author	ms.service	ms.topic	ms.date	ms.author
craigshoemaker	azure-functions	include	02/21/2020	cshoe

Use the Event Hubs output binding to write events to an event stream. You must have send permission to an event hub to write events to it.

Make sure the required package references are in place before you try to implement an output binding.

C#

The following example shows a C# function that writes a message to an event hub, using the method return value as the output:

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

The following example shows how to use the IAsyncCollector interface to send a batch of messages. This scenario is common when you are processing messages coming from one Event Hub and sending the result to another Event Hub.

[FunctionName("EH2EH")]
public static async Task Run(
    [EventHubTrigger("source", Connection = "EventHubConnectionAppSetting")] EventData[] events,
    [EventHub("dest", Connection = "EventHubConnectionAppSetting")]IAsyncCollector<string> outputEvents,
    ILogger log)
{
    foreach (EventData eventData in events)
    {
        // do some processing:
        var myProcessedEvent = DoSomething(eventData);

        // then send the message
        await outputEvents.AddAsync(JsonConvert.SerializeObject(myProcessedEvent));
    }
}

C# Script

The following example shows an event hub trigger binding in a function.json file and a C# script function that uses the binding. The function writes a message to an event hub.

The following examples show Event Hubs binding data in the function.json file. The first example is for Functions 2.x and higher, and the second one is for Functions 1.x.

{
    "type": "eventHub",
    "name": "outputEventHubMessage",
    "eventHubName": "myeventhub",
    "connection": "MyEventHubSendAppSetting",
    "direction": "out"
}

{
    "type": "eventHub",
    "name": "outputEventHubMessage",
    "path": "myeventhub",
    "connection": "MyEventHubSendAppSetting",
    "direction": "out"
}

Here's C# script code that creates one message:

using System;
using Microsoft.Extensions.Logging;

public static void Run(TimerInfo myTimer, out string outputEventHubMessage, ILogger log)
{
    String msg = $"TimerTriggerCSharp1 executed at: {DateTime.Now}";
    log.LogInformation(msg);   
    outputEventHubMessage = msg;
}

Here's C# script code that creates multiple messages:

public static void Run(TimerInfo myTimer, ICollector<string> outputEventHubMessage, ILogger log)
{
    string message = $"Message created at: {DateTime.Now}";
    log.LogInformation(message);
    outputEventHubMessage.Add("1 " + message);
    outputEventHubMessage.Add("2 " + message);
}

JavaScript

The following example shows an event hub trigger binding in a function.json file and a JavaScript function that uses the binding. The function writes a message to an event hub.

The following examples show Event Hubs binding data in the function.json file. The first example is for Functions 2.x and higher, and the second one is for Functions 1.x.

{
    "type": "eventHub",
    "name": "outputEventHubMessage",
    "eventHubName": "myeventhub",
    "connection": "MyEventHubSendAppSetting",
    "direction": "out"
}

{
    "type": "eventHub",
    "name": "outputEventHubMessage",
    "path": "myeventhub",
    "connection": "MyEventHubSendAppSetting",
    "direction": "out"
}

Here's JavaScript code that sends a single message:

module.exports = function (context, myTimer) {
    var timeStamp = new Date().toISOString();
    context.log('Message created at: ', timeStamp);   
    context.bindings.outputEventHubMessage = "Message created at: " + timeStamp;
    context.done();
};

Here's JavaScript code that sends multiple messages:

module.exports = function(context) {
    var timeStamp = new Date().toISOString();
    var message = 'Message created at: ' + timeStamp;

    context.bindings.outputEventHubMessage = [];

    context.bindings.outputEventHubMessage.push("1 " + message);
    context.bindings.outputEventHubMessage.push("2 " + message);
    context.done();
};

Python

The following example shows an event hub trigger binding in a function.json file and a Python function that uses the binding. The function writes a message to an event hub.

The following examples show Event Hubs binding data in the function.json file.

{
    "type": "eventHub",
    "name": "$return",
    "eventHubName": "myeventhub",
    "connection": "MyEventHubSendAppSetting",
    "direction": "out"
}

Here's Python code that sends a single message:

import datetime
import logging
import azure.functions as func


def main(timer: func.TimerRequest) -> str:
    timestamp = datetime.datetime.utcnow()
    logging.info('Message created at: %s', timestamp)
    return 'Message created at: {}'.format(timestamp)

Java

The following example shows a Java function that writes a message containing the current time to an Event Hub.

@FunctionName("sendTime")
@EventHubOutput(name = "event", eventHubName = "samples-workitems", connection = "AzureEventHubConnection")
public String sendTime(
   @TimerTrigger(name = "sendTimeTrigger", schedule = "0 */5 * * * *") String timerInfo)  {
     return LocalDateTime.now().toString();
 }

In the Java functions runtime library, use the @EventHubOutput annotation on parameters whose value would be published to Event Hub. The parameter should be of type OutputBinding<T> , where T is a POJO or any native Java type.

Attributes and annotations

C#

For C# class libraries, use the EventHubAttribute attribute.

The attribute's constructor takes the name of the event hub and the name of an app setting that contains the connection string. For more information about these settings, see Output - configuration. Here's an EventHub attribute example:

[FunctionName("EventHubOutput")]
[return: EventHub("outputEventHubMessage", Connection = "EventHubConnectionAppSetting")]
public static string Run([TimerTrigger("0 */5 * * * *")] TimerInfo myTimer, ILogger log)
{
    ...
}

For a complete example, see Output - C# example.

C# Script

Attributes are not supported by C# Script.

JavaScript

Attributes are not supported by JavaScript.

Python

Attributes are not supported by Python.

Java

In the Java functions runtime library, use the EventHubOutput annotation on parameters whose value would be published to Event Hub. The parameter should be of type OutputBinding<T> , where T is a POJO or any native Java type.

Configuration

The following table explains the binding configuration properties that you set in the function.json file and the EventHub attribute.

function.json property	Attribute property	Description
type	n/a	Must be set to "eventHub".
direction	n/a	Must be set to "out". This parameter is set automatically when you create the binding in the Azure portal.
name	n/a	The variable name used in function code that represents the event.
path	EventHubName	Functions 1.x only. The name of the event hub. When the event hub name is also present in the connection string, that value overrides this property at runtime.
eventHubName	EventHubName	Functions 2.x and higher. The name of the event hub. When the event hub name is also present in the connection string, that value overrides this property at runtime.
connection	Connection	The name of an app setting that contains the connection string to the event hub's namespace. Copy this connection string by clicking the Connection Information button for the namespace, not the event hub itself. This connection string must have send permissions to send the message to the event stream. If you are using version 5.x or higher of the extension, instead of a connection string, you can provide a reference to a configuration section which defines the connection. See Connections.

[!INCLUDE app settings to local.settings.json]

Usage

C#

Default

You can use the following parameter types for the output binding of Event Hub:

string
byte[]
POCO
EventData - The default properties of EventData are provided in the for the Microsoft.Azure.EventHubs namespace.

Send messages by using a method parameter such as out string paramName. In C# script, paramName is the value specified in the name property of function.json. To write multiple messages, you can use ICollector<string> or IAsyncCollector<string> in place of out string.

Additional types

Apps using the 5.0.0 or higher version of the Event Hub extension use the EventData type in Azure.Messaging.EventHubs instead of the one in Microsoft.Azure.EventHubs namespace. This version drops support for the legacy Body type in favor of the following types:

EventBody

C# Script

Default

You can use the following parameter types for the output binding of Event Hub:

string
byte[]
POCO
EventData - The default properties of EventData are provided in the for the Microsoft.Azure.EventHubs namespace.

Send messages by using a method parameter such as out string paramName. In C# script, paramName is the value specified in the name property of function.json. To write multiple messages, you can use ICollector<string> or IAsyncCollector<string> in place of out string.

Additional types

Apps using the 5.0.0 or higher version of the Event Hub extension use the EventData type in Azure.Messaging.EventHubs instead of the one in Microsoft.Azure.EventHubs namespace. This version drops support for the legacy Body type in favor of the following types:

EventBody

JavaScript

Access the output event by using context.bindings.<name> where <name> is the value specified in the name property of function.json.

Python

There are two options for outputting an Event Hub message from a function:

Return value: Set the name property in function.json to $return. With this configuration, the function's return value is persisted as an Event Hub message.
Imperative: Pass a value to the set method of the parameter declared as an Out type. The value passed to set is persisted as an Event Hub message.

Java

There are two options for outputting an Event Hub message from a function by using the EventHubOutput annotation:

Return value: By applying the annotation to the function itself, the return value of the function is persisted as an Event Hub message.
Imperative: To explicitly set the message value, apply the annotation to a specific parameter of the type OutputBinding<T>, where T is a POJO or any native Java type. With this configuration, passing a value to the setValue method persists the value as an Event Hub message.

Exceptions and return codes

Binding	Reference
Event Hub	Operations Guide

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C#

C# Script

JavaScript

Python

Java

Attributes and annotations

C#

C# Script

JavaScript

Python

Java

Configuration

Usage

C#

Default

Additional types

C# Script

Default

Additional types

JavaScript

Python

Java

Exceptions and return codes

Files

functions-bindings-event-hubs-output.md

Latest commit

History

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Attributes and annotations

Configuration

Usage

Default

Additional types

Default

Additional types

Exceptions and return codes