I'm trying (using SQL and VB.Net) to get a list of dates and strings (representing a film name) using a SELECT command, and then look through each of the 'dates' in the list, one after the other. Like a 'FOR EACH' loop.
I'm not entirely sure how to do this, but here's what I have so far:
Dim Con = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;DataSource=ApplicationData.accdb;Persist Security Info=False;")
Con.Open() 'Open the connection
Dim Cmd As New OleDbCommand("SELECT fDateAdded, fName FROM Films", Con)
Cmd.CommandType = CommandType.Text
Dim Rdr As OleDbDataReader = Cmd.ExecuteReader()
Dim schemaTable As DataTable = Rdr.GetSchemaTable()
Dim row As DataRow
Dim column As DataColumn
For Each row In schemaTable.Rows
For Each column In schemaTable.Columns
' WHAT TO DO HERE?
Next
Next
How can I go about achieving my goal?
Your for-next loop should be something like this...
For Each row As DataRow In dtDataTable.Rows
If row.Item("fDateAdded") = *your match criteria* Then
*Do something - you can utilies* row.Item("fName") *if you need*
End if
Next row
The match criteria can of course be anything < <= > >= or a combination to give you a range etc.
Hope that helps.
Related
I'm wondering on whether its possible to check if a specific cell in a record is empty before attempting to collect its value and crashing the program if it cant be assigned to a variable.
Something along the lines of SELECT FirstNameColumn FROM tableNames WHERE LastNameColumn = "Smith", and to test if the FirstNameColumn has a value in it.
Im using VB.net, with the OleDB and an Access Database.
If you had some code that retrieved a record, and some of the values on the row might be null:
Public Sub ReadMyData(ByVal connectionString As String)
Dim queryString As String = "SELECT FirstNameColumn FROM tableNames WHERE LastNameColumn = 'Smith'"
Using connection As New OleDbConnection(connectionString)
Dim command As New OleDbCommand(queryString, connection)
connection.Open()
Dim reader As OleDbDataReader = command.ExecuteReader()
While reader.Read()
If Not reader.IsDbNull(0) Then
Console.WriteLine(reader.GetString(0))
End If
End While
reader.Close()
End Using
End Sub
A DataReader has an IsDBNull method hat will tell you whether a cell on a row is null.
Really though, using a DataReader is really low level and quite hard work. There are a lot easier ways to use a database. The next step up might reasonably be a dataadapter and datatable, offering a similar function:
Dim da as New OleDbDataAdapter("SELECT FirstNameColumn FROM tableNames WHERE LastNameColumn = 'Smith'", connStr)
DataTable dt = new DataTable()
custDA.Fill(dt)
For Each ro as DataRow in dt.Rows
If Not ro.IsNull("FirstNameColumn") Then
Console.WriteLine(ro("FirstNameColumn"))
End If
Next ro
TableAdapters another level of abstraction, removes all the horrible dealing with string column names amongst other things:
Dim ta as New PersonTableAdapter
Dim dt as PersonDataTable = ta.GetData()
For Each ro in dt
If Not ro.IsFirstNameColumnNull() Then
Console.WriteLine(ro.FirstNameColumn)
End If
Next ro
Entity Framework is probably equivalently high level, possibly higher:
Dim p as Person = context.Person.Where(Function(x) x.LastName = "Smith")
If p.FirstNameColumn Is Not Nothing Then
Console.WriteLine(p.FirstNameColumn)
End If
I want to double click a row in my datagrid and to transfer that data to my database, which then goes on to open a report based on that data just transferred.
If e.RowIndex >= 0 AndAlso e.ColumnIndex >= 0 Then
Dim selectedRow = DataGridView1.Rows(e.RowIndex)
End If
'Dim PtwNoData As String = String.Empty
Dim connection As SqlConnection
Dim Command As SqlCommand
Dim dt As New DataTable
Dim IdLast As Integer
Dim PTWNo As String
Dim Reader As SqlDataReader
connection = New SqlConnection("Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\IzzyM\Desktop\Developer\BIG\Permit Plus\Permit Plus\Database1.mdf;Integrated Security=True")
Dim GuiD As String
'GuiD = Me.DataGridView1.SelectedRows("GUID").Selected.
Try
connection.Open()
Dim Query As String
Query = "insert into PTWData * values ('" & Me.DataGridView1.SelectedRows(). & "')"
Command = New SqlCommand(Query, connection)
Reader = Command.ExecuteReader
connection.Close()
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
connection.Dispose()
End Try
'Form4.Dispose()
Dim f As New Form4()
f.TopMost = True
f.Show()
'Form4.Show()
End Sub```
You're wanting to add string values there, but the selected rows is a complicated object. It contains the resulting rows and each column within (along with many, many properties).
See below, where "ColumnNameIDK" is only one and you may have many to consider. This query will ultimately be a lot of inserts. (For safety sake, we may want to convert this to a parameterized query down the road)
...
Dim Query As String
Dim rows As DataGridViewSelectedRowCollection = MyDataGridView.SelectedRows
for each row in Me.DataGridView1.SelectedRows()
Dim myRow As DataRow = (TryCast(row.DataBoundItem, DataRowView)).Row
query &= "insert into PTWData * values ('" & myRow("ColumnNameIDK")& "');"
'this query appended on each pass
next
Command = New SqlCommand(Query, connection)
Reader = Command.ExecuteReader
I am trying to create a system that will load items from a database. There are two comboboxes; combobox1 which loads items from database table 1 and combox2 which loads items from database table 2.
Both tables are in the same database.
Here is was I tried but when I run the system I get this error:
(Conversion from string "SELECT * FROM dbo.Dishes" to type 'Long' is not valid.)
Here is the code I'm using:
Dim connection As New SqlConnection("Server = DESKTOP-1373H91; Initial Catalog = MealPreOrderSystem; Integrated Security = True")
connection.Open()
Dim query As String = "SELECT * FROM dbo.Dishes" And "SELECT * FROM dbo.Desserts"
Dim cmd As SqlCommand
cmd = New SqlCommand(query, connection)
Dim reader As SqlDataReader
reader = cmd.ExecuteReader
While reader.Read
cbxType.Items.Add(reader.Item("MealName"))
cbxType.Items.Add(reader.Item("DessertName"))
End While
connection.Close()
In VB.NET,AND is an operator.It is used to perform conjunction between either Booleans or Integers/Doubles/any numeric expression.Lets take your query string as an example :
Dim query As String = "SELECT * FROM dbo.Dishes" And "SELECT * FROM dbo.Desserts"
You are using AND here to join 2 sentences/strings which wouldn't result in anything rather it is trying to cast it as a Long.
Try to execute this command in SQL and you won't find any luck :(.
Your statements are correct :
SELECT * FROM dbo.Dishes
SELECT * FROM dbo.Desserts
But the way you are trying to achieve your goals is incorrect :(.
To get the data from the database into your combobox, what you can do is either use two comboboxes with separated SQL Queries/SQL Commands or you can use one combobox where you add data from both the databases but separate them with some special characters such as a comma ,
A sample may look like :
With one combobox
Dim cmd1 as new SqlCommand("SELECT * FROM dbo.Dishes",connection)
Dim dr as SqlDatareader = cmd1.ExecuteReader
While dr.Read
mycombo1.Items.Add(dr(0)) ' Here 0 is the column count,change it as required
End while
Dim cmd2 as new SqlCommand("SELECT * FROM dbo.Desserts",connection)
Dim dr2 as SqlDatareader = cmd2.ExecuteReader
While dr2.Read
mycombo2.Items.Add(dr2(0)) ' Here 0 is the column count,change it as required
End while
With 1 combobox
Here it gets a bit complicated.Firstly you need to populate your combobox from the data received from the first dataReader.Then, when the 2nd datareader is reading the data , you need to update the existing data/Item of the combobox keeping the existing data/item but adding new data/item to each existing data/item(separating them with ,).
Sample :
Dim i as Integer
Dim cmd1 as new SqlCommand("SELECT * FROM dbo.Dishes",connection)
Dim dr as SqlDatareader = cmd1.ExecuteReader
While dr.Read
mycombo1.Items.Add(dr(0))
End while
Dim cmd2 as new SqlCommand("SELECT * FROM dbo.Desserts",connection)
Dim dr2 as SqlDatareader = cmd2.ExecuteReader
While dr2.Read
mycombo1.Items(i) = myconbo1.Items(i) & "," & dr2(0)
i = i + 1
End while
Now, NOTE THAT I AM USING MULTIPLE DATAREADERS WITH THE SAME CONNECTION ,SO YOU MAY NEED TO INCLUDE MultipleActiveResultSets=True IN YOUR CONNECTION STRING or ENCLOSE THE DATAREADERS IN USING STATEMENTS or CALL dataReader.Close AFTER EACH DATAREADER HAS COMPLETED READING FROM THE DATABASE
This will solve your issue :)
Looks like you don't know how to write SQL queries (and your VB syntax itself looks faulty - string AND string?).
Dim connection As New SqlConnection("Server = DESKTOP-1373H91; Initial Catalog = MealPreOrderSystem; Integrated Security = True")
Dim query As String = <cmdString>
SELECT MealName as Name FROM dbo.Dishes
union
SELECT DessertName as Name FROM dbo.Desserts
</cmdString>
Dim cmd As SqlCommand
Dim reader As SqlDataReader
connection.Open()
cmd = New SqlCommand(query, connection)
reader = cmd.ExecuteReader
While reader.Read
cbxType.Items.Add(reader.Item("Name"))
End While
connection.Close()
Note: You are saying 2 comboboxes but your code seemed to be loading all the items to a single combobox. If you really need 2 comboboxes then use 2 SqlCommand and Reader loops (actually it would be better if you simply have used Linq for this).
You should be a bit more specific on what columns you are pulling from the 2 tables. if they are similar, you could write a sql query to UNION ALL the fields with a simple control to identify which record came from which table.
Example of SQL command string:
"SELECT 'M' AS Ctl, MealName AS aName FROM dbo.Dishes " &
"UNION ALL " &
"SELECT 'D' AS Ctl, DessertName AS aName FROM dbo.Desserts"
As mentioned by many here already, it seems like you are referencing only 1 ControlBox to list the fields returned cbxType
below is the reader (adapted to 2 ComboBoxes):
While reader.Read
Select Case reader.Item("Ctl")
Case "M"
cbxMType.Items.Add(reader.Item("aName"))
Case "D"
cbxDType.Items.Add(reader.Item("aName"))
End Select
End While
Hope this helps
I'm having trouble with code that loops through the tables that contain TRelationCode. When it finds one it has to get the RelationCode from it and then convert it into the new RelationCode and update it to the new one.
To create the new RelationCode I've made a function Called MakeRelationCode(OldRelation). I have this code to loop through the tables:
Dim query As String = "use fmsStage; SELECT * FROM INFORMATION_SCHEMA.columns WHERE COLUMN_NAME = 'TRelationcode'"
Dim myCmd As SqlDataAdapter = New SqlDataAdapter(query, con)
Dim myData As New DataSet()
myCmd.Fill(myData)
For Each table As DataTable In myData.Tables
For Each row As DataRow In table.Rows
For Each col As DataColumn In table.Columns
Next
Next
Next
But now I need to update the old codes to the new ones.
I prefer simple SQL commands and a little vb logic thus I skipped the SqlDataAdapter part. This will only cost performance and is only necessary if you display something in a grid and want two-way-binding.
The following code is untested and typed blind so please check for typos etc.
I put everything in one method.
Dim tableNames As New List(Of String)
'Key: Old code, Value: New code'
Dim trelationcodes As New Dictionary(Of String, String)
Using conn As New SqlClient.SqlConnection("YourConnectionString") 'Change connection string to your needs'
Dim qTableNames = "SELECT TABLE_NAME FROM INFORMATION_SCHEMA.columns WHERE COLUMN_NAME = 'TRelationcode'"
conn.Open()
'Get table names with TRelationcode column'
Using commTableNames As New SqlClient.SqlCommand(qTableNames, conn)
Dim dataReader = commTableNames.ExecuteReader()
While dataReader.Read()
tableNames.Add(dataReader.GetString(0))
End While
End Using
'Select all distinct old TRelationcode which will be updated'
Dim qTrelationcodesOld = "SELECT DISTINCT TRelationcode FROM {0}"
For Each tableName In tableNames
'Get all old TRelationcodes from table found previuosly'
Using commTrelationcodesOld As New SqlClient.SqlCommand()
commTrelationcodesOld.Connection = conn
commTrelationcodesOld.CommandText = String.Format(qTrelationcodesOld, tableName)
Dim dataReader = commTrelationcodesOld.ExecuteReader()
While dataReader.Read()
Dim code = dataReader.GetString(0)
If Not trelationcodes.ContainsKey(code) Then
trelationcodes.Add(code, "") 'Value will be set later'
End If
End While
End Using
'Get new TRelationcodes'
For Each tRelCodeOld In trelationcodes.Keys
trelationcodes(tRelCodeOld) = MakeRelationCode(tRelCodeOld)
Next
'Set new TRelationcodes'
Dim uTRelationcode = "UPDATE {0} SET TRelationcode = #newCode WHERE TRelationcode = #oldCode"
For Each tRelCodes In trelationcodes
Using commTrelationcodesNew As New SqlClient.SqlCommand()
commTrelationcodesNew.Connection = conn
commTrelationcodesNew.CommandText = String.Format(uTRelationcode, tableName)
commTrelationcodesNew.Parameters.Add("#oldCode", SqlDbType.VarChar).Value = tRelCodes.Key 'Varchar correct?'
commTrelationcodesNew.Parameters.Add("#newCode", SqlDbType.VarChar).Value = tRelCodes.Value 'Varchar correct?'
commTrelationcodesNew.ExecuteNonQuery()
End Using
Next
Next
End Using
The code is far away from being optimal, e.g. I skipped exception handling.
The most concerning part is your MakeRelationCode function. If the logic inside could be written in T-SQL in a Stored Procedure, the overall coding would also be simplified.
I would like to do a populate a column in my listbox for each field in my Access Database.
Right now I have to manually add the field:
QUERBOX.Columns.Add("Requestor Name", 200, HorizontalAlignment.Left)
How can I adapt my code below to automatically add columns each time I run the sub?
Dim queryString As String = "SELECT * FROM Table1;"
Dim connection As OleDbConnection
Dim command As OleDbCommand
Dim data_reader As OleDbDataReader
querbox.clear
connection = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\apt.accdb")
connection.Open()
command = New OleDbCommand(queryString, connection)
data_reader = Command.ExecuteReader
If data_reader.HasRows Then
While data_reader.Read
Dim newitem As New ListViewItem()
newitem.Text = data_reader.GetValue(0) 'first column
newitem.SubItems.Add(data_reader.GetValue(1)) 'second column
QUERBOX.Items.Add(newitem)
End While
End If
As Plutonix suggested in comments, a DataGridView would probably be best suited, but for the sake of answering the question here's how I've done something similar:
connection.Open()
'' Fill a DataTable with all of the Column schema for the given table of 'Table1'
Dim schemaTable As DataTable = connection.GetSchema("Columns", New String() {Nothing, Nothing, "Table1", Nothing})
'' Iterate through each column in the Schema Table
For i = 0 To schemaTable.Rows.Count - 1 Step 1
'' Declare a new item for the list
Dim newItem As New ListViewItem()
newItem.Text = schemaTable.Rows(i)!COLUMN_NAME.ToString()
newItem.SubItems.Add(schemaTable.Rows(i)!COLUMN_NAME.ToString()
'' Add new item to the interface
QUERBOX.Items.Add(newItem)
Next
connection.Close()
This has helped me in projects where the user is familiar with the database structure and may need to select the fieldname as part of the business logic. For example, allowing someone with little database knowledge to standardize the records within a given field.