Interacting with CosmosDB from a serverless application can be achieved with very few lines of code using C#.
Pre-requisites:
- A CosmosDB resource
- An Azure Functions resource
- An input binding (the CosmosDB resource) is required for read operations, while an output binding (the CosmosDB resource) is needed for the write operations. For each operation, I share the specific function.json required.
Considerations:
- In each code there is a model (class) of your data. In our example, we are using a Student class.
- Each operation is an HTTP trigger.
Let’s go!
Operation 1. Retrieving data:
function.json is available here.
using System.Net;
using Microsoft.AspNetCore.Mvc;
public static async Task<IActionResult> Run(HttpRequest req, IEnumerable<Student> inputDocument, ILogger log)
{
var students = (List<Student>) inputDocument;
return new OkObjectResult(students);
}
Comments:
No “special” library/SDK is required to read from CosmosDB since this is handled by the binding in function.json!
Testing:
Simply send a GET request to the URL provided by Azure Functions and you’ll get your data:
Operation 2. Adding data:
function.json is available here
#r "Newtonsoft.Json"
using Microsoft.AspNetCore.Mvc;
using Newtonsoft.Json;
public static IActionResult Run(HttpRequest req, out object outputDocument, ILogger log)
{
var body = new StreamReader(req.Body).ReadToEnd();
dynamic data = JsonConvert.DeserializeObject(body);
outputDocument = new
{
id = data.id,
faculty = data.faculty,
Name = data.Name,
Semester = data.Semester
};
return (ActionResult)new OkResult();
}
Comments:
The return statement writes new data in CosmosDB since we set that resource as an output binding (see the associated function.json).
Testing:
Send a POST request to the URL provided by Azure Functions including the new data (Student object) in the Body.
Result is 200 OK =)
Operation 3. Updating data:
function.json is available here
#r "Newtonsoft.Json"
#r "Microsoft.Azure.DocumentDB.Core"
#r "Microsoft.Azure.WebJobs.Extensions.CosmosDB"
using System.Net;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Primitives;
using Newtonsoft.Json;
using Microsoft.Azure.Documents.Client;
public static async Task<IActionResult> Run(
HttpRequest req,
[CosmosDB(ConnectionStringSetting = "universitylb7_DOCUMENTDB")] DocumentClient outputDocument,
ILogger log, string id, string faculty)
{
string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
var updated = JsonConvert.DeserializeObject<Student>(requestBody);
var option = new FeedOptions { EnableCrossPartitionQuery = true };
var collectionUri = UriFactory.CreateDocumentCollectionUri("studentsdb", "students");
var document = outputDocument.CreateDocumentQuery(collectionUri, option).Where(t => t.Id == id)
.AsEnumerable().FirstOrDefault();
if (document == null)
{
return new NotFoundResult();
}
document.SetPropertyValue("Name", updated.Name);
document.SetPropertyValue("Semester", updated.Semester);
await outputDocument.ReplaceDocumentAsync(document);
return new OkResult();
}
Comments:
To update (and delete) we need the libraries ( Microsoft.Azure.DocumentDB.Core and Microsoft.Azure.WebJobs.Extensions.CosmosDB) since we need to search and then replace the document with the latest content.
Moreover, in the function.json you will see that a route is specified: it means that the URL must include the id and partition key of the document we want to update (the combination of both elements must be unique in a collection). And of course, you will include the new data in the Body request.
Once again, the result is a nice 200 OK.
function.json is available here
#r "Newtonsoft.Json"
#r "Microsoft.Azure.DocumentDB.Core"
#r "Microsoft.Azure.WebJobs.Extensions.CosmosDB"
using System.Net;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.Documents.Client;
public static async Task<IActionResult> Run(
HttpRequest req,
[CosmosDB(ConnectionStringSetting = "universitylb7_DOCUMENTDB")] DocumentClient outputDocument,
ILogger log, string id, string faculty)
{
var option = new FeedOptions { EnableCrossPartitionQuery = true };
var collectionUri = UriFactory.CreateDocumentCollectionUri("studentsdb", "students");
var document = outputDocument.CreateDocumentQuery(collectionUri, option).Where(t => t.Id == id).AsEnumerable().FirstOrDefault();
if (document == null)
{
return new NotFoundResult();
}
await outputDocument.DeleteDocumentAsync(document.SelfLink, new RequestOptions
{
PartitionKey = new Microsoft.Azure.Documents.PartitionKey(faculty)
});
return new OkResult();
}
Comments:
The code to delete is quite similar to the update one, except we don’t replace here (but delete) the document.
Testing:
Just include the id and faculty in the URL query parameters.
Bye-bye data!
And with that, we have set a serverless API that can interact with CosmosDB.
I hope that this blog post was interesting and useful for you. I invite you to visit my blog for more technical posts about Xamarin, Azure, and the .NET ecosystem. I write in Spanish language =)
Thanks for your time, and enjoy the rest of the C# Advent Calendar publications!
See you next time,
Luis
This blog featured as part of Azure Week. Find more great Azure content here.
About the Author:
Mexican Microsoft #MVP in AI and Dev Tech | PhD student @UniverzitaTBatiXamarin Dev #Lince@ItcelayaOficial | Writing my own story #FlyHigh
Reference:
Beltran, L. (2021). C# Azure Functions to access CosmosDB. Available at: https://dev.to/icebeam7/c-azure-functions-to-access-cosmosdb-5632 [Accessed: 30th June 2022].
