Mongodb驱动程序2.0在VB.net中查找（）不起作用

Question

我正在尝试使用MongoDB的C＃驱动程序2.0进行练习。我不知道C＃，所以我在Visual Basic中编写代码。

当我尝试打印出列表代码不会编译。我知道我已将For Each内容注释掉了，但这不是问题。我想查询集合中所有文档的数据库，并将它们打印到文本框中。

下面是不工作的代码。最后一部分给了我麻烦。

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 

任何帮助表示赞赏。几个小时以来，我一直在敲击键盘。

以下是为我工作后ALEX给我一个答案的代码：

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 

我不得不异步添加到子。我也有我的关键“名称”不正确。之后，事情进展顺利。呜呼！

Answer 1

您的问题是在这条线：

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

到ToListAsync()方法的调用返回awaitable Task(Of List(Of BsonDocument))，即一个承诺，它将返回时，它已经完成它获取可以列举的清单。您需要Await它才能进入列表。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的驱动器提供了一个替代的构建体，是利用其ForEachAsync方法，并用的λ代表一个参数提供它。