Azure Functions: CosmosDBTrigger not triggering in Visual Studio

Question

TL;DR: This example is not working for me in VS2017.

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I have an Azure Cosmos DB and want to fire some logic when something adds or updates there. For that, CosmosDBTrigger should be great.

Tutorial demonstrates creating trigger in Azure Portal and it works for me. However, doing just the same thing in Visual Studio (15.5.4, latest by now) does not.

I use the default Azure Functions template, predefined Cosmos DB trigger and nearly default code:

[FunctionName("TestTrigger")]
public static void Run(    
    [CosmosDBTrigger("Database", "Collection", ConnectionStringSetting = "myCosmosDB")]
    IReadOnlyList<Document> input,
    TraceWriter log)
    {
        log.Info("Documents modified " + input.Count);
        log.Info("First document Id " + input[0].Id);
    }

App runs without errors but nothing happens when I actually do stuff in the database. So I cannot debug things and actually implement some required logic.

Connection string is specified in the local.settings.json and is considered. If I deliberately foul it, trigger spits runtime errors.

It all looks like the connection string is to a wrong database. But it is exactly the one, copypasted, string I have in the trigger made via Azure Portal.

Where could I go wrong? What else can I check?

Answer 1

Based on your comment, you were running both portal and local Apps at the same time for the same collection and the same lease collection.

That means both Apps were competing to each other for locks (leases) on collection processing. The portal App won in your case, took the lease, so the local App was sitting doing nothing.