I am trying to learn some VB.NET for my coo-op that starts next week, and for that reason i took my portfolio web site that is on C# and just started to converting it to VB.NET to get familiar with the syntax.
I am sure my problem is simple however i have a hard time solving it.
I am trying to grab data with the linq query and then return it as list to bind to the Repeater.
I have the following function:
Public Function getProjects() As List(Of portfolio_website)
Using myPortfolio As New PortfolioDataContext
Try
Dim myProjects = (From p In myPortfolio.portfolio_websites _
Order By p.website_id Descending _
Select New With {.name = p.website_name, .id = p.website_id}).Take(5)
Return myProjects
Catch ex As Exception
Return Nothing
End Try
End Using
End Function
However I am getting an error.
If i would do it in C# then myProjects will be var and in return i will have
return myProjects.ToList();
And it would work fine. However if I try to use ToList() in VB.NET i am getting error that it cannot convert it from ling to sql List to the generic list.
How do i do this convertion in VB.NET ? or maybe there is another way ?
I am decent when it comes to C# however somewhat lost with the VB.NET syntax.
I hate it.
Second after I asked my question i realized my mystake.
It is same as in C#, but if i take
Select New With {.name = p.website_name, .id = p.website_id
then i either need to have a custom object, or i need to take everything.
So i changed my linq to sql to the
Dim myProjects = (From p In myPortfolio.portfolio_websites _
Order By p.website_id Descending _
Select p).Take(5)
Return myProjects.ToList()
and now everything is working.
Related
I have a datacontext that I'm trying to query, the results of which I want to bind to a gridview on a button click. Getting connected to the datacontext works great. I get the 1000s of records I expect. When I try to add the WHERE clause, I run into problems. Here's the button event I'm trying to make it happen at:
Protected Sub btnSearch_Click(ByVal sender As Object, ByVal e As System.EventArgs)
Dim dsource = New MY_DataContext().SV_XXXs '--- This works, the data is all there
gridRec.DataSource = dsource.ToList().Where(Function(dtable) dtable.PN = Session("PN")) '--- this fails
'--- Also tried this, it also did not work ----------------------------------------------------------
'--- gridRec.DataSource = dsource.Where(Function(dtable) dtable.PN = Session("PN")) '--- this fails
'----------------------------------------------------------------------------------------------------
gridRec.DataBind()
End Sub
The session variable is valid and the dsource is populating correctly, but I get the following error when it tries to execute the Where clause:
Evaluation of method
System.Linq.SystemCore_EnumerableDebugView`1[SV_REC].get_Items() calls
into native method System.WeakReference.get_Target(). Evaluation of
native methods in this context is not supported.
Also tried:
Dim results =
(
From T In dsource
Where T.PN = Session("SAFRReceiverPN")
Select T
).ToList
And get this error
Method 'System.Object CompareObjectEqual(System.Object, System.Object,
Boolean)' has no supported translation to SQL.
And tried:
Dim results = From t In dsource Where (t.PN = Session("SAFRReceiverPN")) Select t
nothing seems to work for me when trying a WHERE clause
C# or VB.NET are both cool if you have any suggestions.
Really, any help is appreciated, thanks.
LINQ to SQL doesn't know what to do when you try to access the session inside the query. Instead of doing that, fetch the value from the session before the query and store the result in a local variable, then use that local variable in your query. For example, in C#:
var receiver = (string) Session["SAFRReceiverPN"];
var results = dsource.Where(t => t.PN == receiver);
(I don't bother with query expressions when you're just trying to perform a simple filter.)
I have two values that have dates inside in the format dd/MM/yyyy and am trying to get the dates in between these two values. The values look like these(17/06/2013) in ONE and TWO variables. And then I send from my asp to an oracle procedure to execude a query and i get ORA-01843 not a valid month. Ive searched for this error but none of the solutions seemed to work for me. The thing is that this code used to work, I didnt change anything on these code and now it doesnt work for some reason.
Here is the code from my asp:
ONE = fromDate.Value
TWO = toDate.Value
Generic.searchBetweenDates(ONE, TWO, dt)
Public Function searchBetweenDates(ByVal PFROMDATE As String, ByVal PTODATE As String, ByRef PUSERINFO As DataTable)
Dim myDataTable As New DataTable
Dim myDataAdapter As New OracleDataAdapter
Dim oraCmd As New OracleCommand("cantine_test.searchbetweendates")
oraCmd.CommandType = System.Data.CommandType.StoredProcedure
oraCmd.Parameters.Add(New OracleParameter("PFROMDATE", OracleType.VarChar, 30)).Value = PFROMDATE
oraCmd.Parameters.Add(New OracleParameter("PTODATE", OracleType.VarChar, 300)).Value = PTODATE
oraCmd.Parameters.Add(New OracleParameter("PUSERINFO", OracleType.Cursor)).Direction = ParameterDirection.Output
Dim oConn As New OracleConnection(ConnectionString)
Try
oConn.Open()
oraCmd.Connection = oConn
cleanParams(oraCmd.Parameters)
myDataAdapter.SelectCommand = oraCmd
myDataAdapter.Fill(myDataTable)
If Not myDataTable Is Nothing Then
PUSERINFO = myDataTable 'return reference using byref param
End If
Catch ex As Exception
MsgBox(ex.Message)
Finally
oraCmd.Dispose()
oConn.Close()
myDataAdapter.Dispose()
End Try
Return PUSERINFO
End Function
And here is the code from my Oracle procedure:
PROCEDURE searchbetweendates
(PFROMDATE IN VARCHAR2, PTODATE IN VARCHAR2, PUSERINFO OUT SYS_REFCURSOR)
AS
BEGIN
OPEN PUSERINFO FOR
SELECT ORDERDATE,ORDERID,ORDERTIME,ORDERLIST,QUANTITY,ITEMPRICE,ORDERPRICE,LOCATION
FROM ORDERSDETAIL
WHERE ORDERDATE >= to_date(PFROMDATE, 'dd/MM/yyyy')
AND ORDERDATE <= to_date(PTODATE,'dd/MM/yyyy');
END;
Any ideas?
Oracle hurls ORA-01843 when we pass a string which doesn't match the specified date format: for instance when the string has the US format and the format mask doesn't:
SQL> select to_date('01/13/2013', 'dd/mm/yyyy') from dual
2 /
select to_date('01/13/2013', 'dd/mm/yyyy') from dual
*
ERROR at line 1:
ORA-01843: not a valid month
SQL>
So, the most likely explanation is that you are passing values which you think have a common format but in fact don't. This is fantastically common when "dates" are stored as strings. In other words, this is a debugging question.
Although, one thought occurs: is ORDERSDETAIL.ORDERDATE itself of a DATE datatype.
#6/17/2013#{Date} is the sort of string which will definitely lead to an ORA-1843 error. So you need to trace your code to discover where it comes from.
"how should i check if the value in my columns are correct"
Debugging dot Net is not my strong point. However, there are traditionally two ways. One is to step through the code in a debugging tool. If you're using Visual Studio or a similar IDE you should be able to do this. The other suggestion is to embed logging commands in your code and write trace messages e.g. to a file.
Which approach suits you best? Only you can tell.
I have a *.MDB database file, and I am wondering if it is possible or recommended to work against it using LINQ in C#. I am also wondering what some simple examples would look like.
I don't know a lot about LINQ, but my requirements for this task are pretty simple (I believe). The user will be passing me a file path to Microsoft Access MDB database and I would like to use LINQ to add rows to one of the tables within the database.
What you want is a LINQ to ODBC provider, or a LINQ to JET/OLEDB provider.
Out of the box, MS doesn't make one. There may be a 3rd party who does.
Actually I recently (today) discovered that you can access an Access database with LinqToSql. It must be in the 2002 or newer format, you will not be able to drag and drop the tables to your datacontext so either manually create the objects in your dbml or you can use SQL Server Migration for Access to move it to a sql server and then drag and drop all you want. When you want to actually create the context pass it an OleDbConnection. Use your standard Jet.OLEDB.4.0 connection string on the OleDbConnection and you are good to go. Not sure of the limitation this may incurr though. I just did a quick sample and did an OrderBy without issue.
I wrote a small sample program to test this out with David's answer. You'll need to make an access database and manually create the DBML for Linq-to-SQL, as you cannot drag 'n drop them.
Inserts fail, citing Missing semicolon (;) at end of SQL statement. but queries seem to work alright.
using System;
using System.Collections.Generic;
using System.Data.OleDb;
using System.IO;
using System.Linq;
using Linq2Access.Data;
namespace Linq2Access
{
class Program
{
static readonly string AppPath = Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location);
static readonly string DbPath = Path.Combine(AppPath, "Data", "database.accdb");
static readonly string DbConnString = #"Provider=Microsoft.ACE.OLEDB.12.0;Data Source='" + DbPath + "';Persist Security Info=False;";
static void Main(string[] args)
{
if (!File.Exists(DbPath))
throw new Exception("Database file does not exist!");
using (OleDbConnection connection = new OleDbConnection(DbConnString))
using (DataRepositoryDataContext db = new DataRepositoryDataContext(connection))
{
List<dbProject> projects = new List<dbProject>();
for (int i = 1; i <= 10; i++)
{
dbProject p = new dbProject() { Title = "Project #" + i };
for (int j = 1; j <= 10; j++)
{
dbTask t = new dbTask() { Title = "Task #" + (i * j) };
p.dbTasks.Add(t);
}
projects.Add(p);
}
try
{
//This will fail to submit
db.dbProjects.InsertAllOnSubmit(projects);
db.SubmitChanges();
Console.WriteLine("Write succeeded! {0} projects, {1} tasks inserted",
projects.Count,
projects.Sum(x => x.dbTasks.Count));
}
catch(Exception ex)
{
Console.WriteLine("Write FAILED. Details:");
Console.WriteLine(ex);
Console.WriteLine();
}
try
{
//However, if you create the items manually in Access they seem to query fine
var projectsFromDb = db.dbProjects.Where(x => x.Title.Contains("#1"))
.OrderBy(x => x.ProjectID)
.ToList();
Console.WriteLine("Query succeeded! {0} Projects, {1} Tasks",
projectsFromDb.Count,
projectsFromDb.Sum(x => x.dbTasks.Count));
}
catch (Exception ex)
{
Console.WriteLine("Query FAILED. Details:");
Console.WriteLine(ex);
Console.WriteLine();
}
Console.WriteLine();
Console.WriteLine("Press any key to continue...");
Console.ReadKey();
}
}
}
}
You can use a DataSet. There are linq extensions that will allow you to query the data with all that LINQ goodness we have become use to :)
eICATDataSet.ICSWSbuDataTable tbl = new eICATDataSet.ICSWSbuDataTable();
ICSWSbuTableAdapter ta = new ICSWSbuTableAdapter();
ta.Fill(tbl);
var res = tbl.Select(x => x.ProcedureDate.Year == 2010);
I have seen this question a lot and in several fora. I made a go at it and here is a complete answer for those who have been looking at it.
LinQ was not made for Access. However, many of the queries will work with Access, including delete procedure. So, according to me, there are only 2 crucial deficiencies when working with Access, which are:
not being able to save data.
not being able to drag and drop objects onto the dbml
Insert will fail with the error "missing semicolon (;)". This is because LinQ save procedure was made to save data and retrieve the primary key ID of the record saved in one go. We know that you cannot execute multiple SQL statements in Access, so that is the reason for that failure.
Update will fail with the error "record not found". An update procedure will of cause look for the record to be updated then update it. I cannot tell why it wouldn't find it, when normal LinQ query to find a record works fine.
Because there is so much benefit to use LinQ, I figured out how to work around the deficiency, while enjoy the other benefits throughout my application. This is how (NB: My codes are in VB.net, but you can convert if required):
Create the LinQ to SQL (.dbml) class to manage your LinQ against the access database, and a way to manager your save procedure. Below is the full procedures of what I created and I now work with LinQ to Access without any problems:
Add a DataGridView on a form. Add buttons for Add, Edit & Delete
Code to fill the grid:
Private Sub ResetForm()
Try
Using db As New AccessDataClassesDataContext(ACCCon)
Dim rows = (From row In db.AccountTypes
Where row.AccountTypeID > 1
Order By row.AccountTypeID Ascending
Select row).ToList()
Me.DataGridView1.DataSource = rows
End Using
Catch ex As Exception
MessageBox.Show("Error: " & vbCr & ex.ToString, "Data Error", MessageBoxButtons.OK)
End Try
End Sub
DetailForm
Code to set control values
Private Sub ResetForm()
Try
If _accountTypeID = 0 Then
Exit Sub
End If
Using db As New AccessDataClassesDataContext(ACCCon)
'Dim rows = (From row In db.AccountTypes
' Where row.AccountTypeID = _accountTypeID
' Order By row.AccountTypeID Ascending
' Select row.AccountTypeID, row.AccountType, row.LastUpdated).ToList()
Dim rows = (From row In db.AccountTypes
Where row.AccountTypeID = _accountTypeID
Select row).ToList()
For Each s In rows
Me.AccountTypeIDTextBox.Text = s.AccountTypeID
Me.myGuidTextBox.Text = s.myGuid
Me.AccountTypeTextBox.Text = s.AccountType
Me.AcHeadIDTextBox.Text = s.AcHeadID
Me.DescriptionTextBox.Text = s.Description
Me.LastUpdatedDateTimePicker.Value = s.LastUpdated
Next
End Using
Catch ex As Exception
End Try
End Sub
LinQToSQLClass
You will have to add the data objects to the dbml manually since you cannot drag and drop when using Access. Also note that you will have to set all the properties of the fields correctly in the properties windows. Several properties are not set when you add the fields.
Code to Save
Public Function SaveAccountType(Optional ByVal type As String =
"Close") As Boolean
Dim success As Boolean = False
Dim row As New AccountType
Using db As New AccessDataClassesDataContext(ACCCon)
If _accountTypeID > 0 Then
row = (From r In db.AccountTypes
Where r.AccountTypeID = _accountTypeID).ToList()(0)
If String.IsNullOrEmpty(row.AccountTypeID) Then
MessageBox.Show("Requested record not found", "Update Customer Error")
Return success
End If
End If
Try
With row
.myGuid = Me.myGuidTextBox.Text
.AccountType = Me.AccountTypeTextBox.Text
.Description = Me.DescriptionTextBox.Text
.AcHeadID = Me.AcHeadIDTextBox.Text
.LastUpdated = Date.Parse(Date.Now())
End With
If _accountTypeID = 0 Then db.AccountTypes.InsertOnSubmit(row)
db.SubmitChanges()
success = True
Catch ex As Exception
MessageBox.Show("Error saving to Customer: " & vbCr & ex.ToString, "Save Data Error")
End Try
End Using
Return success
End Function
Now replace these two lines:
If _accountTypeID = 0 Then db.AccountTypes.InsertOnSubmit(row)
db.SubmitChanges()
with something like this:
Dim cmd As IDbCommand
cmd = Me.Connection.CreateCommand()
cmd.Transaction = Me.Transaction
cmd.CommandText = query
If myGuid.Trim.Length < 36 Then myGuid = UCase(System.Guid.NewGuid.ToString())
cmd.Parameters.Add(New OleDbParameter("myGuid", row.myGuid))
cmd.Parameters.Add(New OleDbParameter("AccountType", row.AccountType))
cmd.Parameters.Add(New OleDbParameter("Description", row.Description))
cmd.Parameters.Add(New OleDbParameter("AcHeadID", row.AcHeadID))
cmd.Parameters.Add(New OleDbParameter("LastUpdated", Date.Now))
If AccountTypeID > 0 Then cmd.Parameters.Add(New OleDbParameter("AccountTypeID", row.AccountTypeID))
If Connection.State = ConnectionState.Closed Then Connection.Open()
result = cmd.ExecuteNonQuery()
cmd = Me.Connection.CreateCommand()
cmd.Transaction = Me.Transaction
cmd.CommandText = "SELECT ##IDENTITY"
result = Convert.ToInt32(cmd.ExecuteScalar())
The last part of the code above is what gets you the ID of the record saved. Personally, I usually make that an option, because I don't need it in most of the cases, so I don't need to add that overhead of fetching back data every time a record is saved, I am happy just to know a record was saved.
That is the overhead added to LinQ, which causes Insert to fail with Access. Is it really necessary to have it? I don't think so.
You may have noted that I normally put my Update and Insert procedures together, so that saves me time and has address both the Insert & Update procedures in one go.
Code for Delete:
Private Sub DelButton_Click(sender As Object, e As EventArgs) Handles DelButton.Click
Using db As New AccessDataClassesDataContext(ACCCon)
Dim AccountTypeID As Integer = Me.DataGridView1.CurrentRow.Cells(0).Value
Dim row = From r In db.AccountTypes Where r.AccountTypeID = AccountTypeID
For Each detail In row
db.AccountTypes.DeleteOnSubmit(detail)
Next
Try
db.SubmitChanges()
Catch ex As Exception
' Provide for exceptions.
MsgBox(ex)
End Try
End Using
End Sub
Now you can enjoy LinQ to Access! Happy coding :)
LINQ to SQL only works for SQL Server databases. What you need is the Microsoft Entity Framework. This makes object oriented access to your mdb. From this you can run LINQ queries.
http://msdn.microsoft.com/en-us/library/aa697427(vs.80).aspx
When I write a code like below, I take this error message: "The query operator 'ElementAtOrDefault' is not supported."
How can I fix it?
Dim tmpQuestion As New UIData
Dim strViews = From t In tmpQuestion.LU_QUESTIONs _
Where t.ID_QUESTION = Request.QueryString("IdQuestion") _
Select t
Dim mtViews = strViews(0).MT_VIEWS
You haven't really queried yet.
strViews isn't the result set, it is the query. You need to actually retrieve some data.
var chosen = strViews.FirstOrDefault();
Have you tried using the FirstOrDefault() then check to make sure it is not null. My VB syntax is probably suspect, but you get the idea.
Dim strView = (From t In tmpQuestion.LU_QUESTIONS _
Where t.ID_QUESTION = Request.QueryString("IdQuestion") _
Select t).FirstOrDefault()
Dim mtViews as ...
If Not strView Is Nothing
mtViews = strView.MT_VIEWS
EndIf
I am no expert in VB or LINQ2SQL but does this not have anything to do with the fact that you say strViews(0).MT_VIEWS while there is a chance that strViews can be null?
"Both DataSource and DataSourceID are defined on 'grdCommunication'. Remove one definition."
I just got this error today, the code has been working until this afternoon I published the latest version to our server and it broke with that error both locally and on the server. I don't use "DataSourceID", the application reads database queries into a datatable and sets the datatable as the DataSource on the GridViews. I did a search in Visual Studio, searching the entire solution and the string "DataSourceID" does not appear in even 1 line of code in the entire solution. This is the first thing that freaked me out.
I figure it had been working yesterday, so I reverted the code to yesterday's build. The error was still there. I kept going back a build, and still the issue is there. I went back a month, I am still getting the same error. This application was working fine this morning? There has really been no code changes, and no where in the application is the DataSourceID EVER set on any of the gridviews. Has anyone ever seen anything like this at all??
How can I get that error if DataSourceID is never set... and the word "DataSourceID" is not in my solution? I just did a wingrep on the entire tree doing a case insensitive search on datasourceid.... pulled up absolutely nothing. That word is absolutely no where in the entire application.
<asp:GridView ID="grdCommunication" runat="server"
Height="130px" Width="100%"
AllowPaging="true" >
... standard grid view column setup here...
</asp:GridView>
// Code behind.. to set the datasource
DataSet dsActivity = objCompany.GetActivityDetails();
grdCommunication.DataSource = dsActivity;
grdCommunication.DataBind();
// Updated: removed some confusing notes.
Try this:
DataSet dsActivity = objCompany.GetActivityDetails();
grdCommunication.DataSource = dsActivity.Tables[0];
grdCommunication.DataBind();
Holy smoke batman. The Table name was changed causing my Datasource to be no good. But that error message doesn't make any sense in this situation. So technically tsilb's solution will work if I call the table by index instead of by name, so I'll mark his solution as correct.
After reading his post, I tried dsActivity.Tables["Activities"] instead of passing the dataset to the Datasource and the table name to the Datamember, and obviously that didn't work, but If I pass the actual index, which I don't like doing because that index might change, then it is now working. But the messed up part, was that error.. That error was completely off base as to what the problem was. saying that I defined both and to remove one, when in reality, that was not the case. and another really messed up thing, was the table name was only changed to be all upper case... But hey, "Activities" is a different key than "ACTIVITIES".
Replace this code before this grdCommunication.DataSource = dsActivity;
grdCommunication.DataBind();
grdCommunication.DataSourceID="";
tslib is right, don't do:
grdCommunication.DataSourceID = null;
or the string.Empty version. You only use the DataSourceID if you're using a SqlDataSource or ObjectDataSource control for your binding.
It's called "declarative" binding because you're using "declared" controls from on your page. Binding to controls does not require a call to the DataBind() method.
Because you're DataBinding manually (calling grd.DataBind()) you only set the DataSourrce and then call DataBind().
I ran into the same error, but a totally different problem and solution. In my case, I'm using LINQ to SQL to populate some dropdown lists, then caching the results for further page views. Everything would load fine with a clear cache, and then would error out on subsequent page views.
if (Cache["countries"] != null)
{
lbCountries.Items.Clear();
lbCountries.DataValueField = "Code";
lbCountries.DataTextField = "Name";
lbCountries.DataSource = (Cache["countries"]);
lbCountries.DataBind();}
else
{
var lstCountries = from Countries in db_read.Countries orderby Countries.Name select Countries;
lbCountries.Items.Clear();
lbCountries.DataValueField = "Code";
lbCountries.DataTextField = "Name";
lbCountries.DataSource = lstCountries.ToList();
lbCountries.DataBind();
Cache.Add("countries", lstCountries, null, System.Web.Caching.Cache.NoAbsoluteExpiration, new TimeSpan(0, 240, 0), System.Web.Caching.CacheItemPriority.High, null);
}
The issue came from:
Cache.Add("countries", lstCountries, null, System.Web.Caching.Cache.NoAbsoluteExpiration, new TimeSpan(0, 240, 0), System.Web.Caching.CacheItemPriority.High, null);
When it should have been:
Cache.Add("countries", lstCountries.ToList(), null, System.Web.Caching.Cache.NoAbsoluteExpiration, new TimeSpan(0, 240, 0), System.Web.Caching.CacheItemPriority.High, null);
I got this error today, turns out that it had nothing to do with DataSourceID, and had everything to do with the DatasSource itself.
I had a problem in my DatasSource , and instead of getting a DatasSource related error, I got this meaningless error.
Make sure you're DatasSource is good, and this error should go away.
always bind dataset with table index to gridview...
ex. gridgrdCommunication.Table[0]; as metioned above by Tsilb
second way you intentionally write..
gridgrdCommunication.DataSourceID = String.Empty;
gridgrdCommunication.DataSource=ds;
gridgrdCommunication.DataBind();
Check you database structure.... if you are acceding your data throw a dbml file, the table structure in your database it's different of the dbml file structure
If you are using the Object Data Source and want to conditionally reload the grid in code behind you can successfully do this:
Dim datatable As DataTable = dataset.Tables(0)
Dim dataSourceID As String = gvImageFiles.DataSourceID
gvImageFiles.DataSourceID = Nothing
gvImageFiles.DataSource = datatable.DefaultView
gvImageFiles.DataBind()
gvImageFiles.DataSource = Nothing
gvImageFiles.DataSourceID = dataSourceID
You need to chose one way to bind the grid
if it is from code behind means using c# code then remove the datasourceid property from grid view from design view of grid
like this
//you have to make it like this
Please try this:
gvCustomerInvoiceList.DataSourceID = "";
gvCustomerInvoiceList.DataSource = ci_data;
gvCustomerInvoiceList.DataBind();
I got this error today. It turns out that my stored procedure did not return neither any record nor a structure. This was because I had an empty try catch without a raiserror.
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Page.DataBind()
End Sub
Function GetData()
Dim dt As New DataTable
Try
dt.Columns.Add("ROOM_ID", GetType(String))
dt.Columns.Add("SCHED_ID", GetType(String))
dt.Columns.Add("TIME_START", GetType(Date))
dt.Columns.Add("TIME_END", GetType(Date))
Dim dr As DataRow = dt.NewRow
dr("ROOM_ID") = "Indocin"
dr("SCHED_ID") = "David"
dr("TIME_START") = "2018-01-03 09:00:00.000"
dr("TIME_END") = "2018-01-03 12:00:00.000"
dt.Rows.Add(dr)
Catch ex As Exception
MsgBox(ex.ToString)
End Try
Return dt
End Function
and add this to your item DataSource="<%# GetData() %>"
In my case the connection string to the database was not working. Fixing the connection string got rid of this error.