Serializer customization using `ICosmosDBSerializerFactory` does not work

I created a class that implements ICosmosDBSerializerFactory and tried to customize the default serializer, but it did not work correctly because CreateSerializer was not called.

It seems that after adding the customized ICosmosDBSerializerFactory to the DI, the Cosmos DB Extension overrides it with the default SerializerFactory.

The initialization by Startup seems to be done in the order of Function App => Extensions, so if the Extension provides an extensible interface, it need to use TryAddSingleton. (In Function Extensions, it could be a convention to use TryAddSingleton)

• https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/storage/Microsoft.Azure.WebJobs.Extensions.Storage.Blobs/src/StorageBlobsWebJobsBuilderExtensions.cs
• https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/storage/Microsoft.Azure.WebJobs.Extensions.Storage.Queues/src/StorageQueuesWebJobsBuilderExtensions.cs

Repro steps

public class Startup : FunctionsStartup
{
    public override void Configure(IFunctionsHostBuilder builder)
    {
        builder.Services.AddSingleton<ICosmosDBSerializerFactory, MyCosmosDBSerializerFactory>();
    }
}

public class MyCosmosDBSerializerFactory : ICosmosDBSerializerFactory
{
    public CosmosSerializer CreateSerializer()
    {
        var options = new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase
        };

        // From https://github.com/Azure/azure-cosmos-dotnet-v3/blob/master/Microsoft.Azure.Cosmos.Samples/Usage/SystemTextJson/CosmosSystemTextJsonSerializer.cs
        return new CosmosSystemTextJsonSerializer(options);
    }
}

Expected behavior

The customized SerializerFactory will be used.

Actual behavior

The default implementation of SerializerFactory is always used.

Known workarounds

Not available.

Related information

• Microsoft.Azure.WebJobs.Extensions.CosmosDB : 4.0.0-preview1
• https://github.com/Azure/azure-webjobs-sdk-extensions/blob/dev/src/WebJobs.Extensions.CosmosDB/Config/CosmosDBWebJobsBuilderExtensions.cs#L36

[ealsur]

Should be fixed in preview2 release

[ealsur]

Yeah, I added a test with the inverted order (injection first then AddCosmosDB) and that initially failed (that’s how I came to the conclusion about the order), with the TryAddSingleton change, then both tests passed. Thanks for the pointer to the other examples, that was very useful.