Azure Functions Input Bindings Overview

Input bindings provide a way to declaratively bind to external data sources in Azure Functions. They simplify the process of accessing data by abstracting away the underlying SDKs and connection management. This allows you to focus on your function's core logic rather than the intricacies of data retrieval.

What are Input Bindings?

Input bindings are configured in your function's `function.json` file (or via attributes in code for compiled languages). They define how your function receives data from a service, such as a queue, a blob storage container, a database, or an HTTP request. When the function is triggered, the input binding automatically fetches the specified data and makes it available as a parameter in your function code.

Benefits of Using Input Bindings

Simplicity: Reduces boilerplate code for data access.
Declarative: Configuration-driven, making it easy to understand data dependencies.
Flexibility: Supports a wide range of Azure and third-party services.
Type Safety: Data is often automatically deserialized into appropriate types.
Performance: Optimized for efficient data retrieval.

Common Input Binding Types

Azure Functions offers a rich set of built-in input bindings. Here are a few examples:

Blob Storage Input Binding

Retrieve the content of a blob from Azure Blob Storage.

                
{
  "bindings": [
    {
      "name": "myBlob",
      "type": "blob",
      "direction": "in",
      "path": "samples-workitems/{name}",
      "connection": "AzureWebJobsStorage"
    }
  ]
}
                
            

In your function code, `myBlob` would be a parameter holding the blob's content. The `path` property specifies the container and blob name pattern, and `connection` refers to an app setting containing the storage account connection string.

Cosmos DB Input Binding

Retrieve documents from an Azure Cosmos DB collection.

                
{
  "bindings": [
    {
      "name": "user",
      "type": "cosmosDB",
      "direction": "in",
      "databaseName": "samples",
      "collectionName": "users",
      "id": "{id}",
      "partitionKey": "{partitionKey}",
      "connectionStringSetting": "CosmosDBConnection"
    }
  ]
}
                
            

This binding fetches a specific document identified by `id` and optionally `partitionKey` from the `users` collection in the `samples` database.

Service Bus Queue Input Binding

Retrieve a message from an Azure Service Bus Queue.

                
{
  "bindings": [
    {
      "name": "message",
      "type": "serviceBusTrigger",
      "direction": "in",
      "queueName": "myqueue",
      "connection": "ServiceBusConnection"
    }
  ]
}
                
            

While this is technically a trigger, it acts as an input mechanism to receive queue messages. The `message` parameter will contain the content of the queue message.

How to Configure Input Bindings

Input bindings are typically defined in the `function.json` file located in the root of your function's folder. For each binding, you specify:

name: The name of the parameter in your function code.
type: The type of the binding (e.g., blob, cosmosDB, queue).
direction: Set to in for input bindings.
Service-specific properties: Such as path, databaseName, queueName, connection, etc.

Learn More

For a comprehensive list of supported bindings and detailed configuration options, please refer to the official Azure Functions bindings documentation.