說起來，查看Mongodb官方的接口文檔是場噩夢，盡管mongodb官方花了大力氣整頓了它的API，但是簡單的接口羅列，0代碼示范，讓人無從開始。幸虧有很多天才，成功破譯，我才得以沿著他們走的路，照貓畫虎的走下去。整個項目結構如下：
類文件中vbtest.vb數據庫實體類對應著mongodb文檔vbtest，用于數據操作測試
Imports MongoDB.Bson
Public Class vbtest
Public _id As ObjectId
Public content As String
End Class
（optional）vbmongo.vb是綁定好數據庫實體類vbtest的版本
Imports MongoDB.Bson
Imports MongoDB.Driver
Public Class vbmongo
Public client
Public collection As IMongoCollection(Of vbtest)
Public database As IMongoDatabase
Public mlist As List(Of vbtest)
Public builder As FilterDefinitionBuilder(Of vbtest) = New FilterDefinitionBuilder(Of vbtest)
Public filter As FilterDefinition(Of vbtest)
Public Sub New(ByVal dbname As String, ByVal collectionname As String)
client = New MongoClient("mongodb://127.0.0.1:27017")
database = client.GetDatabase(dbname)
collection = database.GetCollection(Of vbtest)(collectionname)
End Sub
Public Async Function loadrecords() As Task(Of List(Of vbtest))
filter = builder.Ne(Of ObjectId)("_id", New ObjectId())//_id不等于空的記錄，通過這種方法蹩腳的實現了查找全部的功能Builder的大多數條件設置函數都用到了泛型Ne（Of TField）
Dim mlist As List(Of vbtest) = Await collection.Find(filter).ToListAsync()//TField可以理解為 type of field 對應的是實體類中字段的數據類型例如 OBjectId或者String等等
Return mlist
End Function
Public Async Function loadone(ByVal _id As String) As Task(Of vbtest)
filter = builder.Eq(Of ObjectId)("_id", New ObjectId(_id))
Dim mlist As vbtest = Await collection.Find(filter).FirstOrDefaultAsync()
Return mlist
End Function
Public Async Function updateone(ByVal _id As String, ByVal doc As vbtest) As Task(Of vbtest)
filter = builder.Eq(Of ObjectId)("_id", New ObjectId(_id))
Dim up As UpdateDefinitionBuilder(Of vbtest) = New UpdateDefinitionBuilder(Of vbtest)()
Dim updef As UpdateDefinition(Of vbtest)
updef = up.Set(Of String)("content", doc.content)
'.Set(Of String)("content", doc)
collection.UpdateOneAsync(filter, updef)
End Function
End Class
說起來mongodb的連接可以分幾步，根據連接字符串打開鏈接，獲取數據庫，獲取文檔，進而在文檔的基礎上進行增刪改查。對于vb.net操作mongodb，完全是根據c#的操作范例，根據vb.net的語法特點臨摹出來的。
首先需要對項目進行Nuget包的安裝，我們要搜尋的是MongoDB.Driver
這里創建了一個vb.net的泛型類vbmongoT，只寫了單個查找，查找列表和更新操作，函數中大量成對出現了Async和Await關鍵字，用于標識該功能使用了異步編程,在窗體程序中進行調用的時候，仍需要在成對的使用Async Await的關鍵字，因為異步函數返回的往往是TaskTResult>類型（c#）或者 Task（Of TResult） （vb.net）需要在調用函數體中使用await關鍵字拿到最終結果Imports MongoDB.BsonImports MongoDB.Driver
Public Class vbmongoT(Of T)
Public client
Public collection As IMongoCollection(Of T)
Public database As IMongoDatabase
Public mlist As List(Of T)
Public builder As FilterDefinitionBuilder(Of T) = New FilterDefinitionBuilder(Of T)
Public up As UpdateDefinitionBuilder(Of T)
Public updef As UpdateDefinition(Of T)
Public filter As FilterDefinition(Of T)
Public Sub New(ByVal dbname As String, ByVal collectionname As String)
client = New MongoClient("mongodb://127.0.0.1:27017")
database = client.GetDatabase(dbname)
collection = database.GetCollection(Of T)(collectionname)
End Sub
Public Async Function loadrecords() As Task(Of List(Of T))
filter = builder.Ne(Of ObjectId)("_id", New ObjectId())
Dim mlist As List(Of T) = Await collection.Find(filter).ToListAsync()
Return mlist
End Function
Public Async Function loadone(ByVal _id As String) As Task(Of T)
filter = builder.Eq(Of ObjectId)("_id", New ObjectId(_id))//_id滿足查找條件的記錄，Builder的大多數條件設置函數都用到了泛型：例如Ne（Of TField）
Dim mlist As T = Await collection.Find(filter).FirstOrDefaultAsync()
Return mlist
End Function
Public Async Function updateone(ByVal filter As FilterDefinition(Of T), ByVal updef As UpdateDefinition(Of T)) As Task(Of T)
'updef = up.Set(Of String)("content", doc.content) '.Set(Of String)("content", doc)
Await collection.UpdateOneAsync(filter, updef)
End Function
End Class
在mongodb這一版本的官方API里，IMongoCollection對象是查找，添加，更新，刪除等動作的發起者，這里面查找，更新，刪除都要用到查詢條件，
官方謂之filter（過濾器）C#: FilterDefinitionT> VB.net:FilterDefinition (Of T)
而過濾器是過濾器模具的建模結果
過濾器模具：C#: FilterDefinitionBuilderT> VB.net:FilterDefinitionBuilder (Of T)
在Mongodb.Driver這個大類下面 建議直接翻看FilterDefinitionBuilder的介紹 https://mongodb.github.io/mongo-csharp-driver/2.10/apidocs/html/T_MongoDB_Driver_FilterDefinitionBuilder_1.htm
同樣的數據庫文檔的更新操作由UpdateDefinitionBuilder 設置更新字段后產生的 UpdateDefinition完成
窗體程序部分
Imports MongoDB.Bson
Imports MongoDB.Driver
Public Class Form1
Public client
Public bsdoc As vbtest
Public collection As IMongoCollection(Of vbtest)
Public database As IMongoDatabase
Public mlist As List(Of vbtest)
Public builder As FilterDefinitionBuilder(Of vbtest) = New FilterDefinitionBuilder(Of vbtest)
Public vm As vbmongoT(Of vbtest) = New vbmongoT(Of vbtest)("meandmycoach", "vbtest")
Public filter As FilterDefinition(Of vbtest)
Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
bsdoc.content = RichTextBox1.Text
vm.filter = vm.builder.Eq(Of ObjectId)("_id", New ObjectId(ComboBox1.Text))
vm.up = New UpdateDefinitionBuilder(Of vbtest)
vm.updef = vm.up.Set(Of String)("content", bsdoc.content)
'vm.up.Set(Of String)("content", bsdoc.content)
vm.updef = vm.up.Combine(vm.updef)
vm.updateone(vm.filter, vm.updef)
End Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
vm = New vbmongoT(Of vbtest)("meandmycoach", "vbtest")
Dim bsdoc As vbtest = New vbtest()
End Sub
Private Async Sub PictureBox1_Click(sender As Object, e As EventArgs) Handles PictureBox1.Click
mlist = Await vm.loadrecords()
For i As Integer = 0 To mlist.Count - 1
ComboBox1.Items.Add(mlist(i)._id.ToString())
Next
ComboBox1.Text = ComboBox1.Items(0)
Label2.Text = mlist.Count.ToString()
End Sub
Private Sub RichTextBox1_TextChanged(sender As Object, e As EventArgs) Handles RichTextBox1.TextChanged
End Sub
Private Async Sub ComboBox1_TextChanged(sender As Object, e As EventArgs) Handles ComboBox1.TextChanged
bsdoc = Await vm.loadone(ComboBox1.Text)
RichTextBox1.Text = bsdoc.content
End Sub
Private Async Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
End Sub
End Class
功能描述：通過點擊圖片，加載所有的vbtest文檔記錄，combobox1專門用于顯示ObjectId，可以通過ToString()方法轉換為普通字符串
隨著下拉框ObjectId的改變，richtext1控件加載vbtest實體類對應記錄的Content字段，可以更改字段內容后點擊更新提交按鈕完成文檔的UpdateOneAsync操作
總結
到此這篇關于vs2019 下用 vb.net編寫窗體程序連接 mongodb4.2的文章就介紹到這了,更多相關vs2019連接 mongodb4.2內容請搜索腳本之家以前的文章或繼續瀏覽下面的相關文章希望大家以后多多支持腳本之家！
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