DocumentDB with Azure Functions

You can do it using the Azure Portal. After you created the DocumentDB -

• Create new Azure Function.
• Go to the Integrate Tab.
• You can choose Azure Document DB as an output for your function.
• Choose your Document DB/Database Name/Collection you want to use.
• Document parameter name is the Output of your function.

For example

using System;

public static void Run(string input, out object document, TraceWriter log)
{
    log.Info($"C# manually triggered function called with input: {input}");
    document = new {
        text = $"I'm running in a C# function! {input}"
    };
}

you need to provide out object which is the same as you defined in the output tab.

You can just use the document client directly:

var endpoint = "https://XXXXX.documents.azure.com:443/";
var authKey = "XXXXX";

using (var client = new DocumentClient(new Uri(endpoint), authKey))
{
    var sqlCountQuery = "select value count(1) from c";
    IDocumentQuery<dynamic> query = client.CreateDocumentQuery<dynamic>(UriFactory.CreateDocumentCollectionUri("YOUR_DB_ID", "YOUR_COLLECTON_ID"), sqlCountQuery).AsDocumentQuery();
    ....
}

Azure Functions supports Document DB (Cosmos DB) out-of-the-box. You can just simply add an environment variable called AzureWebJobsDocumentDBConnectionString in V1 or AzureWebJobsCosmosDBConnectionString in V2.

Then just use a CosmosDBTrigger binding attribute for input binding like (in C# for example):

public static class UpsertProductCosmosDbTrigger
{
    [FunctionName("ProductUpsertCosmosDbTrigger")]
    public static void Run(
        [CosmosDBTrigger(
        // Those names come from the application settings.
        // Those names can come with both preceding % and trailing %.
        databaseName: "CosmosDbDdatabaseName",
        collectionName: "CosmosDbCollectionName",
        LeaseDatabaseName = "CosmosDbDdatabaseName",
        LeaseCollectionName = "CosmosDbLeaseCollectionName")] 
        IReadOnlyList<Document> input,

        TraceWriter log)
...

For output binding use DocumentDB output binding attribute in V1 and CosmosDB in V2 like:

[FunctionName("ProductUpsertHttpTrigger")]
public static async Task<HttpResponseMessage> Run(
    [HttpTrigger(AuthorizationLevel.Function, "post", Route = "products")] 
    HttpRequestMessage req,

    [DocumentDB(
    databaseName: "%CosmosDbDdatabaseName%",
    collectionName: "%CosmosDbCollectionName%")] IAsyncCollector<Product> collector,

    TraceWriter log)
...

I've written a blog post about this: https://blog.mexia.com.au/cosmos-db-in-azure-functions-v1-and-v2

var EndpointUrl = "EndpointUrl";
var PrimaryKey = "PrimaryKeyValue" 
this.client = new DocumentClient(new Uri(EndpointUrl), PrimaryKey);
Database database = await this.client.CreateDatabaseIfNotExistsAsync(new Database { Id = cosmoDbName });

you can get the End-point-URL and Primary-Key value from the azure portal in the keys section.

Assume C# has similar SDK like Java. The below is for Java

There are two ways you can connect to documentDB from an Azure function.

1. Using SDK

   DocumentClient documentClient = new DocumentClient( "SERVICE_ENDPOINT", "MASTER_KEY", ConnectionPolicy.GetDefault(), ConsistencyLevel.Session);

Refer - [https://learn.microsoft.com/en-us/azure/cosmos-db/sql-api-java-samples][1]. This has .Net Samples too.

2. Binding

   @FunctionName("CosmosDBStore") @CosmosDBOutput(name = "database", databaseName = "db_name", collectionName = "col_name", connectionStringSetting = "AzureCosmosDBConnection")

Please make sure you have a variable in the name of "AzureCosmosDBConnection" in your application settings and local.settings.json(if you want to test locally)

Refer - [https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-cosmosdb-v2][1]

The above link has C# example too.