How can I use LINQ in CosmosDB SDK v3.0 async query?

Question

I\'ve been following the official documentation here: https://docs.microsoft.com/en-us/azure/cosmos-db/sql-api-get-started#Query

But I can\'t figure out how to correctly

Answer 1

If your application follows a layered architecture and you'd like to give your domain layer full control over the query then it's possible to wrap cosmos IQueryable with a custom IQueryProvider that implements IAsyncEnumerable e.g.

By doing that you can hide the implementation details of asynchronously iterating over the result from your domain layer.

Persistence layer

public class PersonRepository
{
    public IQueryable Persons => _cosmosContainer.GetItemLinqQueryable().ToCosmosAsyncQueryable();
}

Domain layer

var persons = await _personRepository.Persons
    .Where(p => p.Name == "Name")
    .AsAsyncQueryable()
    .ToListAsync(cancellationToken);

• ToListAsync is available from System.Linq.Async that can be referenced from your domain layer

Domain layer extensions

public static IAsyncEnumerable AsAsyncQueryable(this IQueryable queryable)
{
    return (IAsyncEnumerable)queryable;
}

Persistence layer extensions

internal static class CosmosAsyncQueryableExtensions
{
    internal static IQueryable ToCosmosAsyncQueryable(this IOrderedQueryable source)
    {
        return new CosmosAsyncQueryable(source);
    }
}

internal class CosmosAsyncQueryable : IEnumerable, IQueryable, IAsyncEnumerable
{
    private readonly IQueryable _queryable;

    public CosmosAsyncQueryable(IQueryable queryable)
    {
        _queryable = queryable;
        Provider = new CosmosAsyncQueryableProvider(queryable.Provider);
    }

    public Type ElementType => typeof(TResult);

    public Expression Expression => _queryable.Expression;

    public IQueryProvider Provider { get; }

    public IEnumerator GetEnumerator() => _queryable.GetEnumerator();

    IEnumerator IEnumerable.GetEnumerator() => _queryable.GetEnumerator();

    public async IAsyncEnumerator GetAsyncEnumerator(CancellationToken cancellationToken = default)
    {
        var iterator = _queryable.ToFeedIterator();

        while (iterator.HasMoreResults)
        {
            foreach (var item in await iterator.ReadNextAsync(cancellationToken))
            {
                yield return item;
            }
        }
    }
}

internal class CosmosAsyncQueryableProvider : IQueryProvider
{
    private readonly IQueryProvider _provider;

    public CosmosAsyncQueryableProvider(IQueryProvider provider) => _provider = provider;

    public IQueryable CreateQuery(Expression expression) =>
        new CosmosAsyncQueryable(_provider.CreateQuery(expression));

    public IQueryable CreateQuery(Expression expression) => CreateQuery