0005 Understanding IAsyncEnumerable<T> for Streaming Data

In C#, IAsyncEnumerable<T> is a powerful feature introduced in C# 8.0 (but usable in C# 7 with the System.Interactive.Async NuGet package). It allows you to work with asynchronous streams of data, which is particularly useful when dealing with large datasets or real-time data.

Why use IAsyncEnumerable<T>?

• Efficient Memory Usage: Instead of loading all data into memory at once, you can process items one at a time as they become available.

• Asynchronous Processing: You can await each item in the stream, making it ideal for I/O-bound operations like database queries or API calls.

Example:

Let’s say you want to fetch and process a large number of records from a database asynchronously.

public async IAsyncEnumerable<string> FetchRecordsAsync()
{
    for (int i = 0; i < 10; i++)
    {
        // Simulate an asynchronous operation (e.g., fetching data from a database)
        await Task.Delay(100); // Simulate delay
        yield return $"Record {i}";
    }
}

public async Task ProcessRecordsAsync()
{
    await foreach (var record in FetchRecordsAsync())
    {
        Console.WriteLine($"Processing: {record}");
    }
}

Key Points:

1. yield return in Async Methods:

   • The yield return statement is used to return items one at a time from the IAsyncEnumerable<T>.

2. await foreach:

   • The await foreach loop is used to asynchronously iterate over the items in the stream.

3. Use Cases:

   • Streaming large datasets from a database.

   • Processing real-time data (e.g., IoT sensor data).

   • Paginated API calls.

Gotchas:

• Cancellation: If you need to cancel the operation, pass a CancellationToken to the async method.

• Error Handling: Handle exceptions within the async stream to avoid breaking the enumeration.

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  Advanced Example: Combining with Entity Framework

  If you’re using Entity Framework, you can use IAsyncEnumerable<T> to stream query results efficiently:

public async IAsyncEnumerable<Customer> GetCustomersAsync()
{
    using (var context = new MyDbContext())
    {
        await foreach (var customer in context.Customers.AsAsyncEnumerable())
        {
            yield return customer;
        }
    }
}

This avoids loading all customers into memory at once, which is especially useful for large datasets.