This is the code:
Dim dr() As DataRow = DataSet.Tables("TableName").Select("EVENTNAME = '" & name & "'")
I get an "Object reference not set to an instance of an object." Error when this line is executed. It is looping through a list of selected items in a listbox. I think it has to do with how I have the datarow declared because I can look at the name and I see it ok and I also do a null check on the name before I use it.
Visual Studio 2008, VB.NET. Any ideas?
Yep it was a wrong table name. I guess after looking at the code for 8 hours that minor detail I just wasn't thinking to check. Thanks!
You probably have the wrong "TableName".
For me it looks like it is the select statement:
vm_DataTable_SELECT_string = "[MyField] = '" + vm_TEXT_string + "'";
DataRow[] o_DataRow_ARRAY_Found = vco_DataTable.Select (vm_DataTable_SELECT_string);
Related
Good eve guys.
I'm having a problem with my code.
The goal is, when I type a letter in the combobox, it wiill show a list of possible model names.
But whenever I type in that combobox, it gives me an error.
Here's the code I'm working on:
Private Sub cmbSearch_Change()
Dim conn As New ADODB.Connection
Dim record As New ADODB.Recordset
Dim model As String
model = cmbSearch.Text
If cmbSearch.Text <> "" Then
conn.Open "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" & App.Path & "\Database.mdb"
cmbSearch.Clear
record.Open "SELECT Model FROM LaptopSpecs WHERE Model LIKE '" & model & "%' ORDER BY Model", conn, 3, 3
If record.RecordCount > 0 Then
Do While Not record.EOF
cmbSearch.AddItem record.Fields("Model").Value
record.MoveNext
Loop
End If
cmbSearch.Text = model
End If
Set record = Nothing
Set conn = Nothing
End Sub
In the part conn.open, the error message pops up.
run-time error '-2147467259(80004005)': unspecified error
Assuming you are using Access:
This question isn't about Access, but if it where:
Expanding on this answer, I recommend removing all the code in your example, and replacing it with this (done in Form design mode):
Set the cmbSearch.RowSource property to a fixed query like:
SELECT Model FROM LaptopSpecs ORDER BY Model
Set the cmbSearch Auto Expand to True.
This will work for 98% of all ComboBox type-to-select scenarios, and should work for your example.
I have been searching for an answer on Stack Overflow and on Google but found nothing. I am doing this as a school project and can not get my head around it.
I'm am working with a Access Database and it will not allow me to search for the last name.
Here is my problem: Syntax error (missing operator) in query expression 'Last Name = '(Namethatwastypedwithoutbrackets)"
And this is my code
Private Sub cmdSearch_Click()
Dim sql As String
Call Conn.Connect
Adodc1.ConnectionString = Conn.connstr
Adodc1.CommandType = adCmdText
Adodc1.ConnectionString = connstr
sql = "Select * from Table1 where Last Name = '" & txtSearch.Text & "'"
Adodc1.RecordSource = sql
Adodc1.Refresh
End Sub
I really appreciate if anyone can tell me what's wrong since i don't have any idea what the error is.
The error message is telling you that you need brackets around your column name (Last Name) because it has spaces in it.
sql = "Select * from Table1 where [Last Name] = '" & txtSearch.Text & "'"
I have been trying to access the data returned from a dynamic linq query as an anonymous type. The advice I have found suggests that I should create a custom type and use it in the Select clause with the new keyword. I was directed to the followed Question for a code example:
System.LINQ.Dynamic: Select(" new (...)") into a List<T> (or any other enumerable collection of <T>)
This was indeed an excellent example which I incorporated into my code (which is VB so I had to do some translation).
My code compiles fine but When I run it , I get the error following error:
"Value cannot be null. Parameter name: member" at the following line from the example:
bindings[i] = Expression.Bind(type.GetProperty(properties[i].Name), expressions[i]);
This seems to be linked to expressions(i), which correctly contains two items as I am returning two fields from the database table. properties(i) holds the name of those two fields correctly. Any ideas as to what the value for member is supposed to be and where it should be found? Is it something from the database?
The where clause of this query works and when I run it as an anonymous type it brings back records (or rather two fields from records). The returned fields contain data not nulls.
Here is my VB version of the code from the example provided in the earlier Question. I have bolded or ** the line where the error occurs. Any ideas as to what is causing this?
Much appreciated.
Function ParseNew() As Expression
NextToken()
ValidateToken(TokenId.OpenParen, Res.OpenParenExpected)
NextToken()
Dim properties As New List(Of DynamicProperty)()
Dim expressions As New List(Of Expression)()
Do
Dim exprPos = tokenVal.pos
Dim expr = ParseExpression()
Dim propName As String
If TokenIdentifierIs("as") Then
NextToken()
propName = GetIdentifier()
NextToken()
Else
Dim [me] As MemberExpression = TryCast(expr, MemberExpression)
If [me] Is Nothing Then Throw ParseError(exprPos, Res.MissingAsClause)
propName = [me].Member.Name
End If
expressions.Add(expr)
properties.Add(New DynamicProperty(propName, expr.Type))
If tokenVal.id <> TokenId.Comma Then Exit Do
NextToken()
Loop
ValidateToken(TokenId.CloseParen, Res.CloseParenOrCommaExpected)
NextToken()
'CODE added to support strongly-typed returns
Dim type As Type = If(newResultType, DynamicExpression.CreateClass(properties))
Dim bindings(properties.Count - 1) As MemberBinding
For i As Integer = 0 To bindings.Length - 1
**bindings(i) = Expression.Bind(type.GetProperty(properties(i).Name), expressions(i))**
Next
Return Expression.MemberInit(Expression.[New](type), bindings)
End Function
I'm using the following LINQ to SQL compiled query.
private static Func<MyDataContext, int[], int> MainSearchQuery =
CompiledQuery.Compile((MyDataContext db, int[] online ) =>
(from u in db.Users where online.Contains(u.username)
select u));
I know it is not possible to use sequence input paramter for a compiled query and im getting “Parameters cannot be sequences” error when running it.
On another post here related , I saw that there is some solution but I couldn't understand it.
Does anyone know to use complied query with array as input paramter?
Please post example if you do.
Like the post that you referenced, it's not really possible out of the box. The post also references creating your own query provider, but it's a bit of overhead and complexity that you probably don't need.
You have a few options here:
Don't use a compiled query. Rather, have a method which will create a where clause from each item in the array resulting in something like this (psuedo-code):
where
online[0] == u.username ||
online[1] == u.username ||
...
online[n] == u.username
Note that you would have to use expression here to create each OR clause.
If you are using SQL Server 2008, create a scalar valued function which will take a table-valued parameter and a value to compare againt. It will return a bit (to indicate if the item is in the values in the table). Then expose that function through LINQ-to-SQL on your data context. From there, you should be able to create a CompiledQuery for that. Note that in this case, you should take an IEnumerable<string> (assuming username is of type string) instead of an array, just because you might have more than one way of representing a sequence of strings, and to SQL server for this operation, it won't matter what the order is.
One solution that I have found myself doing (for MS SQL 2005/2008). And I'm not sure if it is appropriate in all scenarios is to just write dynamic sql and execute it against the datacontext using the ExecuteQuery method.
For example, if I have an unbounded list that I am trying to pass to a query to do a contains...
' Mock a list of values
Dim ids as New List(of Integer)
ids.Add(1)
ids.Add(2)
' ....
ids.Add(1234)
Dim indivs = (From c In context.Individuals _
Where ids.Contains(c.Id) _
Select c).ToList
I would modify this query to create a SQL string to execute against the database directly like so...
Dim str As New Text.StringBuilder("")
Dim declareStmt as string = "declare #ids table (indivId int) " & vbcrlf)
For i As Integer = 0 To ids.Count - 1
str.Append("select " & ids(i).ToString() & " & vbcrlf)
If i < ids.Count Then
str.Append("union " & vbcrlf)
End If
Next
Dim selStatement As String = "select * From " & context.Mapping.GetTable(GetType(Individuals)).TableName & _
" indiv " & vbcrlf & _
" inner join #ids ids on indiv.id = ids.id"
Dim query = declareStmt & str.ToString & selStatement
Dim result = context.ExecuteQuery(of Individual)(query).ToList
So barring any syntax errors or bugs that I coded (the above is more or less psuedo code and not tested), the above will generate a table variable in SQL and execute an inner join against the desired table (Individuals in this example) and avoid the use of a "IN" statement.
Hope that helps someone out!
I am trying to extract the rss feed using linq. Thought it would be simple, but its is not returning any nodes. probably i have to go the channel/item node, but don't know how.
Dim rssUrl As String = "http://webclip.in/rss.aspx?u=mostliked"
Dim rssDoc As XDocument = XDocument.Load(rssUrl)
Dim rssResultSet = From node In rssDoc.Descendants("item") _
Select New With { _
.title = node.Element("title").Value, _
.link = node.Element("link").Value, _
.description = node.Element("description").Value, _
.pubDate = Date.Parse(node.Element("pubdate").Value) _
}
DataGridView1.DataSource = rssResultSet
Two issues here... First, you should correct this line:
.pubDate = Date.Parse(node.Element("pubDate").Value)
The pubDate is a case-sensitive node in XML. Secondly, your dataSource will never work because LINQ is lazy computation. You have to use ToList() or a similar method that enumerate your collection. If you debug within Visual Studio 2010, you'll see that rssResultSet does not have a value because it is only enumerated when your code calls for it. Replace with this:
DataGridView1.DataSource = rssResultSet.ToList()
My last piece of advice is to set your DataGrid to AutoGenerate it's columns.
the casing on pubdate is wrong. It should be "pubDate". otherwise, works fine.