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Tutorial: Python function with Azure Table Storage as output

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In this tutorial, you learn how to configure a Python function with Storage Table as output by completing the following tasks.

  • Use Visual Studio Code to create a Python function project.
  • Add a Storage Table output function binding.
  • Use Visual Studio Code to run the function locally.
  • Use the Azure CLI to create a connection between Azure Function and Storage Table with Service Connector.
  • Use Visual Studio to deploy your function.

An overview of the function project components in this tutorial:

Project Component Selection / Solution
Source Service Azure Function
Target Service Azure Storage Table
Function Binding HTTP trigger, Storage Table as Output
Local Project Auth Type Connection String
Cloud Function Auth Type Connection String

Warning

Microsoft recommends that you use the most secure authentication flow available. The authentication flow described in this procedure requires a very high degree of trust in the application, and carries risks that are not present in other flows. You should only use this flow when other more secure flows, such as managed identities, aren't viable.

Prerequisites

Create a Python function project

Follow the tutorial to create a local Azure Functions project, and provide the following information at the prompts:

Prompt Selection
Select a language Choose Python. (v1 programming language model)
Select a Python interpreter to create a virtual environment Choose your preferred Python interpreter. If an option isn't shown, type in the full path to your Python binary.
Select a template for your project's first function Choose HTTP trigger.
Provide a function name Enter TableStorageOutputFunc.
Authorization level Choose Anonymous, which lets anyone call your function endpoint. 

You have created a Python function project with an HTTP trigger.

Add a storage table output binding

Binding attributes are defined in the function.json file for a given function. To create a binding, right-click (Ctrl+click on macOS) the function.json file in your function folder and choose Add binding... . Follow the prompts to define the following binding properties for the new binding:

Prompt Value Description
Select binding direction out The binding is an output binding.
Select binding with direction... Azure Table Storage The binding is an Azure Storage table binding.
The name used to identify this binding in your code outMessage Name that identifies the binding parameter referenced in your code.
Table name in storage account where data will be written testTable The table name your function writes as output. Create a table named testTable in your storage account if it doesn't exist.
Select setting from "local.setting.json" Create new local app settings Select the Storage Account your function writes as output. Visual Studio Code retrieves its connection string for local project connection.

To check the binding was added successfully:

  1. Open the TableStorageOutputFunc/function.json file, check that a new binding with type: table and direction: out was added into this file.
  2. Open the local.settings.json file, check that a new key-value pair <your-storage-account-name>_STORAGE: <your-storage-account-connection-string> that contains your storage account connection string was added into this file.

After the binding is added, update your function codes to consume the binding by replacing TableStorageOutputFunc/__init__.py with the Python file here.

import logging
import uuid
import json
import azure.functions as func

def main(req: func.HttpRequest, outMessage: func.Out[str]) -> func.HttpResponse:

    rowKey = str(uuid.uuid4())
    data = {
        "Name": "Output binding message",
        "PartitionKey": "message",
        "RowKey": rowKey
    }

    outMessage.set(json.dumps(data))
    return func.HttpResponse(f"Message created with the rowKey: {rowKey}")

Run the function locally

Follow the tutorial to run the function locally and verify the table output.

  1. Select the Storage Account you chose when creating the Azure Function resource if you're prompted to connect to a storage account. This value is used for Azure Function runtime's. It isn't necessarily the same storage account you use for the output.
  2. To start the function locally, press <kbd>F5 </kbd> or select the Run and Debug icon in the left-hand side Activity bar.
  3. To verify the function can write to your table, right click Execute Function Now... on the function in the Visual Studio Code WORKSPACE view and check the function response. The response message should contain the rowKey that was written to the table.

Create a connection using Service Connector

In last step, you verified the function project locally. Now you'll learn how to configure the connection between the Azure Function and Azure Storage Table in the cloud, so that your function can write to your storage blob after being deployed to the cloud.

  1. Open the function.json file in your local project, change the value of the connection property in bindings to be AZURE_STORAGETABLE_CONNECTIONSTRING.
  2. Run the following Azure CLI command to create a connection between your Azure Function and your Azure Storage.
az functionapp connection create storage-table --source-id "<your-function-resource-id>" --target-id "<your-storage-table-resource-id>" --secret
  • --source-id format: /subscriptions/{subscription}/resourceG roups/{source_resource_group}/providers/Microsoft.Web/sites/{site}
  • --target-id format: /subscriptions/{subscription}/resourceGroups/{target_resource_group}/providers/Microsoft.Storage/storageAccounts/{account}/tableServices/default

You've created a Service Connector resource that configures an AZURE_STORAGETABLE_CONNECTIONSTRING variable in the function's App Settings. This app setting will then be consumed by the function binding to connect to the storage, so that the function can write to the storage table. You can learn more about how Service Connector helps Azure Functions connect to services.

Deploy your function to Azure

Now you can deploy your function to Azure and verify the storage table output binding works.

  1. Follow this Azure Functions tutorial to deploy your function to Azure.
  2. To verify the function can write to the table, right click Execute Function Now... on the function in the Visual Studio Code RESOURCES view, and check the function response. The response message should contain the rowKey the function just wrote to your table.

Troubleshoot

If there are any errors related with storage host, such as No such host is known (<acount-name>.table.core.windows.net:443), you need check whether the connection string you use to connect to Azure Storage contains the table endpoint or not. If it doesn't, go to Azure Storage portal, copy the connection string from the Access keys blade, and replace the values.

If this error happens when you start the project locally, check the local.settings.json file.

If it happens when you deploy your function to the cloud (in this case, Function deployment usually fails on Syncing triggers ), check your Function's App Settings.

Clean up resources

If you're not going to continue to use this project, delete the Function App resource you created earlier.

  1. In the Azure portal, open the Function App resource and select Delete.
  2. Enter the app name and select Delete to confirm.

Next steps

Read the articles below to learn more about Service Connector concepts and how it helps Azure Functions connect to other cloud services.

Learn about Service Connector concepts

Use Service Connector to connect Azure Functions to other cloud services