I am trying to pass a query and existing datatable into a function. The function will query the passed datatable using the passed query and return the result.
Unfortunately, I am unable to return any data. I have posted my code below. Can anyone help me fix it? I don't know what I am doing wrong.
Public Function ExecQueryTest(Query As String, DT As DataTable) As DataTable
Dim Result() As DataRow
'initialize the table to have the same number of columns of the table that is passed into the function
Dim LocalTable As DataTable = DT
'initialize counting variables
Dim x, y As Integer
'use the select command to run a query and store the results in an array
Result = DT.Select(Query)
'remove all items from the localtable after initial formatting
For x = 0 To LocalTable.Rows.Count - 1
LocalTable.Rows.RemoveAt(0)
Next
'for loop to iterate for the amount of rows stored in result
For x = 0 To Result.GetUpperBound(0)
'add each array row into the table
LocalTable.Rows.Add(Result(x))
Next
ExecQueryTest = LocalTable
End Function
If there is a better way to accomplish my goal, I don't mind starting from scratch. I just want to be able to handle dynamic tables, queries, and be able to return the information in a datatable format.
The problem is here:
Dim LocalTable As DataTable = DT
That code does not do what you think it does. DataTable is a reference type, which means assigning DT to the LocalTable variable only assigns a reference to the same object. No new table is created, and nothing is copied. Therefore, this later code also clears out the original table:
'remove all items from the localtable after initial formatting
For x = 0 To LocalTable.Rows.Count - 1
LocalTable.Rows.RemoveAt(0)
Next
Try this instead:
Public Function ExecQueryTest(Query As String, DT As DataTable) As DataTable
ExecQueryTest = New DataTable() 'create new DataTable object to hold results
For Each row As DataRow In DT.Select(Query)
ExecQueryTest.LoadDataRow(row.ItemArray, True)
Next
End Function
Though you may also need to clone each DataRow record.
You can clear a table with just
LocalTable.Clear()
instead of using that cycle, Also the results of your select can be directly converted to datatable using
LocalTable = Result.CopyToDataTable
Related
I am trying to check if my dictionary contains values in my dataset.datatable and if its quantities in the second column of the dataset are less than or greater than the quantities in my datatable. I tried using the SELECT method but it doesn’t seem to work, I get the error BC30469 reference to non-shared member requires object reference?
I was just trying to do a simple search in the table first to see if I can even do that..... apparently not. Thanks for the help!
Dim row As DataRow = DataSet.DataTable.Select("ColumnName1 = 'value3'")
If Not row Is Nothing Then
searchedValue = row.Item("ColumnName2")
End If
You could get a dictionary to compare with the one you already have like this (assuming your key is a string and the amount an Int32 and that your dataset contains only one table):
Dim myDBDict As Dictionary(Of String, Int32) =
From e In myDataSet.Tables(0).Rows.Cast(Of DataRow).ToDictionary(Of String, Int32)(
Function(e) e.Field(Of String)("MyIDColumn"),
Function(e) e.Field(Of Int32)("myAmountColumn"))
after assign a row values of datatabe to a new data row object , any changes in this object affects on the data table , Why ?
have a look at this code.
DataRow dr = mydataset.Tables["NewTable"].Rows[0];
dr["Name"] = "hello";
Now if you try to debug your application you will find that the original data table ["NewTable"] has the new value hello instead of the old value Although we didn't return back the above data row to data table (we didn't save it )
I Just need a clarification and also need to know & understand what actually happen when i create an Object of a data row .
Both DataTable and DataRow are reference data types. This means that when you assign a variable to its reference in code, it simply holds a pointer back to the same memory location.
DataRow dr1 = mydataset.Tables["NewTable"].Rows[0];
DataRow dr2 = mydataset.Tables["NewTable"].Rows[0];
DataRow dr3 = dr1;
DataTable dt = mydataset.Tables["NewTable"];
DataRow dr4 = dt.Rows[0];
In the above example, dr1, dr2, dr3, and dr4 all point to the same memory location. Therefore if you edit dr4, the changes will appear on dr1, dr2, and dr3.
See Value Types and Reference Types for more information.
Simplest way how to loop and display through records using textbox, combo box and datetimepicker.
Below is a code but still cant figure it out
Dim dr As DataRow
Dim ds As Dataset
Dim dt As DataTable
<code to fill the dataset>
dt = ds.Tables(0)
For Each dr In dt.Rows
Console.WriteLine (dr("ColName"))
Next
ds.Dispose()
You need two loops to do this - an outer loop for the number of rows in the table, and an inner loop for the columns in each row.
You have the For Each for the rows already, but you need to know how many columns are in the DataRow, and print out the value in each column. You can get the count of columns from the DataTable.
Dim cols As Integer
cols = dt.Columns.Count - 1
For Each dr in dt.Rows
For i As Integer = 0 To cols
Console.WriteLine(dr(i).ToString())
Next
Next
Notice that I call ToString() on the value returned from each column, and reference the column by it's ordinal. When you access a specific column in the DataRow, it returns an Object, so you'll need to cast that value to the correct data type for use in your program.
The code you posted would have only printed the value for the column that had "ColName" as it's column name for each row. If you didn't have a column named "ColName" then you would see an error.
I am developing a program for a chain of restaurants, they should normally be able to calculate their guestcount and sales through a vb.net application with a connection to dbf files.
My dataset gets filled in correctly as is my datatable (checked by filling in datarowview = right data)
But then I get a problem, in all my functions using my datatable, the datatable skips the final value, in this case it is all values from a month so it either skips 31 or day 30.
Tried while, Tried for each, debugged alot (how i found it was the last value). But now I have no idea why the last value isn't used by the function
Public Function Getgctakeout(ByVal i_table As DataTable)
table = i_table
i = 0
gctakeout = 0
For Each row As DataRow In i_table.Rows
gctakeout = gctakeout + Convert.ToDouble(row(4))
Next row
'MessageBox.Show(gctakeout)
Return gctakeout
End Function
This function does not use the value of the last row to calculate gctakeout
what in the name of the lord is wrong :)
Assuming that your DataTable is really filled correctly, you have two other options to get the sum.
Use the old DataTable.Compute method which works also with .NET < 2.0
Use Linq-To-DatSet and it's Enumerable.Sum
1)
Dim Sum = CType(table.Compute("Sum(ColumnName)", Nothing), Double)
2)
Dim Sum = table.AsEnumerable().
Sum(Function(row)row.Field(Of Double)("ColumnName"))
I have a datatable that contains the rows of a database table. This table has a primary key formed by 2 columns.
The components are assigned this way: datatable -> bindingsource -> datagridview. What I want is to search a specific row (based on the primary key) to select it on the grid. I cant use the bindingsource.Find method because you only can use one column.
I have access to the datatable, so I do manually search on the datatable, but how can I get bindingsource row position based on the datatable row? Or there is another way to solve this?
Im using Visual Studio 2005, VB.NET.
I am attempting to add an answer for this 2-year old question. One way to solve this is by appending this code after the UpdateAll method(of SaveItem_Click):
Me.YourDataSet.Tables("YourTable").Rows(YourBindingSource.Position).Item("YourColumn") = "YourNewValue"
Then call another UpdateAll method.
Well, I end up iterating using bindingsource.List and bindingsource.Item. I didnt know but these properties contains the data of the datatable applying the filter and sorting.
Dim value1 As String = "Juan"
Dim value2 As String = "Perez"
For i As Integer = 0 To bsData.Count - 1
Dim row As DataRowView = bsData.Item(i)
If row("Column1") = value1 AndAlso row("Column2") = value2 Then
bsData.Position = i
Return
End If
Next