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)
Related
So I have an application in VB.net that is pulling data from a table and inserting it into an arraylist to be used later. What I want to do is before adding the object to the arraylist, I want to check that arraylist to see if the object exists, but I want to be able to check based off a particular property of that object.
Here is an example of what I am talking about:
Lets say Im pulling info from a table with the following columns:
InvoiceNo|DateCharged|Quantity|TotalCharge
I have a SQL statement that pulls info from a table and then I use a data reader to go through the info. My Code looks somewhat like this:
Dim dbobjM As New clsDbobjManual()
If dbobjM.Exec_SQL_DR("SELECT InvoiceNo, DateCharged, Quantity, TotalCharges From Invoices") = 0 Then
If dbobjM.DataReader.HasRows Then
Dim invoicelist As New ArrayList(5000)
Dim invoiceno As String = String.Empty
Do While dbobjM.DataReader.Read()
invoicelist.Add(New Invoice(dbobjM.DataReader.GetInt32(0), dbobjM.DataReader.Value(1), dbobjM.DataReader.GetInt32(2), dbobjM.DataReader.GetFloat(3)))
Loop
End If
End if
(Exec_SQL_DR is a function in the clsDbobjManual class that check to make sure the SQL is in the proper syntax first and checks that records are returned otherwise it returns an error)
Basically what I want to do is before I add a new object to the arraylist I want to check if an object already exists in the list where the InvoiceNo is a particular value, or the value pulled from the table each time to make sure there is no duplicates. I want one object in the list for each InvoiceNo.
Im looking for something like:
If Not invoicelist.Contains(Object where InvoiceNo = dbobjM.DataReader.GetInt32(0)) Then
invoicelist.Add
End If
But I cant seem to find what I need, any help is greatly appreciated
There is no need to use the outdated ArrayList: a List will serve you better. Please see ArrayList vs List<> in C# if you need reasons - the advantages for a list apply to VB.NET too.
Without seeing your clsDbobjManual or Invoice classes, I ended up writing the minimal code to do what you're after, which is basically the check for invoices.Any(Function(i) i.InvoiceNo = inv.InvoiceNo), which you can do if you have the data in a List(Of Invoice).
Please note that I assumed that the appropriate data types have been used in the database - you should use the Decimal type for money as otherwise you can end up with significant rounding errors, and a date should be stored as DateTime, not as a string.
Imports System.Data.SqlClient
Module Module1
Class Invoice
Property InvoiceNo As Integer
Property DateCharged As DateTime
Property Quantity As Integer
Property TotalCharges As Decimal
Sub New()
' empty constructor
End Sub
Sub New(invoiceNo As Integer, dateCharged As DateTime, quantity As Integer, totalCharges As Decimal)
Me.InvoiceNo = invoiceNo
Me.DateCharged = dateCharged
Me.Quantity = quantity
Me.TotalCharges = totalCharges
End Sub
End Class
Function LoadData() As List(Of Invoice)
Dim invoices As New List(Of Invoice)
Dim connStr As String = "your connection string"
Dim sql = "SELECT InvoiceNo, DateCharged, Quantity, TotalCharges From Invoices"
Using sqlConn As New SqlConnection(connStr)
Using sqlCmd As New SqlCommand(sql, sqlConn)
Dim reader As SqlDataReader = sqlCmd.ExecuteReader()
While reader.Read()
Dim inv As New Invoice(reader.GetInt32(0), reader.GetDateTime(1), reader.GetInt32(2), reader.GetDecimal(3))
If Not (invoices.Any(Function(i) i.InvoiceNo = inv.InvoiceNo)) Then
invoices.Add(inv)
Else
' there is a duplicate invoice number
End If
End While
End Using
End Using
Return invoices
End Function
Sub Main()
Dim uniqueInvoices As List(Of Invoice) = LoadData()
' uniqueInvoices now contains the data
End Sub
End Module
If you had a lot of invoice entries to go through, you would likely be better off writing an SQL query to do that.
If you actually just want to find duplicate invoice numbers, you could use the SQL
SELECT [InvoiceNo]
FROM testTable
GROUP BY [InvoiceNo]
HAVING COUNT([InvoiceNo]) > 1
Finally, please ensure that you are using Option Strict On so that you don't make accidental data type errors - they can drastically slow down your program and lead to erroneous results.
You can use linq to select the objects that matches your condition.
Dim result = (From invoiceitem As Invoice
In invoicelist
Where invoiceitem.InvoiceNo = dbobjM.DataReader.GetInt32(0)
Select invoiceitem).ToList()
If Not result.Count > 0 Then
invoicelist.Add(New Invoice(dbobjM.DataReader.GetInt32(0), dbobjM.DataReader.Value(1), dbobjM.DataReader.GetInt32(2), dbobjM.DataReader.GetFloat(3)))
End If
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.
This is the code that tries to grab the largest StockID from the database (Access database) , but my problem is that it generates StockID's up to "S10", after this it simply doesn't increment any further. This is the subroutine that generates the StockID:
Sub generate_Stock_ID()
Dim Stock_start As String = "S"
Dim Stock_Gen As String = "SELECT MAX(StockID) FROM tblStock WHERE StockID LIKE '" & Stock_start & "%%%' "
Dim da As OleDbDataAdapter = New OleDbDataAdapter(Stock_Gen, conn)
Dim ds As DataSet = New DataSet
da.Fill(ds, "StockID")
Dim dt As DataTable = ds.Tables("StockID")
Dim count As Integer = ds.Tables("StockID").Rows.Count
If ds.Tables("StockID").rows.count = 0 Then
StockID = "S1"
Else
StockID = ds.Tables("StockID").Rows(0).Item(0)
StockID = StockID.Substring(1, (StockID.Length - 1))
StockID = Stock_start & (StockID + 1)
End If
End Sub
Screenshot of my database
Note* there are multiple ID's for various other subroutines which all share the same incrementation issue, so if i fix this i fix the other ones too. So at the moment i think my problem lies in the syntax of my SQL statement, but im open to suggestions.
Thanks!
Don't treat an Integer as String. Otherwese MAX or ORDER BY will use lexicographical instead of numerical order which means that S11 is "lower" than S2.
So you should make this column an int-column and prepend S only where you display it. Then MAX(StockID) returns an Integer, you just have to cast it and add 1:
Using conn As New OleDbConnection("Connection-String")
Using cmd As New OleDbCommand(Stock_Gen, conn)
conn.Open()
Dim stockIDObj As Object = cmd.ExecuteScalar()
If stockIDObj IsNot Nothing Then
Dim maxStockId As Int32 = DirectCast(stockIDObj, Int32)
maxStockId += 1
' ...... '
End If
End Using
End Using
You should also change OPTION STRICT to ON. Then this would never compile since the same variable cannot be used for an Object, String and Integer which is very good since it prevents errors.
If you want to keep it as string you have to cast the substring always in the database which is less readable and less efficient. I also don't know how to do it in access.
If you want to change the type of column in an already populated table you should first add a new column with a similar name which is of type int. If all have S at the beginning you could first remove that, then you can update the new column with the casted int value. Finally you can delete the old column and rename the new to the old.
The root of this issue that StockID is a STRING and 'S1'>'S10' so for all StockId > 10 you get max = 'S1'.
As a fast fix try to change MAX(StockID) to:
SELECT 'S'+CAST(MAX(CAST(SUBSTRING(StockID,2,100) as int)) as varchar(100))
For ACCESS DB try to use:
SELECT "S" & cstr(MAX(CINT(MID(StockID,2,100))))
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
I'm trying to query old Access database tables and compare them with SQL Server tables.
They often don't have primary keys, or they have extra fields that had some purpose in the nineties, etc., or the new tables have new fields, etc.
I need to find records - based on a set of fields specified at runtime - that are in one table but not another.
So, I do this kind of query all the time in SQL, when I'm comparing data in different tables:
dim fields_i_care_about as string = "field1, field2, field3"
'This kind of thing gets set by a caller, can be any number of fields, depends on the
'table
dim s as string= ""
dim flds = fields_i_care_about.split(",")
for i as integer = 0 to ubound(flds)
if s > "" then s += " AND "
s += " dysfunctional_database_table." & flds(i) & "=current_database_table." & flds(i)
next
s = "SELECT * from dysfunctional_database_table where not exists (SELECT * from current_database_table WHERE " & s & ")"
====
I'm trying to do this using Linq because it seems like some of the datatype problems with two different database types become less of a headache,
but I'm new to Linq and totally stuck.
I got as far as this:
Put old and new tables into datatables as dt1 and dt2
Dim new_records = _
From new_recs In dt2.AsEnumerable
Where Not ( _
From old_recs In dt1.AsEnumerable Where old_recs(field1) = new_recs(field1) AndAlso old_recs(field2) = new_recs(field2)).Any
Select new_recs
But I can't figure out how to put this part in on the fly -
old_recs(field1) = new_recs(field1) AndAlso old_recs(field2) = new_recs(field2)
So far I've tried:
putting the fields I want to compare and making them a string and just putting that string in as a variable ( I thought I was probably cheating, and I guess I was)
dim str = old_recs(field1) = new_recs(field1) AndAlso old_recs(field2) = new_recs(field2)
From new_recs In dt2.AsEnumerable
Where Not ( _
From old_recs In dt1.AsEnumerable Where str).Any
Select new_recs
It tells me it can't convert a Boolean -
Is there any way to do this without Linq expressions? They seem far more complex than what I'm trying to do here, and they take a lot of code, and also I can't seem to find examples of Expressions where we're comparing two fields in a subquery.
Is there a simpler way? I know I could do the usual EXISTS query using JOIN or IN - in this case I don't need the query to be super fast or anything. And I don't need to use a DataTable or DataSet - I can put the data in some other kind of object.
So I found a lot of sample code that used MethodInfo and reflection and things like that, but I couldn't get any of it to work - these Datarows have a Field method but it requires that you add an (of object) argument before the field name argument and that's tricky to do.
So I'm not sure if this solution is the most efficient way, but at least it works. I'd be interested in finding out whether this way of doing it is efficient and why or why not. It seemed like most people used reflection to do this kind of thing, but I couldn't get that working properly and anyway what I'm trying to do is pretty simple while those methods were pretty complex. I suppose I'm doing Linq with a SQL mindset, but anyway it works.
Dim f As Func(Of DataRow, DataRow, String, Boolean) = Function(d1 As DataRow, d2 As DataRow, s As String)
Dim fields = Split(s, ",")
Dim results As Boolean = True
For k As Integer = 0 To UBound(fields)
Dim obj = DataRowExtensions.Field(Of Object)(d1, fields(k))
Dim obj2 = DataRowExtensions.Field(Of Object)(d2, fields(k))
If obj <> obj2 Then results = False : Exit For
Next
Return results
End Function
Dim new_records = _
From new_recs In dt2.AsEnumerable.AsQueryable()
Where Not ( _
From old_recs In dt1.AsEnumerable.AsQueryable Where f(old_recs, new_recs, id_key)).Any
Select new_recs
Try
Return new_records.CopyToDataTable
Catch ex As Exception
Stop
End Try