functions-create-cosmos-db-triggered-function.md

title	description	ms.assetid	ms.topic	ms.date	ms.custom
Create a function triggered by Azure Cosmos DB	Use Azure Functions to create a serverless function that is invoked when data is added to a database in Azure Cosmos DB.	bc497d71-75e7-47b1-babd-a060a664adca	how-to	04/28/2020	cc996988-fb4f-47

Create a function triggered by Azure Cosmos DB

Learn how to create a function triggered when data is added to or changed in Azure Cosmos DB. To learn more about Azure Cosmos DB, see Azure Cosmos DB: Serverless database computing using Azure Functions.

:::image type="content" source="./media/functions-create-cosmos-db-triggered-function/quickstart-completed.png" alt-text="Azure Cosmos DB code":::

Prerequisites

To complete this tutorial:

• If you don't have an Azure subscription, create a free account before you begin.

Note

[!INCLUDE SQL API support only]

Sign in to Azure

Sign in to the Azure portal with your Azure account.

Create an Azure Cosmos DB account

You must have an Azure Cosmos DB account that uses the SQL API before you create the trigger.

[!INCLUDE cosmos-db-create-dbaccount]

Create an Azure Function app

[!INCLUDE Create function app Azure portal]

Next, you create a function in the new function app.

Create Azure Cosmos DB trigger

1. In your function app, select Functions from the left menu, and then select Add from the top menu.

2. On the New Function page, enter cosmos in the search field and then choose the Azure Cosmos DB trigger template.

   :::image type="content" source="./media/functions-create-cosmos-db-triggered-function/function-choose-cosmos.png" alt-text="Functions page in the Azure portal":::

3. Configure the new trigger with the settings as specified in the following table:

   Setting	Suggested value	Description
   New Function	Accept the default name	The name of the function.
   Cosmos DB account connection	Accept the default new name	Select New, the Database Account you created earlier, and then OK. This action creates an application setting for your account connection. This setting is used by the binding to connection to the database.
   Database name	Tasks	Name of the database that includes the collection to be monitored.
   Collection name	Items	Name of the collection to be monitored.
   Collection name for leases	leases	Name of the collection to store the leases.
   Create lease collection if it does not exist	Yes	Checks for existence of the lease collection and automatically creates it.

   :::image type="content" source="./media/functions-create-cosmos-db-triggered-function/functions-cosmosdb-trigger-settings.png" alt-text="Create the Azure Cosmos DB triggered function":::

4. Select Create Function.

   Azure creates the Cosmos DB trigger function.

5. To display the template-based function code, select Code + Test.

   :::image type="content" source="./media/functions-create-cosmos-db-triggered-function/function-cosmosdb-template.png" alt-text="Cosmos DB function template in C#":::

   This function template writes the number of documents and the first document ID to the logs.

Next, you connect to your Azure Cosmos DB account and create the Items container in the Tasks database.

Create the Items container

1. Open a second instance of the Azure portal in a new tab in the browser.

2. On the left side of the portal, expand the icon bar, type cosmos in the search field, and select Azure Cosmos DB.

   

3. Choose your Azure Cosmos DB account, then select the Data Explorer.

4. Under SQL API, choose Tasks database and select New Container.

   

5. In Add Container, use the settings shown in the table below the image.

   

   Setting	Suggested value	Description
   Database ID	Tasks	The name for your new database. This must match the name defined in your function binding.
   Container ID	Items	The name for the new container. This must match the name defined in your function binding.
   Partition key	/category	A partition key that distributes data evenly to each partition. Selecting the correct partition key is important in creating a performant container.
   Throughput	400 RU	Use the default value. If you want to reduce latency, you can scale up the throughput later.

6. Click OK to create the Items container. It may take a short time for the container to get created.

After the container specified in the function binding exists, you can test the function by adding items to this new container.

Test the function

1. Expand the new Items container in Data Explorer, choose Items, then select New Item.

   :::image type="content" source="./media/functions-create-cosmos-db-triggered-function/create-item-in-container.png" alt-text="Create an item in Items container":::

2. Replace the contents of the new item with the following content, then choose Save.

    {
        "id": "task1",
        "category": "general",
        "description": "some task"
    }
   

3. Switch to the first browser tab that contains your function in the portal. Expand the function logs and verify that the new document has triggered the function. See that the task1 document ID value is written to the logs.

   

4. (Optional) Go back to your document, make a change, and click Update. Then, go back to the function logs and verify that the update has also triggered the function.

Clean up resources

[!INCLUDE Next steps note]

Next steps

You have created a function that runs when a document is added or modified in your Azure Cosmos DB. For more information about Azure Cosmos DB triggers, see Azure Cosmos DB bindings for Azure Functions.

[!INCLUDE Next steps note]