I have a form with one combo box and text box, and an SQL database
named balance with two columns; one as customername and the other as obbalance.
I had bound all of the customer name to the combo box, now what I have to do is,
when a user selects a customer name from the combo box, the text box should show the obbalance of the selected customername; here, the customer name will not be repeated - only one name per customer.
What can I do? Please help me.
Dim conectionstring As String
conectionstring = "Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Documents and Settings\Administrator\My Documents\Visual Studio 2005\Projects\SHOPPROJECT\SHOPPROJECT\shop.mdf;Integrated Security=True;User Instance=True"
Dim ST As String = ComboBox1.SelectedText
Dim sqlcon As New SqlConnection(conectionstring)
Dim sqlcmd As New SqlCommand("SELECT OBBALANCE FROM BALANCE WHERE CUSTOMERNAME = " & " '" & ST & "'" & "", sqlcon)
MessageBox.Show(TextBox1.Text)
Dim result As Object
Try
sqlcon.Open()
' Dim sdr As SqlDataReader = sqlcmd.ExecuteReader()
result = sqlcmd.ExecuteScalar()
If result IsNot Nothing Then
TextBox1.Text = result.ToString()
MessageBox.Show(TextBox1.Text)
End If
Catch ex As SqlException
MessageBox.Show(ex.Message)
End Try
End Sub
I've tried this, but I can't see the value in the text box, and obbalance is a floating-point value from the SQL database.
If you're updating a text box, is this a single result (scalar value)? If so, the first thing I'd do is use ExecuteScalar not ExecuteReader. Then, use debug mode with breakpoints to get a better idea of what is actually happening. It may simply be that you're not getting any results.
Note: I'm assuming the bad coding practice (in-line sql statement, hard-coded connection string, etc.) are for clarity. If they're not, fix them.
Make the follwing changes:
Dim sqlcmd As New SqlCommand("SELECT OBBALANCE FROM BALANCE WHERE CUSTOMERNAME = '" & ST & "'", sqlcon)
TextBox1.Text = sdr.GetString(yourColumnIndex)
ComboBox1.SelectedText returns the highlighted (selected) text on the ComboBoxControl. That will be empty if you haven't use your mouse to select a portion of its text or hold the shift while you are pressing the direction keys on your keyboard. And that's probably why your query returns ZERO RECORDS.
Use the following instead:
Dim ST As String = ComboBox1.SelectedItem.Text
Set a breakpoint and ensure you are getting the value for OBBALANCE (see if you are getting any rows period might be good). Also, make sure you can only get one row, as you are iterating forward, even when you only need one value.
Better yet, consider ExecuteScalar, which only returns a single value. While you are at it, parameterize the SQL query so you don't get SQL injected.
UPDATE: Just change it here:
sdr = sqlcmd.ExecuteReader()
to something like
Dim s as String = sqlcmd.ExecuteScalar()
Then use s as your textbox value. You may have to ToString() the value or otherwise cast as string, as I believe the ExecuteScalar() returns an object.
Related
I am creating an attendance management system in vb.net and using MS access as my database. I created a leave form in which the student on leave has a roll number and his details along with the from date and to date field.
What I'm trying to do is to show all the roll numbers of students in the ComboBox on leave if the DateTimePicker value is in between the to date and from date, the command that I created as MS access query is selecting the from date and to date ie., extreme dates matching with the DateTimePicker value but not showing the values if date is between the to and from date.
this is the code and query:
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
con.Open()
Dim cmd1 As New OleDbCommand("Select roll_no From leaves Where semester= " + ComboBox3.SelectedItem + " and (from_date<= #" & DateTimePicker1.Value.ToShortDateString & "# and to_date >= #" & DateTimePicker1.Value.ToShortDateString & "#)", con)
Dim da1 As New OleDbDataAdapter
da1.SelectCommand = cmd1
Dim dt1 As New DataTable
dt1.Clear()
da1.Fill(dt1)
ComboBox4.DataSource = dt1
ComboBox4.DisplayMember = "roll_no"
ComboBox4.ValueMember = "roll_no"
con.Close()
End Sub
Is there any modification in query through which I can get my desired results to get all the roll no if DateTimePicker value is between dates in database?
Well, you probably do want to wrap the code in a using block - that way if you have a error, it will STILL close the connection. Also, it means you don't have to close the connection - a using block ALWAYS will (so, this costs you ONLY one extra line of code, but it more robust - will not leave stray connections open.
Next up:
While everyone warns and suggests to try and avoid string concertation for reasons of SQL injection?
Actually, the BETTER case is that string concatenation is tricky, messy, and you have to remember to use quotes to surround strings, maybe "#" for dates, and for numbers no surrounding delimiters. And one tiny missing single quote or whatever, and your sql is now wrong. So, this is a BETTER case and reason to use parameters - to allow you to write code, and write code that is easer to fix, read, maintain, and even add more parameters to without complex string concatenations.
So, I would suggest this:
Using conn As New OleDbConnection(My.Settings.AccessDB)
Dim strSQL As String =
"Select roll_no From leaves Where from_date >= #cboDate and to_date <= #cboDate " &
"AND semester = #Semester"
Using cmd = New OleDbCommand(strSQL, conn)
cmd.Parameters.Add("#cboDate", OleDbType.DBDate).Value = DateTimePicker1.Value
cmd.Parameters.Add("#Semester", OleDbType.Integer).Value = ComboBox3.SelectedValue
conn.Open()
ComboBox4.DisplayMember = "roll_no"
ComboBox4.ValueMember = "roll_no"
ComboBox4.DataSource = cmd.ExecuteReader
End Using
End Using
And note how I dumped the need for a data adaptor - don't' need it.
And note how I dumped the need for a data table - don't' need it.
However, you do OH SO VERY often need a data table. So, since we humans do things over and over without thinking - memory muscle - then I would suggest that it is ok to create and fill a data table and shove that into the "on leave".
So since we "often" will need a data table, then for the sake of learning, then you could write it this way (so we now learn how to fill a data table).
Using conn As New OleDbConnection(My.Settings.AccessDB)
Dim strSQL As String =
"Select roll_no From leaves Where from_date >= #cboDate and to_date <= #cboDate " &
"AND semester = #Semester"
Using cmd = New OleDbCommand(strSQL, conn)
cmd.Parameters.Add("#cboDate", OleDbType.DBDate).Value = DateTimePicker1.Value
cmd.Parameters.Add("#Semester", OleDbType.Integer).Value = ComboBox3.SelectedValue
conn.Open()
Dim dt1 As New DataTable
dt1.Load(cmd.ExecuteReader)
ComboBox4.DisplayMember = "roll_no"
ComboBox4.ValueMember = "roll_no"
ComboBox4.DataSource = dt1
End Using
End Using
But, either way? Note how I did not have to remember, think about, worry about, and try to figure out the delimiters. Is that a " # " we need for dates, or is that a " ' " we need around the date?
Of course this code would be placed in the timepicker value changed event.
I'm a beginner. I created a database in vb.net and I need to build a query, in the SQL Statement - Table Adapter, which returns records even if parameters are NULL in one or more textbox. To be clear, I have several textboxes (related to fields) with which I can filter record results and I want to refine my research as much as I fill textboxes, reverse if I fill just one of them randomly.
Sorry if I confused you, but I guess you get it anyway.
In its simplest form (assuming SQL server param concepts)
-- Define your columns to pull back/display
select t1.column1, t1.column2, t1.column3...
-- Define the table, give it an alias if you're using more than one or it has a silly name
from thetable t1
-- Apply filters
where
-- For each textbox/column search combo, do this...
(column1 = #field1 or #field1 is null)
or -- If the filter is restrictive, use AND here
(column2 = #field2 or #field2 is null)
or -- If the filter is restrictive, use AND here
...
I would dump the table adapter for this requirement.
I am building the sql string using a StringBuilder. StringBuilder objects are mutable, String is not.
To run this Code
1. I assumed Sql Server. If this is not the case change all the data object (Connectio and Command) to the proper provider.
Add your connection string to the constructor of the connection.
Add your table name where it says "YourTable"
I just used TextBox1 etc. as control names. Use your actual control names
Replace Field1, Field2 etc. with your actual column names.
The parameter names (by convention, they start with #) can be anything you want as long as they match the name you add to the Parameters collection.
You will have to check your database for the actual datatypes of the fields. Be sure to convert the TextBox values to the compatible type. TextBox.Text is a string so it will be compatible to .VarChar but note number types or dates.
I added a Debug.Print to check what the Sql string looks like. Be cautious about where I have spaces when building the string. You can see the result in the immediate window (available from Debug menu).
If you don't already have a DataGridView on your form, add one so you can see the reults of your query.
Finally, always use parameters, use Using...End Using blocks, and open your connection at the last minute.
Private Sub RunDynamicQuery()
Dim sb As New StringBuilder
Dim AndNeeded As Boolean
Dim dt As New DataTable
Using cn As New SqlConnection("Your connection string")
Using cmd As New SqlCommand
sb.Append("Select * From YourTable Where ")
If Not String.IsNullOrEmpty(TextBox1.Text) OrElse Not String.IsNullOrWhiteSpace(TextBox1.Text) Then
sb.Append("Field1 = #Field1")
cmd.Parameters.Add("#Field1", SqlDbType.Int).Value = CInt(TextBox1.Text)
AndNeeded = True
End If
If Not String.IsNullOrEmpty(TextBox2.Text) OrElse Not String.IsNullOrWhiteSpace(TextBox2.Text) Then
If AndNeeded Then
sb.Append(" And")
End If
sb.Append(" Field2 = #Field2")
cmd.Parameters.Add("#Field2", SqlDbType.VarChar).Value = TextBox2.Text
AndNeeded = True
End If
If Not String.IsNullOrEmpty(TextBox3.Text) OrElse Not String.IsNullOrWhiteSpace(TextBox3.Text) Then
If AndNeeded Then
sb.Append(" And")
End If
sb.Append(" Field3 = #Field3")
cmd.Parameters.Add("#Field3", SqlDbType.VarChar).Value = TextBox3.Text
AndNeeded = True
End If
sb.Append(";")
cmd.Connection = cn
Debug.Print(sb.ToString)
cmd.CommandText = sb.ToString
cn.Open()
dt.Load(cmd.ExecuteReader)
End Using
End Using
DataGridView1.DataSource = dt
End Sub
I have an inventory in Visual basic that get the product name and the unit name in the database which is Microsoft Access. Everything is fine except when I retrieve a string with a character dot(.). When i retrieve a unit with a dot, the dot is place in the first index of my string.
Here is my UnitList table
And this is what I get when i select an item with pcs. unit. It should be "pcs.".
The dot(.) character is place in first index of my string. Same result with other unit with a character dot.
Here is my code:
Sub GetIngredientUnit(ByVal ProductName As String, ByVal Store As Label)
con.Close()
con.Open()
Query = "SELECT UnitList.UnitName FROM UnitList INNER JOIN ProductStock ON UnitList.[UnitID] = ProductStock.[UnitID] where ProductName = '" & ProductName & "'"
cmd = New OleDbCommand(Query, con)
Store.Text = cmd.ExecuteScalar
End Sub
And i call the code :GetIngredientUnit(ListViewInvStock.SelectedItems(0).Text, INVUnit) when the index of ListBox change
Change the Label's RightToLeft property to No. This property indicates if the language in use is a right-to-left script (e.g. Arabic).
If you want to align the text to the right hand side, set the TextAlign property instead.
I am coding in vb on visual studio 2012 and I need to create a query that pulls table data into a datagriddview. I have a textbox for user input and a combobox to set what the column name. Sort of like, "SELECT * FROM TITLES WHERE COMBOBOX LIKE TEXTBOX". I apologize if this question is old ground for you but I looked everywhere and couldn't find what I was looking for. Also I am a total newb so please speak slowly and in small words. Thanks in advance for your help.
You need to modify your SQL to be:
"SELECT * FROM TITLES WHERE " & ComboBox1.Text & " LIKE '%" & TextBox1.Text & "%'"
Deja Vu's answer should be ok. You may take it a step further, and try using a parameter instead of building the sql string directly from users' direct input, thus avoiding SQL Injection (which is a security risk):
Dim Sql As String = "SELECT * FROM MYTABLE WHERE " & ComboBox1.Text & " LIKE '%?%' "
Dim p As New OleDb.OleDbParameter : p.Value = Textbox1.text
Dim OleDBCommand As New OleDb.OleDbCommand(Sql, Connection)
OleDBCommand.Parameters.Add(p)
Dim da As New OleDb.OleDbDataAdapter(OleDBCommand)
Dim DT As New DataTable
da.Fill(DT)
(Note: I'm assuming this is an Application and users must choose an item from the combobox, and they cannot change the content of the combobox.)
Simple enough, I can't figure out how to add (that's +) an integer from a textbox to the integer in the SQL Field.
So for example, the SQL Field may have '10' in it and the textbox may have '5' in it. I want to add these numbers together to store '15' without having to download the SQL Table.
The textbox that contains the integer to be added to the SQL integer is tranamount.Text and the SQL Column in the SQL Table is #ugpoints. Please note, without the '+' - which is in the below code and is admittedly wrong- the value of tranamount.Text is added to the Table without an issue, but it simply replaces the original value; meaning the end result would be '5' in the SQL Field.
What would be the proper way to structure this? I've tried the below code, but that clearly doesn't work.
cmd = New SqlCommand("UPDATE PersonsA SET U_G_Studio=#ugpoints WHERE Members_ID=#recevierID", con)
cmd.Parameters.AddWithValue("#recevierID", tranmemberID.Text)
cmd.Parameters.AddWithValue("#ugpoints", + tranamount.Text) '<--- Value to add.
cmd.ExecuteNonQuery()
Newbies question I know, I'm new to SQL in vb.
You have to use the correct sql:
Dim sql = "UPDATE PersonsA SET U_G_Studio=U_G_Studio + #ugpoints WHERE Members_ID=#recevierID"
Also use the correct type with AddWithValue:
Using cmd = New SqlCommand(sql, con)
' use the using-statement to dispose everything that implements IDisposable, so also the connection '
cmd.Parameters.AddWithValue("#ugpoints", Int32.Parse(tranamount.Text))
' .... '
End Using
Take the current value of the U_G_Studio field, add the value of the parameter and reassign to U_G_Studio, but keep in mind that you need to pass the value as an integer because otherwise the AddWithValue will pass a string and you get conversion errors coming from the db.
cmd = New SqlCommand("UPDATE PersonsA SET U_G_Studio=U_G_Studio + #ugpoints " &
"WHERE Members_ID=#recevierID", con)
cmd.Parameters.AddWithValue("#recevierID", tranmemberID.Text)
cmd.Parameters.AddWithValue("#ugpoints", Convert.ToInt32(tranamount.Text))
cmd.ExecuteNonQuery()
The SQL you want is:
"UPDATE PersonsA SET U_G_Studio= (U_G_Studio + #ugpoints) " & _
"WHERE Members_ID=#recevierID"
what about
cmd.Parameters.AddWithValue("#ugpoints", (int)tranamount.Text)
....
cmd = New SqlCommand("UPDATE PersonsA SET U_G_Studio= SET U_G_Studio + #ugpoints WHERE Members_ID=#recevierID", con)
edit1: STEVE WAS FASTER!