How in azure function bind event hub output parameter via attributes

Question

I want to bind input and output parameters from and to event hub using attributes.

In a documentation there is only information how to bind to output using return statement https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-event-hubs#output---c-example

[FunctionName("EventHubOutput")] [return: EventHub("outputEventHubMessage", Connection = "EventHubConnectionAppSetting")] public static string Run([TimerTrigger("0 */5 * * * *")] TimerInfo myTimer, TraceWriter log) { log.Info($"C# Timer trigger function executed at: {DateTime.Now}"); return $"{DateTime.Now}"; }

But I want to use ICollector<EventData> outputEventHub as a parameter to have something as below

[FunctionName("EventHubRewriter")]
public static void Run([EventHubTrigger("samples-workitems", Connection ="EventHubInputConnectionAppSetting")] EventData[] inputMessages, ICollector<EventData> outputMessages, TraceWriter log)
{
    ...
}

How to generate binding using attributes for the output event hub?

Update: Here is an info how function.json is gnerated for attribute binding: function.json generation

Mikhail Shilkov · Accepted Answer · 2018-04-16 21:20:20Z

3

It's almost exactly the same:

[EventHub("outputEventHubMessage", Connection = "EventHubConnectionAppSetting")] 
ICollector<EventData> outputMessages

The full signature:

[FunctionName("EventHubRewriter")]
public static void Run(
    [EventHubTrigger("samples-workitems", Connection ="EventHubInputConnectionAppSetting")] 
    EventData[] inputMessages, 
    [EventHub("outputEventHubMessage", Connection = "EventHubConnectionAppSetting")]
    ICollector<EventData> outputMessages, 
    TraceWriter log)
{
    ...
}

answered Apr 16, 2018 at 21:20

Mikhail Shilkov

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8 Comments

wolszakp Over a year ago

I thought it is like that. But after deploy it generates me function.json as below: ` { "generatedBy": "Microsoft.NET.Sdk.Functions.Generator-1.0.6", "configurationSource": "attributes", "bindings": [ { "type": "eventHubTrigger", "connection": "EventHubInputConnectionAppSetting", "path": "output", "name": "eventDataSet" } ], "disabled": false, "scriptFile": "../bin/EventHub.dll", "entryPoint": "EventHub.Ordered.Run" } `

Mikhail Shilkov Over a year ago

@wolszakp That's ok. Input/Output bindings are not included into auto-generated function.json

wolszakp Over a year ago

Ok thanks for an explanation. But what's a reason to use this attributes - I thought that thanks to this attributes function.json will be automatically generated.

Mikhail Shilkov Over a year ago

@wolszakp Runtime will use the attribute directly, skipping function.json sectuon

wolszakp Over a year ago

I meant what is in documentation: Ok thanks for an explanation. But what's a reason to use this attributes - I thought that thanks to this attributes function.json will be automatically generated. I am pointing what is in documentation: learn.microsoft.com/en-us/azure/azure-functions/…

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