blocks|key|3279685|text|简短回答：使用ForEachAsync扩展方法：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|3279686|var+cursor+=+await+client.ListDatabasesAsync();
await+cursor.ForEachAsync(db+=>+Console.WriteLine(db["name"]));|code-block|syntax|javascript|3279687|长答案：在C#中的传统迭代是使用IEnumerable和foreach完成的。foreach是编译器的语法糖。它实际上是一个对GetEnumerator的调用，一个using作用域和一个while循环。但这不支持异步操作：|3279688|using+(var+enumerator+=+enumerable.GetEnumerator())
{
++++while+(enumerator.MoveNext())
++++{
++++++++var+current+=+enumerator.Current;
++++++++//+use+current.
++++}
}|3279689|IAsyncCursor等同于IEnumerator+(IEnumerable.GetEnumerator的结果)，而IAsyncCursorSource等同于IEnumerable。不同之处在于，它们支持async+(并在每次迭代中获得批处理，而不仅仅是单个项)。你不能使用foreach，因为它是为IEnumerable构建的，但是你可以实现整个using，while循环：|3279690|IAsyncCursorSource<int>+cursorSource+=+null;

using+(var+asyncCursor+=+await+cursorSource.ToCursorAsync())
{
++++while+(await+asyncCursor.MoveNextAsync())
++++{
++++++++foreach+(var+current+in+asyncCursor.Current)
++++++++{
++++++++++++//+use+current
++++++++}
++++}
}|3279691|然而，这是大量的样板文件，因此驱动程序为IAsyncCursor添加了ForEachAsync、ToListAsync等扩展方法。|3279692|这涵盖了大多数常见用例，但对于其他用例，您仍然需要自己实现迭代。|3279693|entityMap^0|0|5|7|C|0|0|0|4|G|B|S|7|13|7|1R|D|2A|5|2L|5|0|0|0|C|F|B|S|P|1N|I|28|B|2V|5|3U|7|47|B|4V|5|51|5|0|0|K|C|Z|C|1C|B|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|D]]|E|@]|F|$]]|$1|G|3|H|5|I|7|14|8|@]|E|@]|F|$J|K]]|$1|L|3|M|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|D]|$9|1A|A|1B|B|D]|$9|1C|A|1D|B|D]|$9|1E|A|1F|B|D]|$9|1G|A|1H|B|D]|$9|1I|A|1J|B|D]]|E|@]|F|$]]|$1|N|3|O|5|I|7|1K|8|@]|E|@]|F|$J|K]]|$1|P|3|Q|5|6|7|1L|8|@$9|1M|A|1N|B|D]|$9|1O|A|1P|B|D]|$9|1Q|A|1R|B|D]|$9|1S|A|1T|B|D]|$9|1U|A|1V|B|D]|$9|1W|A|1X|B|D]|$9|1Y|A|1Z|B|D]|$9|20|A|21|B|D]|$9|22|A|23|B|D]|$9|24|A|25|B|D]]|E|@]|F|$]]|$1|R|3|S|5|I|7|26|8|@]|E|@]|F|$J|K]]|$1|T|3|U|5|6|7|27|8|@$9|28|A|29|B|D]|$9|2A|A|2B|B|D]|$9|2C|A|2D|B|D]]|E|@]|F|$]]|$1|V|3|W|5|6|7|2E|8|@]|E|@]|F|$]]|$1|X|3|-4|5|6|7|2F|8|@]|E|@]|F|$]]]|Y|$]]

Short answer: use the <code>ForEachAsync</code> extension method:

<pre><code>var cursor = await client.ListDatabasesAsync();
await cursor.ForEachAsync(db =&gt; Console.WriteLine(db["name"]));
</code></pre>

Long answer: Traditional iteration in C# is done with <code>IEnumerable</code> and <code>foreach</code>. <code>foreach</code> is the compiler's syntactic sugar. It's actually a call to <code>GetEnumerator</code>, a <code>using</code> scope and a <code>while</code> loop. But that doesn't support asynchronous operations:

<pre><code>using (var enumerator = enumerable.GetEnumerator())
{
 while (enumerator.MoveNext())
 {
 var current = enumerator.Current;
 // use current.
 }
}
</code></pre>

<code>IAsyncCursor</code> is equivalent to <code>IEnumerator</code> (the result of <code>IEnumerable.GetEnumerator</code>) while <code>IAsyncCursorSource</code> is to<code>IEnumerable</code>. The difference is that these support <code>async</code> (and get a batch each iteration and not just a single item). You can't use <code>foreach</code> as it's built for <code>IEnumerable</code> but you can implement the whole <code>using</code>, <code>while</code> loop thing:

<pre><code>IAsyncCursorSource&lt;int&gt; cursorSource = null;

using (var asyncCursor = await cursorSource.ToCursorAsync())
{
 while (await asyncCursor.MoveNextAsync())
 {
 foreach (var current in asyncCursor.Current)
 {
 // use current
 }
 }
}
</code></pre>

However that's a lot of boilerplate so the driver adds extension methods for <code>IAsyncCursor</code> like <code>ForEachAsync</code>, <code>ToListAsync</code> and so forth. 

That covers most common use cases but for others you do still need to implement the iteration yourself.

blocks|key|5597787|text|我个人喜欢将光标转换为C#+8+IAsyncEnumerable，这样您就可以获得使用可枚举项(主要是LINQ)的所有好处。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5597788|使用@i3arnon的"long+answer“我创建了这个扩展方法：|5597789|public+static+async+IAsyncEnumerable<T>+ToAsyncEnumerable<T>(this+IAsyncCursor<T>+asyncCursor)
{
++++while+(await+asyncCursor.MoveNextAsync())
++++{
++++++++foreach+(var+current+in+asyncCursor.Current)
++++++++{
++++++++++++yield+return+current;
++++++++}
++++}
}|code-block|syntax|javascript|5597790|entityMap^0|G|G|1F|4|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

I personally like to convert the cursor into a C# 8 <code>IAsyncEnumerable</code>, that way you get all the benefits of working with enumerables (<code>LINQ</code> mainly).
Using @i3arnon's &quot;long answer&quot; I created this extension method:
<pre><code>public static async IAsyncEnumerable&lt;T&gt; ToAsyncEnumerable&lt;T&gt;(this IAsyncCursor&lt;T&gt; asyncCursor)
{
 while (await asyncCursor.MoveNextAsync())
 {
 foreach (var current in asyncCursor.Current)
 {
 yield return current;
 }
 }
}
</code></pre>

blocks|key|5597796|text|多亏了C#+9中对GetAsyncEnumerator的扩展方法的支持和foreach的鸭式实现，现在可以使用以下扩展方法直接迭代游标：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5597797|public+static+class+MongoDbCursorExtensions
{
++++public+static+IAsyncCursor<T>+GetAsyncEnumerator<T>(this+IAsyncCursor<T>+cursor)+=>+cursor;
}|code-block|syntax|javascript|5597798|用法：|5597799|var+cursor+=+await+collection.Find(filter).ToCursorAsync();
await+foreach+(var+batch+in+cursor)+//+extension+method+implicitly+called+here
{
++++foreach+(var+item+in+batch)
++++{
++++++++//+...
++++}
}|5597800|请参阅：https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/statements/iteration-statements#the-foreach-statement|5597801|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/statements/iteration-statements#the-foreach-statement^0|9|I|10|7|0|0|0|0|4|3B|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|14|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|16|8|@]|D|@$9|17|A|18|1|19]]|E|$]]|$1|Q|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]]]

Thanks to the support of extension methods for <code>GetAsyncEnumerator</code> in C# 9 and the duck-typed implementation of <code>foreach</code> it is now possible to iterate the cursor directly using the following extension method:
<pre><code>public static class MongoDbCursorExtensions
{
 public static IAsyncCursor&lt;T&gt; GetAsyncEnumerator&lt;T&gt;(this IAsyncCursor&lt;T&gt; cursor) =&gt; cursor;
}
</code></pre>
Usage:
<pre><code>var cursor = await collection.Find(filter).ToCursorAsync();
await foreach (var batch in cursor) // extension method implicitly called here
{
 foreach (var item in batch)
 {
 // ...
 }
}
</code></pre>
See: <a href="https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/statements/iteration-statements#the-foreach-statement" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/statements/iteration-statements#the-foreach-statement</a>

I'm trying to get a list of all the databases in my server and ultimately print them out (i.e. use their names as <code>string</code>s). With the previous version of the c# driver I could call the <code>Server.GetDatabases()</code>, but that has been replaced with <code>ListDatabasesAsync()</code>.

The return value is an <code>IAsyncCursor&lt;&gt;</code> and I'm not sure what to do with it. How does one iterate through the list of databases (or anything) with such a cursor?

How is an IAsyncCursor used for iteration with the mongodb c# driver?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在尝试获取我的服务器中所有数据库的列表，并最终将它们打印出来(即使用它们的名称作为string)。使用以前版本的c#驱动程序，我可以调用Server.GetDatabases()，但它已被ListDatabasesAsync()所取代。返回值是一个IAsyncCursor<>，我不知道如何处理它。如何使用这样的游标...

问如何将IAsyncCursor用于mongodb c#驱动程序的迭代？
EN

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问如何将IAsyncCursor用于mongodb c#驱动程序的迭代？EN