceException
        var db = services.GetService<IDynamoDBContext>();
    }

    private IServiceProvider ConfigureServices()
    {
        var services = new ServiceCollection();

        services.AddTransient<IMyDependency, MyDependency>();
        
        services.AddAWSService<IAmazonDynamoDB>();
        services.AddTransient<IDynamoDBContext, DynamoDBContext>();

        return services.BuildServiceProvider();
    }
}

My project file:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <GenerateRuntimeConfigurationFiles>true</GenerateRuntimeConfigurationFiles>
    <AWSProjectType>Lambda</AWSProjectType>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Amazon.Lambda.Core" Version="1.2.0" />
    <PackageReference Include="Amazon.Lambda.Serialization.SystemTextJson" Version="2.1.0" />
    <PackageReference Include="Amazon.Lambda.SQSEvents" Version="1.2.0" />
    <PackageReference Include="AWSSDK.DynamoDBv2" Version="3.5.3.2" />
    <PackageReference Include="AWSSDK.Extensions.NETCore.Setup" Version="3.3.101" />
    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="5.0.0" />
  </ItemGroup>
</Project>

Edit:

Stack trace from the exception that's thrown:

at Amazon.Extensions.NETCore.Setup.ClientFactory.CreateConfig(Type serviceInterfaceType, AWSOptions options) in D:\\JenkinsWorkspaces\\trebuchet-stage-release\\AWSDotNetPublic\\extensions\\src\\AWSSDK.Extensions.NETCore.Setup\\ClientFactory.cs:line 171
at Amazon.Extensions.NETCore.Setup.ClientFactory.CreateServiceClient(ILogger logger, Type serviceInterfaceType, AWSOptions options) in D:\\JenkinsWorkspaces\\trebuchet-stage-release\\AWSDotNetPublic\\extensions\\src\\AWSSDK.Extensions.NETCore.Setup\\ClientFactory.cs:line 89
at Amazon.Extensions.NETCore.Setup.ClientFactory.CreateServiceClient(IServiceProvider provider) in D:\\JenkinsWorkspaces\\trebuchet-stage-release\\AWSDotNetPublic\\extensions\\src\\AWSSDK.Extensions.NETCore.Setup\\ClientFactory.cs:line 75
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRootCache(ServiceCallSite singletonCallSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitDisposeCache(ServiceCallSite transientCallSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.<RealizeService>b__0(ServiceProviderEngineScope scope)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
at AWSLambda.Example.Function..ctor() in C:\\Source\\Git\\AWSLambda.Example\\AWSLambda.Example\\Function.cs:line 36

You say "no useful information", we say "post the stack trace". — Ian Kemp - SO dead by AI greed
– Ian Kemp - SO dead by AI greed, Commented Nov 19, 2020 at 12:40
@IanKemp Good call, I've included that in the description. Thanks — devklick
– devklick, Commented Nov 19, 2020 at 12:47

devklick · Accepted Answer · 2020-11-23 13:26:52Z

The problem was that I had to add the default AWS options.

I added the JSON configuration in appsettings:

  "AWS": {
    "Region": "eu-west-2"
  }

Build the configuration within the function constructor:

public Function()
{
   var config = ConfigureAppConfiguration();
   var services = ConfigureServices(config);

   // ...
}

private IConfiguration ConfigureAppConfiguration()
{
    return new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
        .AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT")}.json", optional: true)
        .AddEnvironmentVariables()
        .Build();
}

And updated the ConfigureServices method to add the AWS options:

private IServiceProvider ConfigureServices(IConfiguration config)
{
    var services = new ServiceCollection();

    services.AddTransient<IMyDependency, MyDependency>();

    services.AddDefaultAWSOptions(config.GetAWSOptions()); // <-- This was mssing
    services.AddAWSService<IAmazonDynamoDB>();
    services.AddTransient<IDynamoDBContext, DynamoDBContext>();

    return services.BuildServiceProvider();
}

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