vb.net 多查询一张表

Question

I'm using VS to build an app that queries an access db. In one of the form tabs there are 12 buttons and near each button a label were it shows the number of pressed times. When the form loads it queries the DB to show the number of times the user pressed in that day.

Public Class Form1
Dim connString As String = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=\\networkdrive\DB_Reg_V01_10.accdb"
Dim da1, da2, da3, da4, da5, da6, da7, da8, da9, da10, da11, da12 As OleDbDataAdapter
Dim ds1, ds2, ds3, ds4, ds5, ds6, ds7, ds8, ds9, ds10, ds11, ds12 As DataSet
Dim tables As DataTableCollection
Dim source1 As New BindingSource
Dim provider, dataFile As String
Dim cmd As OleDbCommand = Nothing
Dim myConnection As OleDbConnection = New OleDbConnection

Private Sub Form1_Load(sender As System.Object, e As EventArgs) Handles MyBase.Load

ds1 = New DataSet
tables = ds1.Tables
da1 = New OleDbDataAdapter("Select Count(*) from TB_Atividades Where ([User] = '" & boxUser.Text & "') AND (Data = DATE()) AND (Prod = 'Cat23')", myConnection)
da1.Fill(ds1, "ID")
Dim view1 As New DataView(tables(0))
DataGridView1.DataSource = view1
lblCount1.Text = DataGridView1.CurrentCell.Value.ToString()

ds2 = New DataSet
tables = ds2.Tables
da2 = New OleDbDataAdapter("Select Count(*) from TB_Atividades Where ([User] = '" & boxUser.Text & "') AND (Data = DATE()) AND (Prod = 'Cat4410')", myConnection)
da2.Fill(ds2, "ID")
Dim view1 As New DataView(tables(0))
DataGridView1.DataSource = view2
lblCount2.Text = DataGridView1.CurrentCell.Value.ToString()

/.../

ds12 = New DataSet
tables = ds12.Tables
da12 = New OleDbDataAdapter("Select Count(*) from TB_Atividades Where ([User] = '" & boxUser.Text & "') AND (Data = DATE()) AND (Prod = 'Cat101')", myConnection)
da12.Fill(ds12, "ID")
Dim view12 As New DataView(tables(0))
DataGridView1.DataSource = view12
lblCount12.Text = DataGridView1.CurrentCell.Value.ToString()

/.../

The code is working but it takes some time to start. I just what to make it more efficient.

It's there a way to reduce the number of call's to the DB?

Thnks in advance.

Answer 1

You need to learn how to do functions and parametrize your query . Your connection need to be open for the shorted amount of time. If you just need the count, you just need to call ExecuteScalar instead of having a whole dataset.

Function GetCount(ByVal user As String, ByVal product As String) As Integer

    Dim result As Integer
    Dim command As New OleDbCommand("Select Count(*) from TB_Atividades Where ([User] = ?) AND (Data = DATE()) AND (Prod = ?)", connection)

    command.Parameters.Add(user)
    command.Parameters.Add(product)

    myConnection.Open()
    result = command.ExecuteScalar()
    myConnection.Close()

    return result
End Function


lblCount1.Text = GetCount(boxUser.Text, "Cat23")
lblCount2.Text = GetCount(boxUser.Text, "Cat4410")

I can't test this so don't just copy/paste it. I hope this will give you guidance to take the correct steps.

If you need to query all categories, then just return a list of all your category and loop through them. A better to query the database the least amount of time.

SELECT Prod, count(*) FROM ... GROUP BY Prod

Answer 2

If you are going to use all your logics in Form_Load event then it will take some time to complete its operation which results in delay of form loading.

In order to avoid that you need to implement Threading concept in your application. You need to create a new thread and write the logics inside it. Start the thread in Form_Load event and display a loading symbol in your form until execution of thread is over.

Instead of querying the database often, you can fetch all the records from the database and store it in a DataTable. use DataTable.select("your query") to filter out the records based on your requirement.