Mongodb驅動程序2.0在VB.net中查找（）不起作用

Question

我正在嘗試使用MongoDB的C＃驅動程序2.0進行練習。我不知道C＃，所以我在Visual Basic中編寫代碼。

當我嘗試打印出列表代碼不會編譯。我知道我已將For Each內容註釋掉了，但這不是問題。我想查詢集合中所有文檔的數據庫，並將它們打印到文本框中。

下面是不工作的代碼。最後一部分給了我麻煩。

Private Sub btnListUsers_Click(sender As Object, e As EventArgs) Handles btnListUsers.Click 

    Dim ConnString As String 
    ConnString = txtConnStr.Text 

    Dim vDbName As String 
    vDbName = txtDb.Text 

    Dim vColName As String 
    vColName = txtColl.Text 

    Dim vClient As MongoClient 

    vClient = DbConnection(ConnString, vDbName, vColName) 

    Dim vDb As MongoDatabaseBase 
    vDb = vClient.GetDatabase(vDbName) 

    Dim vCol As IMongoCollection(Of BsonDocument) 
    vCol = vDb.GetCollection(Of BsonDocument)(vColName) 

    Dim query As BsonDocument 
    query = New BsonDocument("Names", txtListUsers.Text) 

    For Each item As BsonDocument In vCol.Find(query).ToListAsync() 
     'print a count 
     'print bson document 

    Next 

End Sub 

任何幫助表示讚賞。幾個小時以來，我一直在敲擊鍵盤。

以下是爲我工作後ALEX給我一個答案的代碼：

Private Async Sub btnListUsers_Click(sender As Object, e As EventArgs) Handles btnListUsers.Click 

     Dim ConnString As String 
     ConnString = txtConnStr.Text 

     Dim vDbName As String 
     vDbName = txtDb.Text 

     Dim vColName As String 
     vColName = txtColl.Text 

     Dim vClient As MongoClient 

     vClient = DbConnection(ConnString, vDbName, vColName) 

     Dim vDb As MongoDatabaseBase 
     vDb = vClient.GetDatabase(vDbName) 

     Dim vCol As IMongoCollection(Of BsonDocument) 
     vCol = vDb.GetCollection(Of BsonDocument)(vColName) 

     Dim query As BsonDocument 
     query = New BsonDocument("Name", txtListUsers.Text) 

     Dim myList As List(Of BsonDocument) = Await vCol.Find(query).ToListAsync() 

     Dim i As Integer = 0 

     For Each vItem As BsonDocument In myList 

      'count 
      i += 1 

      'print bson document 
      rtfDataDisplay.Text = rtfDataDisplay.Text & vbCrLf & "#" & i.ToString & " - " & vItem.ToString & vbCrLf 

     Next 

    End Sub 

我不得不異步添加到子。我也有我的關鍵「名稱」不正確。之後，事情進展順利。嗚呼！

Answer 1

您的問題是在這條線：

For Each item As BsonDocument In vCol.Find(query).ToListAsync() 

到ToListAsync()方法的調用返回awaitable Task(Of List(Of BsonDocument))，即一個承諾，它將返回時，它已經完成它獲取可以列舉的清單。您需要Await它才能進入列表。如：

Dim myList As List(Of BsonDocument) = Await vCol.Find(query).ToListAsync() 
For Each item As BsonDocument in myList 
    'print a count 
    'print bson document 
Next  

由MongoDB的驅動器提供了一個替代的構建體，是利用其ForEachAsync方法，並用的λ代表一個參數提供它。