I'm dealing with a code base where we have eventHub which uses cardinality many and datatype as string written in Azure function v3. Now I'm upgrading it to Azure function v4 format which lacks the property datatype and causing error.

System.Private.CoreLib: Exception while executing function: Functions.FnMessageConsumer. Microsoft.Azure.WebJobs.Host: Exception binding parameter 'eventHubTrigger64714af0d5'. Microsoft.Azure.WebJobs.Host: Binding parameters to complex objects (such as 'Object') uses Json.NET serialization. Change the queue payload to be valid json. The JSON parser failed: Unexpected character encountered while parsing value: e. Path '', line 0, position 0.

I'm expecting a string array as message.

My code is similar to following

app.eventHub('SampleFn', {
eventHubName: '%VENTHUB_NAME%',
consumerGroup: '$Default',
connection: 'EVENTHUB_CONNECTION_STRING',
cardinality: 'many',
handler: new Controller().function // my controller function reference
});

I tried following also

app.eventHub('FnMessageConsumer', {
    eventHubName: '%MESSAGE_EVENTHUB_NAME%',
    consumerGroup: '$Default',
    connection: 'EVENTHUB_CONNECTION_STRING',
    cardinality: 'many',
    //@ts-ignore
    dataType:"string",
    handler: new MessageConsumerController().function
});

Adding dataType:"string" worked, but this was not there in the typedefinition for eventHub. Is there any other way to archieve the result? or is this correct by ingoring the typecheck

I'm dealing with a code base where we have eventHub which uses cardinality many and datatype as string written in Azure function v3. Now I'm upgrading it to Azure function v4 format which lacks the property datatype and causing error.

System.Private.CoreLib: Exception while executing function: Functions.FnMessageConsumer. Microsoft.Azure.WebJobs.Host: Exception binding parameter 'eventHubTrigger64714af0d5'. Microsoft.Azure.WebJobs.Host: Binding parameters to complex objects (such as 'Object') uses Json.NET serialization. Change the queue payload to be valid json. The JSON parser failed: Unexpected character encountered while parsing value: e. Path '', line 0, position 0.

I'm expecting a string array as message.

My code is similar to following

app.eventHub('SampleFn', {
eventHubName: '%VENTHUB_NAME%',
consumerGroup: '$Default',
connection: 'EVENTHUB_CONNECTION_STRING',
cardinality: 'many',
handler: new Controller().function // my controller function reference
});

I tried following also

app.eventHub('FnMessageConsumer', {
    eventHubName: '%MESSAGE_EVENTHUB_NAME%',
    consumerGroup: '$Default',
    connection: 'EVENTHUB_CONNECTION_STRING',
    cardinality: 'many',
    //@ts-ignore
    dataType:"string",
    handler: new MessageConsumerController().function
});

Adding dataType:"string" worked, but this was not there in the typedefinition for eventHub. Is there any other way to archieve the result? or is this correct by ingoring the typecheck

• typescript
• azure-functions
• azure-eventhub

• Remove dataType: "string" and use messages.map(msg => msg.toString()) in the handler to correctly parse the string array. – Dasari Kamali Commented 6 hours ago
• When dataType: String is removed, azure throws an exception even before reaching the handler function. – Raj Kiran R Commented 4 hours ago

1 Answer 1

To handle Event Hub messages in Azure Functions v4 without using the deprecated dataType property, I used the below EventHubTrigger function in TypeScript. It handles messages of unknown types by parsing each message to a string using messages.map(msg => msg?.toString?.() ?? String(msg));.

eventHubTrigger1.ts :

import { app, InvocationContext } from "@azure/functions";

export async function eventHubTrigger1(messages: unknown | unknown[], context: InvocationContext): Promise<void> {
    if (Array.isArray(messages)) {
        context.log(`Event hub function processed ${messages.length} messages`);

        const parsedMessages = messages.map(msg => msg?.toString?.() ?? String(msg));

        for (const parsedMessage of parsedMessages) {
            try {
                context.log('Processed Event Hub message:', parsedMessage);
            } catch (error) {
                context.error('Error processing message:', error);
            }
        }
    } else {
        try {
            const parsedMessage = messages?.toString?.() ?? String(messages);
            context.log('Processed single Event Hub message:', parsedMessage);
        } catch (error) {
            context.error('Error processing single message:', error);
        }
    }
}

app.eventHub('eventHubTrigger1', {
    connection: 'EventHubConnString',
    eventHubName: '<eventhubName>',
    cardinality: 'many',
    handler: eventHubTrigger1
});

I sent a message to the Event Hub in the Azure portal.

Output :

The Event Hub trigger function with TypeScript in the v4 model ran successfully and received the message as shown below.