Calling Async C# Method

[charles-slc]

I've read through everything I can find, including
#598
and #182

For (silly) reasons, we are trying to use the C# Dynamo Client from JS.

We have a C# method that looks like so:

var script = File.ReadAllText("TestScript.js");
var client = new AmazonDynamoDBClient();
var engine = new V8ScriptEngine(V8ScriptEngineFlags.EnableStringifyEnhancements | V8ScriptEngineFlags.EnableTaskPromiseConversion);

engine.AddHostObject("DynamoClient", client);
engine.AddHostType("DynamoTable", typeof(Table));
engine.AddHostType("DynamoDocument", typeof(Amazon.DynamoDBv2.DocumentModel.Document));
engine.AddHostType("DynamoDbSerializationHelpers", typeof(DynamoDbSerializationHelpers));
engine.AddHostType("Console", typeof(Console));

engine.Execute(script);
var results = engine.Invoke("PostDDB");

A "working" TestScript.js looks like so

function PostDDB() {
   // code that builds up data
    let table = DynamoTable.LoadTable(DynamoClient, "charles-test");
    let itemJson = JSON.stringify(data);
    let docItem = DynamoDocument.FromJson(itemJson);

    let results = table.PutItemAsync(docItem).Result;
    return results;
}

But I know that using .Result isn't a (normally) good idea.

I've tried various things, but can't seem to get it to work.

[ClearScriptLib]

Hi @charles-slc,

But I know that using .Result isn't a (normally) good idea.

Since you're enabling task-promise conversion, why not simply use await?

async function PostDDB() {
    // ...
    let results = await table.PutItemAsync(docItem);
    return results;
}

And then:

engine.Execute(script);
var results = await (Task<object>)engine.Invoke("PostDDB");

Good luck!

[charles-slc]

That ended up with results in the C# method being null...

[ClearScriptLib]

That ended up with results in the C# method being null...

To get data back from PutItemAsync, you need to set up a PutItemOperationConfig. For example:

engine.AddHostObject("DynamoClient", client);
engine.AddHostType("DynamoTable", typeof(Table));
engine.AddHostType("DynamoDocument", typeof(Document));
engine.AddHostType("DynamoPutItemOperationConfig", typeof(PutItemOperationConfig));
engine.AddHostType("DynamoReturnValues", typeof(ReturnValues));
engine.Execute(@"
    async function PostDDB() {
        const table = DynamoTable.LoadTable(DynamoClient, 'HelloWorldTable');
        const itemJson = JSON.stringify(data);
        const docItem = DynamoDocument.FromJson(itemJson);
        const putItemConfig = new DynamoPutItemOperationConfig();
        putItemConfig.ReturnValues = DynamoReturnValues.AllOldAttributes; 
        return await table.PutItemAsync(docItem, putItemConfig);
    }
");
var result = await (Task<object>)engine.Invoke("PostDDB") as Document;
Console.WriteLine(result?.ToJsonPretty() ?? "[null]");

Without putItemConfig, the operation returns null. Otherwise, it returns the item that was replaced.

Cheers!