I have this part of code:
Dim SqlCommand_customer As New SqlCommand("selectcustomer", conn.con)
SqlCommand_customer.CommandType = CommandType.StoredProcedure
Dim da_customer As New SqlDataAdapter
Dim SqlDataAdapter_customer As New SqlDataAdapter(SqlCommand_customer)
Dim ds_customer = New DataSet()
SqlDataAdapter_customer.Fill(ds_customer, "customer")
DataGridView_customer.DataSource = ds_customer.Tables("customer")
So I want to know what does "customer" stands for in the last two lines
There is nothing named customer in the whole file
and MSDN states that the second parameter in Fill must be of type iDataReader:
dataReader
Type: System.Data.IDataReader
An instance of IDataReader.
The SqlDataAdapter class derives from DbDataAdapter that has a method overload for Fill that takes as second parameter a string.
This string is the name that will be assigned to the table created to store your records or, if you have already tables in the dataset, it is the name of a preexisting table wich will be loaded/refreshed with the records returned by the command.
Of course the syntax in
DataGridView_customer.DataSource = ds_customer.Tables("customer")
is the way in which you reference this table by its name (that would be the same as ds_customer.Tables(0))
The second argument to the fill command is the name of a table.
You are looking at the wrong reference. You want the Fill command off of the SQLDataAdapter.
Related
Private Sub ButtonSubmitID_Click(sender As Object, e As EventArgs) Handles ButtonSubmitID.Click
Dim comm As New SqlCommand
Dim conn As New SqlConnection
conn.ConnectionString = "Data Source = localhost\SQLEXPRESS; Initial Catalog = test2Forms; Integrated Security = SSPI;"
comm.Connection = conn
Dim ID = TextBoxID.Text
comm.Parameters.AddWithValue("#ID", ID)
Dim adapter As SqlDataAdapter = New SqlDataAdapter(comm.CommandText, comm.Connection)
comm.CommandText = "SELECT * FROM withActivityLog3 WHERE ID = #ID"
Dim records As DataSet = New DataSet
adapter.Fill(records)
DataGridView2.DataSource = records
End Sub
CommandText property has not been initialized is the error I am receiving. I am able to pull all the data from the database into the GridView on the Form Load but when I try to narrow it down to one ID using a WHERE clause on the button trigger, it comes up with the above error. I've used the debugger to trace through one step at a time and the command and connection strings look correct. I've also successfully duplicated the query on my database using the SQL Server command line. I'm searching on a primary key (ID) so the expected results would be one uniquely identified row from the database.
As for the problem you know you have:
' initialize DataAdapter with (EMPTY) commandtext
Dim adapter As SqlDataAdapter = New SqlDataAdapter(comm.CommandText, comm.Connection)
' initialize Command Text
comm.CommandText = "SELECT * FROM withActivityLog3 WHERE ID = #ID"
When you pass the CommandText to the DataAdapter, it is empty because you havent set it yet which results in the error.
There is a fair amount of inefficiency in your code though. Rewritten:
' form level conn string
Private TheConnString As String = "Data Source = localhost\..."
Private Sub ButtonSubmitID_Click(sender ...
Dim dt As New DataTable
Using dbcon As New MySqlConnection(TheConnString)
Using cmd As New MySqlCommand("select * from Sample where Id = #id", dbcon)
cmd.Parameters.Add("#id", MySqlDbType.Int32).Value = Convert.ToInt32(TextBox2.Text)
dbcon.Open()
dt.Load(cmd.ExecuteReader)
dgvA.DataSource = dt
End Using
End Using
End Sub
Note: this uses MySQL but the concepts are the same for Sqlite, Access, SQL Server etc
There is no need to type or paste the connection string and over everywhere it is used. One form level variable will allow DRY (Dont Repeat Yourself) code.
Anything which implements the Dispose() method should be disposed of. That includes nearly all the DB Provider objects. The Using statement allows you to declare and initialize an object and at the End Using it is disposed of. Failing to Dispose of things can cause leaks and even run out of connections or resources to create things like DB Command objects.
There is no need to create a local DbDataAdapter. These are very powerful and useful critters meant to do much more than fill a DataTable. If that is all you are doing, you can use ExecuteReader method on the DbCommand object.
Nor do you need a local DataSet. Contrary to the name, these do not hold data, but DataTables. Since there is only one and it is local (goes out of scope when the method ends), you dont need a DataSet to store it.
The Add method should be used rather than AddWithValue. The code above specifies the datatype for the parameter so there is no guesswork required of the compiler. Of course with that comes the need to convert the text to a number...
...Since this is user input, you should not trust the user, so Integer.Tryparse would be more appropriate: I like pie will not convert to an integer. Data Validation is something you should do before you commence the DB ops.
Dim ID = TextBoxID.Text as used is pointless code. You do not need to move the textbox text into a new variable in order to use it. However, ID might be used to store the integer value
This is what I presently have
Dim myDataTable As New DataTable
Dim sqlConnection1 As New SqlConnection("myconnectionstring")
Dim cmd As New SqlCommand
Dim reader As SqlDataReader
Dim allSelectedTexts As New List(Of String)
cmd.CommandText = "SELECT * FROM table WHERE parameter=#parameter"
cmd.Parameters.AddWithValue("#parameter", parameter)
cmd.Connection = sqlConnection1
sqlConnection1.Open()
reader = cmd.ExecuteReader()
myDataTable.Load(reader)
sqlConnection1.Close()
lbProduct.DataSource = myDataTable
lbProduct.DataTextField = "product_name"
lbProduct.DataValueField = "product_id"
lbProduct.DataBind()
What I want to do is to query data to add onto this using a new parameter, how would I do that?
I need to get another table and append It onto this one
This is in a multiselect listbox, the first click will get data to add into a datasource, the second click will get other data. I was thinking I could loop through the elements I have selected then add it to the table before I set the datasource, but I don't know how to append to the table
If I understand you correctly, it seems that you just need to know how to append to the datatable before setting the datasource.
You said you wanted to get another table appended to this one. If the schemas are the same (or very similar) you could use the DataTable.Merge method to bring the data together.
Alternatively if your other data is not in the same format, is not in a datatable, or otherwise you would prefer not to use this method, you could use the DataTable.Rows.Add method to write in the data line by line. In this case you would compile your data into an array, such as the following:
myDataTable.Rows.Add(value1, value2, value3, etc...)
Another option might be to bring your other data into another datatable if you wanted to make use of the DataTable.Merge method.
I hope this helps!
DataTable.Merge
DataTable.Rows.Add
I use below code in try catch block but it gives exception"'table' argument cannot be null. Parameter name: table" .My table name is caste and that table two columns are there srno and castename .But it say that my table has no data.Memory table is a datatable.
Dim Dset As New DataSet()
Dset = New DataSet()
Dset.Tables.Add(MemoryTable)
DataGridView1.DataSource = Dset.Tables("caste")
I tried data connect with database with using datasource but it gives service pack 1 error
'One is to use data binding on your TextBox controls and assigning the same DataSource.but its gives error
You don't show the definition of MemoryTable, but you do say it's a data table. If it's an object of type System.Data.DataTable, then it will have a property called TableName.
When you access a DataTable in a DataSet with a string index value, the value you are passing is the table's TableName property. So Dset.Tables("caste") is looking for a DataTable whose TableName property is set to "caste". If it can't find one, it will return Null. That looks like what's happening.
So set MemoryTable.TableName to "caste" and the error may go away.
I assume that MemoryTable actually has rows in it? If not, that may be a reason why you're getting the message about your table having no data.
So your code should look something like this:
Dim Dset As New DataSet() ' You don't have to do a separate assignment to Dset
' if you use New in the declaration, so we can omit that line.'
MemoryTable.TableName = "caste"
Dset.Tables.Add(MemoryTable)
DataGridView1.DataSource = Dset.Tables("caste")
And, actually, you can use MemoryTable as your data source without having to add it to a DataSet, unless you need to for some other reason.
DataGridView1.DataSource = MemoryTable
I hope this helps.
Im using VB.net and I have a variable that contains a string which is the name of another variable. I want to access that variable based off of that string. The scenario goes like this
I am doing a log DataTable with variable name "LogChanges"
Now I have a DataTable variable name "dtbEmployee"
the value "dtbEmployee" will be stored in DataTable "LogChanges" as string
Now
while i loop through the "LogChanges" DataTable and get the "dtbEmployee" in string. Is there a way to use this string to point back to the "dtbEmployee" DataTable
Something like this
For Each dr As DataRow In LogChanges.Select("", "DtbId")
If dr.Item("RecordSeQ") > 0 Then
Dim tempDataTable As DataTable
tempDataTable = "Convert dr.Item("dtbNAme")" to DataTable code
End If
Next
Note: RecordSEQ is just a counter to see how many records have been modified for this table
You would need to store the DataTable against that name somewhere, e.g. the Tables collection of a DataSet or a Dictionary. If the variable is a field and you have the object that has the correct DataTable assigned to that field then you could use Reflection but that would be cumbersome at best. The variable is not the DataTable so you have to some actual relationship to use to get the DataTable via the use of the name.
I would like to fill a datatable with results from a SQL select statment but using a transaction. The reason that I am using a transaction is because I have a list of names (as a datatable), and I want to iterate through the list of names and select the database rows where the name = the name on the list. There are 500,000 names in the database and I only want to retreive the relevant rows. I have the code for the procedure as I think it should look like (untested) BUT I dont know HOW to place the data into a datatable .... so Im missing something where I declare the datatable and the 'fill' of that table , could someone help with this ? Or suggest how else I can get the information out of the batabase without looking up each name individually.
Using connection As New SQLite.SQLiteConnection(R2WconectionString)
connection.Open()
Dim sqliteTran As SQLite.SQLiteTransaction = connection.BeginTransaction()
Try
oMainQueryR = "SELECT NameID, Address, Ocupation FROM Employees Where Name= :Name"
Dim cmdSQLite As SQLite.SQLiteCommand = connection.CreateCommand()
With cmdSQLite
.CommandType = CommandType.Text
.CommandText = oMainQueryR
.Parameters.Add(":Name", SqlDbType.VarChar)
End With
'Prevent duplicate selects by using a dictionary
Dim NameInalready As New Dictionary(Of String, String)
For Each row As DataRow In TheLIST.Rows
If NameInalready.ContainsKey(row.Item("Name")) Then
Else
NameInalready.Add(row.Item("Name"), "")
cmdSQLite.Parameters(":Name").Value = row.Item("Name")
cmdSQLite.ExecuteNonQuery()
End If
Next
sqliteTran.Commit()
Catch ex As Exception
End Try
End Using
First, you don't need a transaction because you aren't updating the database.
Second, depending on the possible number of Names in TheLIST, it might be worthwhile for you to change the name selector to IN (i.e. SELECT * FROM Employees WHERE Name IN ('name1', 'name2'). However, if you expect more than about 10, this is probably not worth trouble.
Finally, you need to create a new DataTable to hold the results. Then you need to create a DataAdapter passing cmdSqlLite as the constructor parameter. And finally, replace your ExecuteNonQuery with DataAdapter.Fill(DataTable).
For example (after Dim cmdSQLite):
Dim oDataTable As New DataTable("Employees")
Dim oAdapter As New SqliteDataAdapter(cmdSQLite)
and replacing the ExecuteNonQuery line with:
oAdapter.Fill(oDataTable)
I will qualify this code by saying it may need some tweaks. I only work with class objects and collections, so my preference would have actually been to load a collection of Employee class instances.
I would have done that by replacing ExecuteNonQuery with ExecuteReader and then the loading the read data into a new class instance. This type of approach resolves various issues with serializing the data across service boundaries (i.e. Xml for web services) and also lets you embed business logic, if needed, into the classes.