I'm currently pulling information using a query that I'm not allowed to tamper with:
Dim dt As DataTable = BLL.GetData(variable).Tables(0)
Immediately afterwards, I'm removing any records where a field begins with a specific value:
For Each dr As DataRow In dt.Rows
If dr.Item(2).ToString().StartsWith("value") Then
dr.Delete()
End If
Next
What I'd really like to do is something like:
dt.Select.Where(field1 => field1.StartsWith("value")).Delete()
I know that is not the syntax of it and I'm probably very off from what it would be like. The For Each works fine, I'm just trying to "simplify" it. Any idea? Any and all help is appreciated.
Actually, your initial code is probably the cleanest and most straight forward.
To delete items using LINQ, you first need to read them into a separate collection, then loop through that collection and call Delete on each record. If you'd rather go that route, you could try:
Dim records = dt.Rows.Where(Function(r) r.StartsWith("value")).ToList()
For Each r In records
r.Delete()
Next
The answer I think you are looking for is below from Microsoft. https://msdn.microsoft.com/en-us/library/det4aw50(v=vs.110).aspx?cs-save-lang=1&cs-lang=vb#code-snippet-2
Dim table As DataTable = DataSet1.Tables("Orders")
' Presuming the DataTable has a column named Date.
Dim expression As String
expression = "Date > #1/1/00#"
Dim foundRows() As DataRow
' Use the Select method to find all rows matching the filter.
foundRows = table.Select(expression)
Dim i As Integer
' Print column 0 of each returned row.
For i = 0 to foundRows.GetUpperBound(0)
Console.WriteLine(foundRows(i)(0))
Next i
Related
I have a DataTable containing about 30 rows and I need to extract all rows having a date field bigger than a date stored into a variable.
(This code will be executed a lot of times)
I found three ways to do this but I would like to know how to choose because I don't know the differences between various codes.
Here is what I was able to write (and my worries):
1st way (DataTable.Select)
Dim SelectedRows() As DataRow = DT_DBData.Select("In_Date=#" & _
LastDate.ToString("yyyy-MM-dd") & "#")
Using New_Dt As DataTable = SelectedRows.CopyToDataTable
'Some code
End Using
I'm worried about the string format: I'm afraid that some rows may be not extracted because of a date formatting error.
2nd way (query Linq)
Using New_Dt As DataTable = (From DBData In DT_DBData.AsEnumerable() _
Where DBData.Field(Of Date)("In_Date") >= LastDate).CopyToDataTable
'Some code
End Using
I never used Linq and so I don't know what kind of issues can it give me.
3rd way (For Each Loop + If Then)
Using New_Dt As DataTable = DT_DBData.Clone
For Each dr As DataRow In DT_DBData.Rows
If dr("In_Date") >= LastDate Then
New_Dt.Rows.Add(dr.ItemArray)
End If
Next
'Some code
End Using
I'm not really worried about this code. I only think that the others could be better or faster (but I can't answer to this)
Faster is kind of irrelevant when dealing with 30 rows.
The first one is kind of wasteful. You start with a DataTable, Select to get a subset, then convert the result into a new DataTable. Time to extract matching Rows: 8 ms.
You can work with the SelectedRows array without putting it into a new DataTable. If it goes back to the DB after "some code", I would not extract it from the DT.
By the way, there is no reason to worry about matching date formats as long as the DB column is a date type (and therefore, the DataTable column will be also). Dates do not have a format; formats are just how computers (and by extension, us) display them to users.
Dim drs = dt.Select(String.Format("StartDate > '{0}'", dtTgt.Date), "")
The date type I pass will compare/filter just fine with the DateTime data for that column. Formats only come into play when you convert them to string, which is mostly only needed for those pesky users.
One option you missed might be especially useful if this will be done over and over: A DataView:
dt.Load(cmd.ExecuteReader)
' create dataview
Dim dv As New DataView(dt)
dv.RowFilter = String.Format("StartDate > '{0}'", dtTgt.Date)
dv.Sort = "StartDate asc"
' show/iterate/whatever
dgv.DataSource = dv
If the data goes back to the DB, using this method, the rows will retain all the rowstate values.
I have a situation where I want to Insert into access DB table from MS SQL table.
Same columns and everything.
I have both data sets and both table adapter. I can do what ever I want inside each dataset - any manipulation but I cannot insert from one table to another.
I tried creating an Insert query for destination tableadapter but I cannot get the from working. Tried linking, nothing works.
Searched for days, simply cannot find it.
Thank you for your answer. Can you help me on my example. I'm having trouble setting this up. This is what i got:
Dim myToTableTableAdapter As FirstDataSetTableAdapters.ToTableTableAdapter
myToTableTableAdapter = New FirstDataSetTableAdapters.ToTableTableAdapter()
Dim myFromTableTableAdapter As SecondDataSetTableAdapters.FromTableTableAdapter
myFromTableTableAdapter = New SecondDataSetTableAdapters.FromTableTableAdapter()
myFromTableTableAdapter = myToTableTableAdapter.Clone
'but it doesnt work from here`
What I wanted to do is:
For each drfrom As DataRow In myFromTableTableAdapter.GetData
myToTableTableAdapter.InsertInto(drfrom.item(column01), drfrom.item(column02), drfrom.item(andSoOn))
Next
But it seem to me that this would take so much longer then a "Insert Into From Select" script.
You cannot insert a row from one table into another table, but there are a couple of ways to do what you want. One way (a little verbose) is this:
' sets it up with same schema but empty rows
mOutTable = inTable.Clone
' Now insert the rows:
For Each rowIn In inTable.Rows
r = mOutTable.NewRow()
For Each col In inTable.Columns
r(col.ColumnName) = rowIn(col.ColumnName)
Next
mOutTable.Rows.Add(r)
Next
mOutTable.AcceptChanges
A second way, which is more concise, is this:
outTable = inTable.Clone
For Each inRow As DataRow In inTable.Rows
outTable.LoadDataRow(inRow.ItemArray, False)
End If
outTable.AcceptChanges
Note that both inTable and outTable are ADO.NET DataTable objects. You cannot implement my suggestion on the DataAdapter objects. You must use the DataTable objects. Each DataTable can be associated with a DataAdapter in the standard fashion for ADO.NET:
Dim t as New DataTable()
a.Fill(t);
where a is the ADO.NET DataAdapter. I hope this helps!
Jim
I'm working with the following bit of code in VisualBasic.NET. It's essentially supposed to be pulling a row ID from the table with specific conditions in mind. However, I would like to set up a failsafe of getting around those conditions if need be.
I'm trying to write an If statement to compare the Item(0) against but this bit of code seems to trigger no matter what. How can I compare to see if the Query being written as QuestionConnectionQuery is actually returning rows?
For i As Integer = 1 To intNoOfQuestions
'TODO: If there are no valid questions, pull up any of them that meets the difficulty requirement....
' Go into the Database and retrieve a question that hasn't been selected in the last seven days.
Dim QuestionConnectionQuery As New OleDb.OleDbCommand("SELECT TOP 1 Questions.QuestionID, Questions.QuestionCategory & ' : ' & Questions.QuestionSubCategory AS Category FROM Questions WHERE (((Questions.QuestionDifficulty)=[?])) OR (((Questions.LastDateRevealed) Is Null)) OR ((Questions.LastDateRevealed)>=DateAdd('d',-7,Now())) ORDER BY Rnd(QuestionID);", QuestionConnection)
QuestionConnectionQuery.Parameters.AddWithValue("?", intQuestionDifficulty(i - 1).ToString)
Dim QuestionDataAdapter As New OleDb.OleDbDataAdapter(QuestionConnectionQuery)
Dim QuestionDataSet As New DataSet
QuestionDataAdapter.Fill(QuestionDataSet, "Questions")
' If the result is not null... add it to the array.
If IsNothing(QuestionDataSet.Tables("Questions").Rows(0).Item(0)) Then
' Add that to the intQuestArray() array
intQuestArray(i - 1) = QuestionDataSet.Tables("Questions").Rows(0).Item(0)
Else
MessageBox.Show("ERROR: Not enough questions.")
QuestionDataAdapter.Fill(QuestionDataSet, "Questions")
End If
' Update the database by adding today's date to the "LastDateRevealed" column of the table.
Dim QuestionUpdateQuery As New OleDb.OleDbCommand("UPDATE Questions SET LastDateRevealed=NOW() WHERE QuestionID = [?]", QuestionConnection)
QuestionUpdateQuery.Parameters.AddWithValue("?", QuestionDataSet.Tables("Questions").Rows(0).Item(0).ToString)
QuestionUpdateQuery.ExecuteNonQuery()
Next
If IsDBNull(QuestionDataSet.Tables("Questions").Rows(0).Item(0)) Then
https://msdn.microsoft.com/en-us/library/tckcces5(v=vs.90).aspx
For Each dr In ds.Tables(0).Rows
If String.IsNullOrEmpty(dr("BIL")) Then
dr.Delete() //how to delete this row?
End If
Next
first,will loop all data then check which row in BIL column are empty,if the row in BIL column are empty,then delete the row from dataset,how to delete this empty datarow?
Do you want to delete it in your database or do you want to remove it from the DataTable? Btw, use dr.IsNull("BIL") instead. Your code compiles only because you've set OPTION STRICT off because dr("BIL") returns object instead of string.
Dataset are getting data from EXCEL,so,dont have any identity
column.BTW i just want remove from datatable, not database
Then you have to use DataRowCollection.Remove instead of DataRow.Delete. With Delete wthe row will change it's RowState to Deleted. If you then use a DataAdapter to update the DataSet/DataTable or DataRow it will be deleted in the database.
But you can also use Linq-To-DataSet to filter the table and use DataRow.Field extension method which is strongly typed and supports nullable types:
Dim notNullBilRows = From row In ds.Tables(0)
Where Not String.IsNullOrEmpty(row.Field(Of String)("BIL"))
Now you can use CopyToDataTable to create a new DataTable with only rows where BIL is not null, which seems to be the actual requirement.
Dim tblNotNullBilRows = notNullBilRows.CopyToDataTable()
Here's the non-Linq approach with Remove, you have to create an intermediate collection since you cannot remove elements from a collection during enumeration:
Dim removeList = New List(Of DataRow)
For Each dr As DataRow In ds.Tables(0).Rows
If String.IsNullOrEmpty(dr.Field(Of String)("BIL")) Then
removeList.Add(dr)
End If
Next
For Each dr As DataRow In removeList
ds.Tables(0).Rows.Remove(dr)
Next
Try this:
For i As Integer = dt.Rows.Count - 1 To 0 Step -1
If String.IsNullOrEmpty(dt.Rows(i)("BIL")) Then
dt.Rows.RemoveAt(i)
End If
Next
You will want to put the index of the rows you wish to delete into an array, then iterate through the array deleting each rows from the datatable using the indexes. You will not need an 'identity' column to do this, the rows will automatically be asigned indexes.
Assuming you have 2 columns in table tbl: ColumnA and ColumnB
Dim dv as new DataView
dv = new DataView(tbl)
dv.RowFilter = "ColumnA <> '' AND ColumnB <> ''"
tbl = dv.ToTable()
tbl should no longer have empty rows. Hope this helps.
I made a datatable with 2 columns a transactionTime column and a numberOfTransactions column. I made the table with the pre-defined transaction times and want to add the number of transactions from an XML file. I have gotten through the XML file and want to add the data to the correct row. Here is the function:
Function AddRow(ByVal timeOfTransaction As String, ByVal numberOfTransactions As String, ByRef dataTableOfTransactions As DataTable) As String
Dim row() As DataRow = dataTableOfTransactions.Select("transactionTime = timeOfTransaction")
If row(0) IsNot Nothing Then
row(0)("numberOfTransactions") = numberOfTransactions
End If
Return Nothing
End Function
When I run this it overwrites the first element in the table's numberOfTransactions coloumn. I know it has to do with the "transactionTime = timeOfTransaction" part but I can't seem to get it to read timeOfTransaction as a reference to a string instead of a literal. Any help would be much appreciated. Thanks!
You need to write something like this :
Dim row() As DataRow = dataTableOfTransactions.Select("transactionTime=#" & timeOfTransaction & "#")
But be careful with your date/month or month/date format, it depends of your regional settings.
row(0)("numberOfTransactions") = numberOfTransactions
Right there you are telling the program to overwrite that value with number of transactions.
If you want that value you need to set it to something, not set something to it.
Also, if you want your select to work properly try doing it like this
dataTableOfTransactions.Select("transactionTime = " + timeOfTransaction)