Enable offline development by using the Azure Cosmos DB emulator

Azure Cosmos DB is a globally distributed, multi-model database service offered by Microsoft Azure. It provides excellent support for building native applications that require high availability and scalable data storage. One of the key features of Azure Cosmos DB is the ability to enable offline development by using the Azure Cosmos DB emulator. In this article, we will explore how to utilize the emulator to develop applications in an offline environment.

What Is the Azure Cosmos DB Emulator?

The Azure Cosmos DB emulator is a locally run version of Azure Cosmos DB. It provides a development and testing environment that mirrors the functionality of the cloud-based Azure Cosmos DB service. By using the emulator, developers can create and run applications without incurring any cost associated with the actual usage of Azure Cosmos DB.

Getting Started with the Azure Cosmos DB Emulator

To get started with the Azure Cosmos DB emulator, you first need to download and install it on your local machine. The emulator is available for both Windows and Linux operating systems. Once installed, you can launch the emulator and start developing your applications.

When using the Azure Cosmos DB emulator, you interact with it using the same APIs and tools that you would use with the cloud-based Azure Cosmos DB service. The emulator supports SQL API, MongoDB API, Cassandra API, Gremlin API, and Table API. You can choose the API that aligns with your application requirements.

Enabling Offline Development with the Azure Cosmos DB Emulator

Let’s take a look at an example of how you can enable offline development using the Azure Cosmos DB emulator with the SQL API.

First, you need to create an instance of the DocumentClient class in your code. This class is part of the Azure Cosmos DB .NET SDK and provides the necessary methods to interact with the emulator.

You can then specify the endpoint URI and the authorization key for the emulator. These values can be obtained from the Azure Cosmos DB emulator’s user interface. Replace with the appropriate URI.

With the client instance created, you can now use it to perform CRUD (create, read, update, delete) operations on your data, just like you would with the cloud-based Azure Cosmos DB service.

For example, let’s say you want to query all documents from a collection named “myCollection”. You can use the following code:


const querySpec = {
query: "SELECT * FROM c",
parameters: []
};

client.queryDocuments(collectionLink, querySpec).toArray((err, results) => {
if (err) {
console.log("Error while querying documents", err);
} else {
console.log("Documents:", results);
}
});


This code executes a SQL query to fetch all documents from the “myCollection” collection and logs the results to the browser’s console.

Similarly, you can create, update, and delete documents using functions provided by the DocumentClient class.

Considerations and Conclusion

It’s important to note that the data stored in the Azure Cosmos DB emulator is local to your machine and does not persist across emulator instances. This means that if you stop and restart the emulator, the data will be reset. Therefore, it is recommended to back up your data regularly if needed.

In conclusion, the Azure Cosmos DB emulator is a powerful tool that enables offline development of native applications using Azure Cosmos DB. By leveraging the emulator, developers can create and test applications locally without incurring any cost. Whether you are using the SQL API, MongoDB API, Cassandra API, Gremlin API, or Table API, the emulator provides a consistent development experience. So go ahead and utilize the Azure Cosmos DB emulator to streamline your application development process.