best practice for function app service bus trigger and blobinput attribute

Question

this is our function declaration:

stack error details:

Error converting 1 input parameters for Function 'DistributeBusinessPartner': Cannot convert input parameter 'messageIn' to type 'Azure.Messaging.ServiceBus.ServiceBusReceivedMessage' from type 'System.String'. Error:System.NotSupportedException: Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported. Type 'Azure.Messaging.ServiceBus.ServiceBusReceivedMessage'. Path: $ | LineNumber: 0 | BytePositionInLine: 1.

then based on the error message, we fixed the issue by changing the function declaration like below:

but if we change messageIn to string type, meesageIn will only receive the message body instead of the ServiceBusReceivedMessage object, we wanted to confirm if there's a way to let us use ServiceBusReceivedMessage and BlobInput correctly at the same time, or what's the best practice of this case? thank you very much.

https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-service-bus-trigger?tabs=python-v2%2Cisolated-process%2Cnodejs-v4%2Cextensionv5&pivots=programming-language-csharp#example

Answer 1

Hello @Wang Meihua

The error message suggests that the ServiceBusReceivedMessage object does not have a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with JsonConstructorAttribute, which is required for deserialization.

To use ServiceBusReceivedMessage and BlobInput correctly at the same time, you can modify your function declaration to include both parameters, like this:

public static void Run( [ServiceBusTrigger("myqueue")]
ServiceBusReceivedMessage messageIn, [Blob("mycontainer/{MessageId}", FileAccess.Read)] Stream myBlob)
{ 
	// Your code here 
}

This will allow you to receive both the ServiceBusReceivedMessage object and the blob input in your function. You can then use the properties of the ServiceBusReceivedMessage object to process the message, and the contents of the blob to perform any necessary operations. Alternatively, you can also modify your function to receive the message body as a string, and then use the ServiceBusReceivedMessage constructor to create a new instance of the object, like this:

public static void Run( [ServiceBusTrigger("myqueue")] string messageBody, [Blob("mycontainer/{MessageId}", FileAccess.Read)] Stream myBlob)
{ 
	ServiceBusReceivedMessage messageIn = new
 		ServiceBusReceivedMessage(Encoding.UTF8.GetBytes(messageBody));
	// Your code here
 }

This will allow you to receive the message body as a string, and then create a new instance of the ServiceBusReceivedMessage object using the constructor that takes a byte array.

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