Implement an update by using a patch operation

To implement an update by using a patch operation in the context of designing and implementing native applications using Microsoft Azure Cosmos DB, you can utilize the available APIs and SDKs provided by Cosmos DB. In this article, we will explore how to perform a patch operation on a document using the Cosmos DB SQL API.

Partial Updates with Patch API

Cosmos DB provides the capability to perform partial updates on documents stored in its collections using the Patch API. The Patch API allows you to update specific properties of a document without fetching and replacing the entire document. This can be more efficient and reduces network round trips when you only need to update a few properties.

To demonstrate the patch operation, let’s assume you have already set up your Cosmos DB account and created a database and a collection called “Products.” In this collection, we have documents representing different products with properties like “productId,” “productName,” and “price.”

Initializing the CosmosClient

First, you need to obtain the URI and the access key for your Cosmos DB account. You can find these values in the Azure portal or by using the Azure CLI.

Next, you will need to choose a programming language and an SDK to interact with Cosmos DB. For the purpose of this article, we will use JavaScript and the Node.js SDK.

To begin, you need to install the Azure Cosmos package using npm:

npm install @azure/cosmos

Once you have the package installed, you can create a JavaScript file, e.g., “patch-example.js,” and initialize the CosmosClient with your Cosmos DB account details:

const { CosmosClient } = require(“@azure/cosmos”);

const endpoint = ““;
const key = ““;

const client = new CosmosClient({ endpoint, key });

Performing the Patch Operation

Now, let’s assume we want to update the price of a specific product with a known “productId.” We can use the Patch API to perform this partial update:

const databaseId = “your-database-id”;
const containerId = “your-container-id”;

async function patchProductPrice(productId, newPrice) {
const container = client.database(databaseId).container(containerId);
const product = await container.item(productId).read();

product.resource.price = newPrice;

const updatedProduct = await container.item(productId).replace(product.resource);
console.log(`Product price updated successfully: ${updatedProduct.resource.price}`);
}

patchProductPrice(“123”, 9.99);

In the above example, we first retrieve the document with the specified “productId” using the item() and read() methods. Then, we modify the price property with the new value. Finally, we use the replace() method to update the document in Cosmos DB.

By using the Patch API, we were able to perform a partial update on a document without fetching and replacing the entire document. This can be particularly useful when dealing with large documents or when you have a need for efficiency in your application.

Remember to replace the placeholders (““, ““, “your-database-id”, and “your-container-id”) with the actual values relevant to your Cosmos DB account, database, and container.

In this article, we explored how to implement an update by using a patch operation in Microsoft Azure Cosmos DB. We utilized the available SDKs and APIs provided by Cosmos DB to perform a partial update on a document stored in a collection. This enables us to efficiently update specific properties without the need to fetch and replace the entire document.