Using imperative binding for adding documents in Cosmos DB

Question

I'm using Azure Functions and want to use an imperative binding to my Cosmos DB repository.

At first I had defined my output parameter like this in the Run-method:

[DocumentDB("TablesDB", "minified-urls", ConnectionStringSetting = "CosmosConnectionString", CreateIfNotExists = true)] out MinifiedUrl minifiedUrl,

this works great.

But I'd rather use imperative binding, so I can define the values used in the binding dynamically.

First thing I tried was this, which doesn't work, because you need to set the ConnectionStringSetting.

var output = await binder.BindAsync<MinifiedUrl>(new DocumentDBAttribute("TablesDB", "minified-urls"));

So changing this piece of binding to the following should work, at least that's what I thought.

var output = await binder.BindAsync<MinifiedUrl>(new DocumentDBAttribute("TablesDB", "minified-urls")
{
    CreateIfNotExists = true,
    ConnectionStringSetting = "CosmosConnectionString"
});

When you do this, the binder is complaining about a missing Id property and if you fill this Id property you also need to set the PartitionKey.

So in the end this is what I came up with.

var output = await binder.BindAsync<MinifiedUrl>(new DocumentDBAttribute("TablesDB", "minified-urls")
{
    CreateIfNotExists = true,
    ConnectionStringSetting = "CosmosConnectionString",
    Id = Guid.NewGuid().ToString(),
    PartitionKey = DateTime.UtcNow.Year.ToString()
});

Because I want to create a new document inside the repository, the binder is not able to find something, therefore the output variable is null.

So, what I'd like to know is how to proceed? The declarative binding works properly, but I can't figure out how to get this imperative working.

Mikhail Shilkov Mikhail Shilkov · Accepted Answer · 2017-10-18T20:23:27

Your problems come from the fact that runtime interprets your imperative binding as input one. That's because you are requesting the custom type (MinifiedUrl), so it makes sense that this value should be loaded from the database.

To make your binding output, you should request IAsyncCollector type, and then call AddAsync on it:

var output = await binder.BindAsync<IAsyncCollector<MinifiedUrl>>(
    new DocumentDBAttribute("TablesDB", "minified-urls")
    { 
        CreateIfNotExists = true,
        ConnectionStringSetting = "CosmosConnectionString"
    });
await output.AddAsync(new MinifiedUrl(...));

Using imperative binding for adding documents in Cosmos DB

2 Answers