Get started with Azure Cosmos DB for NoSQL using .NET

Article
10/12/2023

APPLIES TO: NoSQL

This article shows you how to connect to Azure Cosmos DB for NoSQL using the .NET SDK. Once connected, you can perform operations on databases, containers, and items.

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Prerequisites

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

Set up your project

Create the .NET console application

Create a new .NET application by using the dotnet new command with the console template.

dotnet new console

Import the Microsoft.Azure.Cosmos NuGet package using the dotnet add package command.

dotnet add package Microsoft.Azure.Cosmos

Build the project with the dotnet build command.

dotnet build

Connect to Azure Cosmos DB for NoSQL

To connect to the API for NoSQL of Azure Cosmos DB, create an instance of the CosmosClient class. This class is the starting point to perform all operations against databases. There are three core ways to connect to an API for NoSQL account using the CosmosClient class:

Connect with a API for NoSQL endpoint and read/write key
Connect with a API for NoSQL connection string
Connect with Microsoft Entra ID

Connect with an endpoint and key

The most common constructor for CosmosClient has two parameters:

Parameter	Example value	Description
`accountEndpoint`	`COSMOS_ENDPOINT` environment variable	API for NoSQL endpoint to use for all requests
`authKeyOrResourceToken`	`COSMOS_KEY` environment variable	Account key or resource token to use when authenticating

Retrieve your account endpoint and key

Create a shell variable for resourceGroupName.

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

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
)

Get the API for NoSQL endpoint URI for the account using the az cosmosdb show command.

az cosmosdb show \
    --resource-group $resourceGroupName \
    --name $accountName \
    --query "documentEndpoint"

Find the PRIMARY KEY from the list of keys for the account with the az-cosmosdb-keys-list command.

az cosmosdb keys list \
    --resource-group $resourceGroupName \
    --name $accountName \
    --type "keys" \
    --query "primaryMasterKey"

Record the URI and PRIMARY KEY values. You'll use these credentials later.

Create a shell variable for RESOURCE_GROUP_NAME.

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

Use the Get-AzCosmosDBAccount cmdlet to retrieve the name of the first Azure Cosmos DB account in your resource group and store it in the ACCOUNT_NAME shell variable.

# Retrieve most recently created account name
$parameters = @{
    ResourceGroupName = $RESOURCE_GROUP_NAME
}
$ACCOUNT_NAME = (
    Get-AzCosmosDBAccount @parameters |
        Select-Object -Property Name -First 1
).Name

Get the API for NoSQL endpoint URI for the account using the Get-AzCosmosDBAccount cmdlet.

$parameters = @{
    ResourceGroupName = $RESOURCE_GROUP_NAME
    Name = $ACCOUNT_NAME
}
Get-AzCosmosDBAccount @parameters |
    Select-Object -Property "DocumentEndpoint"

Find the PRIMARY KEY from the list of keys for the account with the Get-AzCosmosDBAccountKey cmdlet.

$parameters = @{
    ResourceGroupName = $RESOURCE_GROUP_NAME
    Name = $ACCOUNT_NAME
    Type = "Keys"
}    
Get-AzCosmosDBAccountKey @parameters |
    Select-Object -Property "PrimaryMasterKey"

Record the URI and PRIMARY KEY values. You'll use these credentials later.

To use the URI and PRIMARY KEY values within your .NET code, persist them to new environment variables on the local machine running the application.

Windows
Linux / macOS

$env:COSMOS_ENDPOINT = "<cosmos-account-URI>"
$env:COSMOS_KEY = "<cosmos-account-PRIMARY-KEY>"

export COSMOS_ENDPOINT="<cosmos-account-URI>"
export COSMOS_KEY="<cosmos-account-PRIMARY-KEY>"

Create CosmosClient with account endpoint and key

Create a new instance of the CosmosClient class with the COSMOS_ENDPOINT and COSMOS_KEY environment variables as parameters.

// New instance of CosmosClient class using an endpoint and key string
using CosmosClient client = new(
    accountEndpoint: Environment.GetEnvironmentVariable("COSMOS_ENDPOINT")!,
    authKeyOrResourceToken: Environment.GetEnvironmentVariable("COSMOS_KEY")!
);

Connect with a connection string

Another constructor for CosmosClient only contains a single parameter:

Parameter	Example value	Description
`accountEndpoint`	`COSMOS_ENDPOINT` environment variable	API for NoSQL endpoint to use for all requests
`connectionString`	`COSMOS_CONNECTION_STRING` environment variable	Connection string to the API for NoSQL account

Retrieve your account connection string

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
)

Find the PRIMARY CONNECTION STRING from the list of connection strings for the account with the az-cosmosdb-keys-list command.

az cosmosdb keys list \
    --resource-group $resourceGroupName \
    --name $accountName \
    --type "connection-strings" \
    --query "connectionStrings[?description == \`Primary SQL Connection String\`] | [0].connectionString"

Use the Get-AzCosmosDBAccount cmdlet to retrieve the name of the first Azure Cosmos DB account in your resource group and store it in the ACCOUNT_NAME shell variable.

# Retrieve most recently created account name
$parameters = @{
    ResourceGroupName = $RESOURCE_GROUP_NAME
}
$ACCOUNT_NAME = (
    Get-AzCosmosDBAccount @parameters |
        Select-Object -Property Name -First 1
).Name

Find the PRIMARY CONNECTION STRING from the list of 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 SQL Connection String" -First 1

To use the PRIMARY CONNECTION STRING value within your .NET code, persist it to a new environment variable on the local machine running the application.

Windows
Linux / macOS

$env:COSMOS_CONNECTION_STRING = "<cosmos-account-PRIMARY-CONNECTION-STRING>"

export COSMOS_CONNECTION_STRING="<cosmos-account-PRIMARY-CONNECTION-STRING>"

Create CosmosClient with connection string

Create a new instance of the CosmosClient class with the COSMOS_CONNECTION_STRING environment variable as the only parameter.

// New instance of CosmosClient class using a connection string
using CosmosClient client = new(
    connectionString: Environment.GetEnvironmentVariable("COSMOS_CONNECTION_STRING")!
);

Connect using the Microsoft identity platform

To connect to your API for NoSQL account using the Microsoft identity platform and Microsoft Entra ID, use a security principal. The exact type of principal will depend on where you host your application code. The table below serves as a quick reference guide.

Where the application runs	Security principal
Local machine (developing and testing)	User identity or service principal
Azure	Managed identity
Servers or clients outside of Azure	Service principal

Import Azure.Identity

The Azure.Identity NuGet package contains core authentication functionality that is shared among all Azure SDK libraries.

Import the Azure.Identity NuGet package using the dotnet add package command.

dotnet add package Azure.Identity

Rebuild the project with the dotnet build command.

dotnet build

In your code editor, add using directives for Azure.Core and Azure.Identity namespaces.

using Azure.Core;
using Azure.Identity;

Create CosmosClient with default credential implementation

If you're testing on a local machine, or your application will run on Azure services with direct support for managed identities, obtain an OAuth token by creating a DefaultAzureCredential instance.

For this example, we saved the instance in a variable of type TokenCredential as that's a more generic type that's reusable across SDKs.

// Credential class for testing on a local machine or Azure services
TokenCredential credential = new DefaultAzureCredential();

Create a new instance of the CosmosClient class with the COSMOS_ENDPOINT environment variable and the TokenCredential object as parameters.

// New instance of CosmosClient class using a connection string
using CosmosClient client = new(
    accountEndpoint: Environment.GetEnvironmentVariable("COSMOS_ENDPOINT")!,
    tokenCredential: credential
);

Create CosmosClient with a custom credential implementation

If you plan to deploy the application out of Azure, you can obtain an OAuth token by using other classes in the Azure.Identity client library for .NET. These other classes also derive from the TokenCredential class.

For this example, we create a ClientSecretCredential instance by using client and tenant identifiers, along with a client secret.

// Custom credential class for servers and clients outside of Azure
TokenCredential credential = new ClientSecretCredential(
    tenantId: Environment.GetEnvironmentVariable("AAD_TENANT_ID")!,
    clientId: Environment.GetEnvironmentVariable("AAD_CLIENT_ID")!,
    clientSecret: Environment.GetEnvironmentVariable("AAD_CLIENT_SECRET")!,
    options: new TokenCredentialOptions()
);

You can obtain the client ID, tenant ID, and client secret when you register an application in Microsoft Entra ID. For more information about registering Microsoft Entra applications, see Register an application with the Microsoft identity platform.

Create a new instance of the CosmosClient class with the COSMOS_ENDPOINT environment variable and the TokenCredential object as parameters.

// New instance of CosmosClient class using a connection string
using CosmosClient client = new(
    accountEndpoint: Environment.GetEnvironmentVariable("COSMOS_ENDPOINT")!,
    tokenCredential: credential
);

Build your application

As you build your application, your code will primarily interact with four types of resources:

The API for NoSQL account, which is the unique top-level namespace for your Azure Cosmos DB data.
Databases, which organize the containers in your account.
Containers, which contain a set of individual items in your database.
Items, which represent a JSON document in your container.

The following diagram shows the relationship between these resources.

Diagram of the Azure Cosmos DB hierarchy including accounts, databases, containers, and items.

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

Class	Description
`CosmosClient`	This class provides a client-side logical representation for the Azure Cosmos DB service. The client object is used to configure and execute requests against the service.
`Database`	This class is a reference to a database that may, or may not, exist in the service yet. The database is validated server-side when you attempt to access it or perform an operation against it.
`Container`	This class is a reference to a container that also may not exist in the service yet. The container 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.

Guide	Description
Create a database	Create databases
Create a container	Create containers
Read an item	Point read a specific item
Query items	Query multiple items

Next steps

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

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