You have 3 options:
- Use the built-in driver method (e.g.
ForEachAsync
,ToListAsync
). - On C# 8.0 and above you can convert the
IAsyncCursor
into anIAsyncEnumerable
and useawait foreach
or any async LINQ operator. - Iterate over the
IAsyncCursor
.
Built-in Driver Methods
The driver has some LINQ-like extension methods for IAsyncCursor
, like AnyAsync
, ToListAsync
, etc. For iteration it has ForEachAsync
:
var cursor = await client.ListDatabasesAsync();
await cursor.ForEachAsync(db => Console.WriteLine(db["name"]));
Converting to IAsyncEnumerable
On C# 8.0 and above it’s much nicer to iterate with await foreach
(and use async LINQ). This requires wrapping the IAsyncCursor
in an IAsyncEnumerable
.
You can do it yourself but since its important to get some critical things right (like cancellation and disposal) I’ve published a nuget package: MongoAsyncEnumerableAdapter
var cursor = await client.ListDatabasesAsync();
await foreach (var db in cursor.ToAsyncEnumerable())
{
Console.WriteLine(db["name"]);
}
Custom iteration
Traditional iteration in C# is done with IEnumerable
and foreach
. foreach
is the compiler’s syntactic sugar. It’s actually a call to GetEnumerator
, a using
scope and a while
loop:
using (var enumerator = enumerable.GetEnumerator())
{
while (enumerator.MoveNext())
{
var current = enumerator.Current;
// use current.
}
}
IAsyncCursor
is equivalent to IEnumerator
(the result of IEnumerable.GetEnumerator
) while IAsyncCursorSource
is to IEnumerable
. The difference is that these support async
(and get a batch each iteration and not just a single item). So you can implement the whole using
, while
loop thing yourself:
IAsyncCursorSource<int> cursorSource = null;
using (var asyncCursor = await cursorSource.ToCursorAsync())
{
while (await asyncCursor.MoveNextAsync())
{
foreach (var current in asyncCursor.Current)
{
// use current
}
}
}