so I'm using SQLite in a VB.net project with a populated database. I'm using the Microsoft.Data.Sqlite.Core and System.Data.SQLite NuGet package libraries. So the problem presents when I'm trying to get the result of a query. At first the SQLiteDataReader gets the response and all the elements of the desired table. I know this cause in the debugger I have a breakpoint after the setting the object and when I check the parameters of the SQLiteDataReader object the Result View shows all the elements of my table, but as soon as I remove the mouse from the object and check it again the Result View turns out empty, without even resuming with the next line of code. Does anyone know if its a known bug or something cause Ive used this exact method of querying a table in another project and it works.
The code:
Public Function RunQuery(com As String)
If CheckConnection() Then
command.CommandText = com
Dim response As SQLiteDataReader
response = command.ExecuteReader
Dim len As Integer = response.StepCount
Dim col As Integer = response.FieldCount
Dim resp(len, col) As Object
For i = 0 To col - 1
Using response
response.Read()
For j = 0 To len - 1
resp(i, j) = response.GetValue(j)
Next
End Using
Next
Debugger with populated result view
Debugger with empty result view
edit: added the for loop to show that its not only on the debugger that the result view is empty. When using response.Read() it throws an exception "System.InvalidOperationException: 'No current row'"
As I have told you in the comment, a DataReader derived class is a forward only retrieval object. This means that when you reach the end of the records returned by the query, that object is not capable to restart from the beginning.
So if you force the debugger to enumerate the view the reader reaches the end of the results and a second attempt to show the content of the reader fails.
The other part of your problem is caused by a misunderstanding on how to work on the reader. You should loop over the Read result not using a StepCount property. This property as far as I know, is not standard and other data providers don't support it. Probably it is present in the SQLite Provider because for them it is relatively easy to count the number of records while other providers don't attempt do calculate that value for performance reasons.
However, there are other ways to read from the reader. One of them is to fill a DataTable object with its Load method that conveniently take a DataReader
Dim data As DataTable = New DataTable()
Using response
data.Load(response)
End Using
' Now you have a datatable filled with your data.
' No need to have a dedicated bidimensional array
A DataTable is like an array where you have Rows and Columns instead of indexes to iterate over.
After going over multiple questions/answers on Stackoverflow and other boards I'm still lost on why I can't update an Access database from a datatable. I'm trying to take data from a datatable and insert that data into an Access table if it is blank, and replace the table if it already has data. I can successfully replace the table, but the data from the datatable does not get added.
However, the method which I'm using does not appear to work. My datatable comes from a bound datagridsource and the Access layer is called like this:
ConnectedDB.UpdateTable(DBTable, bsDataSource.DataSource)
Where ConnectedDB is the Access Layer class, DBTable is the string containing the Access table name, and bsDataSource is the bound data. As you can see, I passed the .Datasource to turn it into a datatable.
Here is the original (pre-Jan 29th) section of my work to add the datatable back into the Access table:
Public Function UpdateTable(strTable As String, dgDataTable As DataTable) As Boolean
Dim DS As New DataSet
dgDataTable.TableName = strTable
DS.Tables.Add(dgDataTable)
Using OpenCon = New OleDb.OleDbConnection(strConnectionString)
Using DataAdapter As New OleDbDataAdapter("SELECT * FROM " & strTable, OpenCon)
Dim DBcmd As OleDbCommandBuilder = New OleDbCommandBuilder(DataAdapter)
DBcmd.QuotePrefix = "["
DBcmd.QuoteSuffix = "]"
DataAdapter.UpdateCommand = DBcmd.GetUpdateCommand()
Try
OpenCon.Open()
DataAdapter.Fill(DS.Tables(strTable))
If DataAdapter.Update(DS.Tables(strTable)) > 0 Then
Return True
Else Return False
End If
Catch exo As Exception
MessageBox.Show(exo.Message)
Return False
End Try
End Using
End Using
End Function
My function tries to update an existing Access table with the name represented as strTable with the information in the datatable, dgDataTable from a datagridview. Each run hits the update check > 0 and returns a false which means syntax wise it should be working (i.e. no error messages). I have traced the table and it has all the data it should have (so the information is getting passed correctly from the grid through the update commands). I was playing with applying it in a dataset but I'm not sure I really need that.
I was tracing the variables through the update method and I think I found out why it won't update but I'm not sure what to do about it. The query it comes up with is like this:
UPDATE [RtoC] SET [R] = ?, [C] = ?, [Type] = ?, [Unknown] = ? WHERE (([R] = ?) AND ([C] = ?) AND ([Type] = ?) AND ((? = 1 AND [Unknown] IS NULL) OR ([Unknown] = ?)))
The Access table name is RtoC with fields R, C, Type, and unknown.
I'm thinking the "?" are not getting filled in causing the query to just not apply data back to Access. I'm not sure though how to set those items.
EDIT 1/29/20: I used the code changes I and jmcihinney document below and it does insert the lines into the Access table. This edit alters the question to be more specific about what I'm am trying to do, and how the datatable is created. Hopefully this clears up some wording on my part and provides some basis for the alteration of the row state.
The issue is that the Fill method of that data adapter calls AcceptChanges on the DataTable after populating it, thus there are no changes to save when you call Update.
That call to Fill shouldn't be there anyway though, because you don't want to retrieve any data, just save changes. You've got a whole lot of pointless code there. It should look more like this:
Public Function UpdateTable(strTable As String, dgDataTable As DataTable) As Boolean
Using DataAdapter As New OleDbDataAdapter("SELECT * FROM " & strTable, strConnectionString)
Dim DBcmd As OleDbCommandBuilder = New OleDbCommandBuilder(DataAdapter)
DBcmd.QuotePrefix = "["
DBcmd.QuoteSuffix = "]"
Try
Return DataAdapter.Update(dgDataTable) > 0
Catch exo As Exception
MessageBox.Show(exo.Message)
Return False
End Try
End Using
End Function
I took another tack at manipulating the database and in looking that up, I found the answer provided by jmcilhinney back in 2014! [Bulk Insert From DataTable to Access Database
In a for each loop across the rows of my datatable I set this:
row.SetAdded()
If I was filling I would have done something like:
DataAdapter.AcceptChangesDuringFill = True
Before the Fill command.
Unless this method has changed or there is a better way, I'll mark the link as the answer.
Thanks jmcilhinney....twice!
I'm currently trying to figure out the basics of remote function calls via vb .NET. I feel pretty helpless however, because their just isn't any useful documentation for the most simple of tasks.
What I'm trying to do atm is starting the transaction CO13, write the confirmation number in the appropriate field and cancel the order. Even this simple tasks turned out to be a pain in the ass. I'm still not sure how to access and modify the contents of a specific field. There are some examples with tables for excel in the net, but hat's about it. What I have so far is this (login is working and in another function):
Public Function stornieren() As Boolean
Dim ordernr As String
Dim confirmationnr
Dim confirmation As Object
Dim R3 As Object
Dim CO13 As Object
Dim result
R3 = CreateObject("SAP.Functions")
ordernr = TextBox3.Text
confirmationnr = TextBox4.Text
CO13 = R3.Add("RFC_CALL_TRANSACTION_USING")
CO13.exports("TCODE") = "CO13"
CO13.exports("MODE") = "S"
confirmation = CO13.exports("RUECK")
confirmation.value = confirmationnr
result = CO13.call
End Function
RUECK is the Field Name. I want to write the value of "confirmationnr" into the field RUECK. "confirmation.value = confirmationnr" throws the error message "the object variable could not be determined" and "NullReferenceException" was not handled. Sounds to me like the object is empty.
Thanks in advance.
EDIT: Now trying via BAPIs and particularly BAPI_PRODORDCONF_CANCEL. I have no idea about the syntax though. Any help would be appreciated.
I have a Dynamic Data LINQ to SQL ASP.Net Website in VB.NET, and am having a little trouble with Sorting of my GridView and a Search routine I have implemented. On Page_Load, the GridView is sorted by a field (Departments.department) in ASC order. However, when I perform a search using the code below, I get an error
The Data Source Does Not Support Sorting.
I'm assuming the problem comes when the Page_Load event tries to sort the data after a Search is made, because of the DataSource/ID.
Dim button = DirectCast(sender, Button)
If button.ID = btnMultiColumnSearchClear.ID Then
txbMultiColumnSearch.Text = [String].Empty
Else
Using Data As New wcPhonesDataContext()
Dim EmployeeNameString As String = txbMultiColumnSearch.Text
Dim SearchResults = Data.Employees.Where(Function(Employees) Employees.Employee.Contains(EmployeeNameString))
GridView1.DataSourceID = ""
GridView1.DataSource = SearchResults
GridView1.DataBind()
End Using
End If
SOLVED, but now I have a new problem, here is the code I used to solve this issue...
Dim button = DirectCast(sender, Button)
If button.ID = btnMultiColumnSearchClear.ID Then
txbMultiColumnSearch.Text = [String].Empty
Else
Using Data As New wcPhonesDataContext()
Dim EmployeeNameString As String = txbMultiColumnSearch.Text
Dim SearchResults = Data.Employees.Where(Function(Employees) Employees.Employee.Contains(EmployeeNameString))
GridView1.Sort("", SortDirection.Ascending)
GridView1.DataSourceID = ""
GridView1.DataSource = SearchResults
GridView1.DataBind()
End Using
End If
I have created a new error though. It occurs if I perform a second search without going BACK to the Employees table.
'GridView1' fired event Sorting which wasn't handled.
If you use a SqlDataSource and connect the gridview to the data source with a datasourceid, then sorting is done for you magically. You don't have to do anything to support it.
But if set the datasource to some object that you have created in code, sorting does NOT magically happen for you. When the user clicks on a column head, this fires an OnSorting event. You have to write code to handle the event. Typically this mean regenerating the data in the desired order, or regenerating the data and then sorting it.
For example, if you generate the data with a SQL query, I sometimes create a function that runs the SQL query and returns a DataSet. This function takes the sort field as a parameter, which it pastes into the SQL query. Then for the initial display call this function passing in the default sort order, and for the OnSorting call this function passing in the desired sort field.
I am doing windows appliction in vb.net. i have customer object contains save method. how do i generate insert query?
I need to save the object in relational database (SQL server). I need to know which is the correct way of doing the insertion ie,. Inside the save method i have written the SQL statement to save the object. Is it the correct way?
Thanks
A simple INSERT statement for SQL takes this basic form:
INSERT INTO [tablename] ( [column1], [column2], ... ) VALUES ( [value1], [value2], ...)
So, we obviously need to know about the database table you are using: what columns it has. We also need to know about the class: what properties it has. Finally, we need to know about the data types for the table columns and class properties, and how the properties will map to the columns. For very simple objects the names and types will just line up. But in other cases your class may itself contain a collection (or several) that would mean inserting data into more than one table.
After all this is determined, we still need two things: connection information for the database (usually distilled down into a single connection string) and whether or not you are concerned that your class instance may have been saved previously, in which case you want to build an UPDATE statement rather than INSERT.
Assuming you can answer all of that in a satisfactory manner, your VB.Net code will look something like this (of course substituting your specific column, property, type, and connection information where appropriate):
Public Class Customer
Public Sub Save()
DAL.SaveCustomer(Me)
End Sub
' ...'
End Class
.
' a VB Module is a C# static class'
Public Module DAL
Private ConnString As String = "Your connection string here"
Public Sub SaveCustomer(ByVal TheCustomer As Customer)
Dim sql As String = "" & _
"INSERT INTO [MyTable] (" & _
"[column1], [column2], ..." & _
") VALUES (" & _
"#Column1, #Column2, ... )"
Using cn As New SqlConnection(ConnString), _
cmd As New SqlCommand(sql, cn)
cmd.Parameters.Add("#column1", SqlDbTypes.VarChar, 50).Value = TheCustomer.Property1
cmd.Parameters.Add("#column2", SqlDbTypes.VarChar, 1000).Value = TheCustomer.Property2
cn.Open()
cmd.ExecuteNonQuery()
End Using
End Sub
End Module
I know you've already heard that separating out your database code is the "right thing to do"tm, but I thought you might also want some more specific reasons why you would want to structure your code this way:
Your connection string is kept in one place, so if your database server moves you only need to make one change. Even better if this is it's own assembly or config file.
If you ever move to a completely different database type you only need to change one file to update the program.
If you have one developer or a DBA who is especially good with sql, you can let him do most of the maintenance on this part of the app.
It makes the code for your "real" objects simpler, and therefore easier to spot when you make a logical design error.
The DAL code might eventually be re-usable if another application wants to talk to the same database.
If you use an ORM tool most of the DAL code is written for you.
There's a few issues here. First, exactly where are you saving this? You say SQL, but is it a SQL Server, an instance of SQL Express, a Local Data Cache (SQL CE 3.5) or saving via a Web Service to talk to your SQL SERVER. These different data sources have different connectivity options/requirements, and in the case of SQL CE there's a few other "gotchas" involved in the SQL itself.
Second, are you sure you want to save data into a relational datastore like SQL Server? Consider, you could use XML, a data file (text, CSV. etc) or even a custom binary file type instead.
Since you're working on a windows application, you have a bunch of options on where and how to save the data. Until you know where you want to put the data, we'd be hard pressed to help you do so.
I agree with Mike Hofer. Keeping your class that does your retrieval and persisting of object separate from your business classes is key to having a flexible and robust design. This is the kind of code you want to be seeing in your GUI or Business layer:
//Populate Customer Objects List with data
IList<Customer> customerList = new List<Customer>()
Customer newCustomer1 = new Customer();
newCustomer.Name = "New Name"
newCustomer.email ="abcd#abcd.com"
customerList.Add(newCustomer1)
//DAL calls
DataAccessClass dalClass = new DataAccessClass ();
dalClass.InsertCustomers(customerList);
Inside your DALClass there should be a method called InsertCustomers(IList customers) and it should have the following code:
Public Function InsertCustomers(ByVal objectList As IList(Of Customer)) As Integer
Dim command As IDbCommand = Nothing
Dim rowsAffected As Integer = 0
Dim connection As IDbConnection = New System.Data.SqlClient.SqlConnection(Me.ConnectionString)
Try
connection.Open
Dim e As IEnumerator = objectList.GetEnumerator
Do While e.MoveNext
command = connection.CreateCommand
command.CommandText = "insert into dbo.Customer(CustomerID,CustomerGUID,RegisterDate,Password,SiteID,Las"& _
"tName,FirstName,Email,Notes,BillingEqualsShipping,BillingLastName) values (#Cust"& _
"omerID,#CustomerGUID,#RegisterDate,#Password,#SiteID,#LastName,#FirstName,#Email"& _
",#Notes,#BillingEqualsShipping,#BillingLastName)"
System.Console.WriteLine("Executing Query: {0}", command.CommandText)
Dim paramCustomerID As IDbDataParameter = command.CreateParameter
paramCustomerID.ParameterName = "#CustomerID"
command.Parameters.Add(paramCustomerID)
Dim paramCustomerGUID As IDbDataParameter = command.CreateParameter
paramCustomerGUID.ParameterName = "#CustomerGUID"
command.Parameters.Add(paramCustomerGUID)
Dim paramRegisterDate As IDbDataParameter = command.CreateParameter
paramRegisterDate.ParameterName = "#RegisterDate"
command.Parameters.Add(paramRegisterDate)
Dim paramPassword As IDbDataParameter = command.CreateParameter
paramPassword.ParameterName = "#Password"
command.Parameters.Add(paramPassword)
Dim paramSiteID As IDbDataParameter = command.CreateParameter
paramSiteID.ParameterName = "#SiteID"
command.Parameters.Add(paramSiteID)
Dim paramLastName As IDbDataParameter = command.CreateParameter
paramLastName.ParameterName = "#LastName"
command.Parameters.Add(paramLastName)
Dim paramFirstName As IDbDataParameter = command.CreateParameter
paramFirstName.ParameterName = "#FirstName"
command.Parameters.Add(paramFirstName)
Dim paramEmail As IDbDataParameter = command.CreateParameter
paramEmail.ParameterName = "#Email"
command.Parameters.Add(paramEmail)
Dim paramNotes As IDbDataParameter = command.CreateParameter
paramNotes.ParameterName = "#Notes"
command.Parameters.Add(paramNotes)
Dim paramBillingEqualsShipping As IDbDataParameter = command.CreateParameter
paramBillingEqualsShipping.ParameterName = "#BillingEqualsShipping"
command.Parameters.Add(paramBillingEqualsShipping)
Dim paramBillingLastName As IDbDataParameter = command.CreateParameter
paramBillingLastName.ParameterName = "#BillingLastName"
command.Parameters.Add(paramBillingLastName)
Dim modelObject As Customer = CType(e.Current,Customer)
paramCustomerID.Value = modelObject.CustomerID
paramCustomerGUID.Value = modelObject.CustomerGUID
paramRegisterDate.Value = modelObject.RegisterDate
If IsNothing(modelObject.Password) Then
paramPassword.Value = System.DBNull.Value
Else
paramPassword.Value = modelObject.Password
End If
paramSiteID.Value = modelObject.SiteID
If IsNothing(modelObject.LastName) Then
paramLastName.Value = System.DBNull.Value
Else
paramLastName.Value = modelObject.LastName
End If
If IsNothing(modelObject.FirstName) Then
paramFirstName.Value = System.DBNull.Value
Else
paramFirstName.Value = modelObject.FirstName
End If
If IsNothing(modelObject.Email) Then
paramEmail.Value = System.DBNull.Value
Else
paramEmail.Value = modelObject.Email
End If
If IsNothing(modelObject.Notes) Then
paramNotes.Value = System.DBNull.Value
Else
paramNotes.Value = modelObject.Notes
End If
paramBillingEqualsShipping.Value = modelObject.BillingEqualsShipping
If IsNothing(modelObject.BillingLastName) Then
paramBillingLastName.Value = System.DBNull.Value
Else
paramBillingLastName.Value = modelObject.BillingLastName
End If
rowsAffected = (rowsAffected + command.ExecuteNonQuery)
Loop
Finally
connection.Close
CType(connection,System.IDisposable).Dispose
End Try
Return rowsAffected
End Function
It is painful to write the DAL code by hand, but you will have full control of your DAL, SQL and Mapping code and changing any of those will be a breeze in the future.
If you don't feel like to write all the DAL Code by hand, you can get a CodeGenerator like Orasis Mapping Studio to generate exactly the same code shown without writing anything. You just need to build your SQL in the tool, map the properties to the paramaters and you are done. It will generate all the rest for you.
Good luck and happy DAL coding!
I'm with Stephen Wrighton. There are a LOT of variables here, and a lot of unanswered questions. If it's SQL, is it even a Microsoft dialect of SQL? Is it Oracle? MySQL? Something else?
In any event, my personal preference is to avoid building SQL in an application if I can, and invoke a stored procedure, even for inserts and updates. Then I pass the arguments for the procedure to the ADO.NET command object. I have this insane idea in my head that SQL belongs in the database. Perhaps that comes from all that time I spent debugging horrifically written ASP code that spliced SQL strings together back in the Dot Com era. (Never again.)
If you feel it's absolutely necessary to do so, meet the System.Text.StringBuilder class. Learn it. Love it. Make it your best friend.
UPDATE:
Seeing your response, I see now that you are working with SQL Server. That makes things much better.
I'd recommend separating your SQL code into a separate class, away from the actual business class. Some might not agree with that, but it will keep the PURPOSE of the classes clear. (See Separation of Concerns.)
You want to have your business object handle the business logic, and a separate class that handles the work of getting data into and out of the database. That way, if you have a problem with the serialization logic, you have a far better idea of where to look, and your chances of hosing the business logic are greatly reduced. It also makes your application much easier to understand.
A little up front effort in writing a few more classes has a HUGE payoff down the road.
But that's just my opinion.
I prefer the idea of Mike Hofer, to have a Stored Proc in the SQL Server side to handle the actual data updates, and having a separate class to wrap calls to those stored procs.
Just my 0.02$
Not quite sure what the OP is asking.
You need to define exactly what you are doing in the "Save" method
If you are creating a new record in the Save method you need to use an INSERT statement.
If you are updating an existing record in the Save method then you need to use an UPDATE statement.
"Save" methods generally imply that both cases are handled by the procedure.
A better method would be to have ("Create" or "Insert") and ("Update" or "Save") methods.
Or perhaps have one procedure which handles both.