Get started with Azure Cosmos DB for MongoDB using .NET

Article
11/17/2022

APPLIES TO: MongoDB

This article shows you how to connect to Azure Cosmos DB for MongoDB using .NET Core and the relevant NuGet packages. Once connected, you can perform operations on databases, collections, and documents.

Note

The example code snippets are available on GitHub as a .NET Core project.

API for MongoDB reference documentation | MongoDB Package (NuGet)

Prerequisites

An Azure account with an active subscription. Create an account for free.
.NET 6.0
Azure Command-Line Interface (CLI) or Azure PowerShell
Azure Cosmos DB for MongoDB resource

Create a new .NET Core app

Create a new .NET Core application in an empty folder using your preferred terminal. For this scenario, you'll use a console application. Use the dotnet new command to create and name the console app.
```
dotnet new console -o app
```
Add the MongoDB NuGet package to the console project. Use the dotnet add package command specifying the name of the NuGet package.
```
dotnet add package MongoDB.Driver
```
To run the app, use a terminal to navigate to the application directory and run the application.
```
dotnet run
```

Connect to Azure Cosmos DB for MongoDB with the MongoDB native driver

To connect to Azure Cosmos DB with the MongoDB native driver, create an instance of the MongoClient class. This class is the starting point to perform all operations against MongoDb databases. The most common constructor for MongoClient accepts a connection string, which you can retrieve using the following steps:

Get resource name

Create a shell variable for resourceGroupName.

# Variable for resource group name
resourceGroupName="msdocs-cosmos"

Use the az cosmosdb list command to retrieve the name of the first Azure Cosmos DB account in your resource group and store it in the accountName shell variable.

# Retrieve most recently created account name
accountName=$(
    az cosmosdb list \
        --resource-group $resourceGroupName \
        --query "[0].name" \
        --output tsv
)

Create a shell variable for RESOURCE_GROUP_NAME.

# Variable for resource group name
$RESOURCE_GROUP_NAME = "msdocs-cosmos"

Use the Get-AzCosmosDBAccountKey cmdlet to retrieve the name of the first Azure Cosmos DB account in your resource group and store it in the accountName shell variable.
```
# Get the name of the first Azure Cosmos DB account in your resource group
$ACCOUNT_NAME = (Get-AzCosmosDBAccount -ResourceGroupName $RESOURCE_GROUP_NAME)[0].Name
```

Retrieve your connection string

Find the API for MongoDB connection string from the list of connection strings for the account with the az cosmosdb keys list command.
```
az cosmosdb keys list --type connection-strings \
    --resource-group $resourceGroupName \
    --name $accountName 
```
Record the PRIMARY KEY values. You'll use these credentials later.

Find the CONNECTION STRING from the list of keys and connection strings for the account with the Get-AzCosmosDBAccountKey cmdlet.

$parameters = @{
    ResourceGroupName = $RESOURCE_GROUP_NAME
    Name = $ACCOUNT_NAME
    Type = "ConnectionStrings"
}    
Get-AzCosmosDBAccountKey @parameters |
    Select-Object -Property "Primary MongoDB Connection String"

Record the CONNECTION STRING value. You'll use these credentials later.

Configure environment variables

To use the CONNECTION STRING values within your code, set this value in the local environment running the application. To set the environment variable, use your preferred terminal to run the following commands:

$env:COSMOS_CONNECTION_STRING = "<cosmos-connection-string>"

export COSMOS_CONNECTION_STRING="<cosmos-connection-string>"

A .env file is a standard way to store environment variables in a project. Create a .env file in the root of your project. Add the following lines to the .env file:

COSMOS_CONNECTION_STRING="<cosmos-connection-string>"

Create MongoClient with connection string

Define a new instance of the MongoClient class using the constructor and the connection string variable you set previously.

// New instance of CosmosClient class
var client = new MongoClient(Environment.GetEnvironmentVariable("COSMOS_CONNECTION_STRING"));

var settings = client.Settings;

Console.WriteLine(settings.Server.Host);

Use the MongoDB client classes with Azure Cosmos DB for API for MongoDB

Before you start building the application, let's look into the hierarchy of resources in Azure Cosmos DB. Azure Cosmos DB has a specific object model used to create and access resources. The Azure Cosmos DB creates resources in a hierarchy that consists of accounts, databases, collections, and docs.

Diagram of the Azure Cosmos DB DB hierarchy including accounts, databases, collections, and docs.

Each type of resource is represented by one or more associated C# classes. Here's a list of the most common classes:

Class	Description
`MongoClient`	This class provides a client-side logical representation for the API for MongoDB layer on Azure Cosmos DB. The client object is used to configure and execute requests against the service.
`MongoDatabase`	This class is a reference to a database that may, or may not, exist in the service yet. The database is validated or created server-side when you attempt to perform an operation against it.
`Collection`	This class is a reference to a collection that also may not exist in the service yet. The collection is validated server-side when you attempt to work with it.

The following guides show you how to use each of these classes to build your application and manage data.

Guide:

Next steps

Now that you've connected to an API for MongoDB account, use the next guide to create and manage databases.

Create a database in Azure Cosmos DB for MongoDB using .NET