Azure Cosmos db and functions javascript sdk - how to read document async?

Question

I have the following code in an apollo resolver:

Mutation: {
    addChannel: (root, args) => {
      client.readDocument("website", {}, (x) => {
        return { id: "Test", name: "Test Channel " + args.name }
      });
    },

where client is a document client:

var DocumentClient = require('documentdb').DocumentClient;

When it's called I'd like to wait on client.readDocument to finish and give me a return value that I will return (the example above is super simple and won't do that)

The problem I have is readDocument does something asynchronously in the background but the function isn'ta sync so I can't await it, so the function immediately falls through before the callback has a chance to finish. After the return data is sent (which is undefined) the callback function (x)=>{...} occurs..

Answer 1

Three solutions I can think of here (which to use will depend on your exact situation):

1. v2 of the Cosmos DB API has async/await support so you can use that instead of the callback.
2. Wrap the callback code in a promise and await the promise.
3. Use a non-async Azure Function and return the result with context.done(result) at the end of the callback.

Answer 2

I would suggest you move towards the v2 version of the Javascript API: https://github.com/Azure/azure-cosmos-js

That way you can use the fluent path to the items and use const { body: readDoc } = await item.read(); to read an item async.

You can find multiple samples on how this is done here

Answer 3

The nature of your code doesn't fit with the callback model that readDocument follows therefore you have no mechanism to pass the document back out from addChannel .

Presuming you don't need to do any pre-processing to the document beforehand, you could use a combination of promises and the async / await syntax eg

addChannel: (root, arg) => 
  new Promise((resolve, reject) => 
    client.readDocument("website", {}, (err, x) => 
      err ? reject(err) : resolve(x)
    )
  );
}

Then to "wait" on the document before executing other code

const doc = await obj.addChannel(...);
// use doc

Note - await can only be used within a function marked as async