When I query a DataTable using LINQ, are the rows returned as references? Either way, is it possible to control this behaviour, so that rows are either returned as references or as new rows?My guess is that all objects are returned as references by default, since that seems to be the normal behaviour in most programming languages.
View 2 RepliesI am currently writing unit tests for an application near completion (before management looks at it and turns it inside out). I am testing the business layer and a method is set to return a datatable of all "GroupID"s, which are simply an integer to represent the group that a user belongs to.
I'm assuming the best way to assert on this unit test would be to assert that the correct groupIDs are being returned from a controlled test database. However, I'm not sure how to assert on a datatable. Is the only (and best) possible way to accomplish this to simply loop through the datatable until it's empty and add each value to an array of integers? How would one go about asserting on this test?
there is two datatable at some datasetsone of them is tbl1 and fileds is (pcode,points) other table is tbl2 and fields is (pcode,stoped)"pcode" is equal at two tables
View 6 RepliesUsing the following DataTable:
Dim d As New DataTable()
d.Columns.Add("Product", GetType(System.String))
d.Columns.Add("Value", GetType(System.Double))
[code]....
I'm trying to use LINQ to identify if there are more than one of any type of product. In SQL, this would work something like:
SELECT Product FROM SOME_TABLE HAVING COUNT(*) > 1
I can't for the life of me work out how to do this in LINQ. I was following someone who did something like this:
Dim q = From row In d.AsEnumerable()
Group row By New { column1 = row("Product"), column2 = row("Value") }
Into grp
[code]....
But I get an error when I try to actually use 'q'. how I can make this work?
I am trying to get distinct rows based on multiple columns (attribute1_name, attribute2_name) and get datarows from datatable using Linq-to-Dataset.[code]How to do thin Linq-to-dataset?
View 3 RepliesI have three sub tables that I want to process. For each I want to combine the rows, as they are only different by contents in the second column(I want to do the same to the fourth column, later):
'Sub table 1
xx|C201 |02300877 |Samsung |....
xx|C201 |02300877 |Toshiba |....
xx|C213 |02300877 |Samsung
[code]....
p.s. For the fourth column, Manufacturer information , I want to do the same and I'd probably get something like this for the final table:
xx| C201,C213,C606,C619 |02300877 | Samsung
xx| C201,C213,C606,C619 |02300877 | Toshiba
xx| C303, C305,C712 |02301163
xx| C207, C209, C708 |02301165
I have a datatable as shown in the figure. Let me explain my required based on this image. I have 7 rows of data. The rows 1 and 2 contains columns till UnitSqcNo same. I want only row 3 among the two. In general I want select all the rows with distinct model, unittype, unit and rest with greater CompId. ie the table should look like
View 1 RepliesI am trying to distinct on multiple columns and get datarows from datatable. but getting error.
Dim query As IEnumerable(Of DataRow) =
(From row As DataRow In SourceTable.AsEnumerable() _
Select row.Field(Of String)("ColumnName1"),
[Code]....
I want another datatable with distinct row based on given columns from SourceTable.
I'm trying to query a DataTable to get a collection of rows but I'm finding that my search string has to be the exact length of the columns width. So, for example this won't work:
Dim rows As DataRow() = (From r In myTable.AsEnumerable() Where r.Field(Of String)("fname") = "Bob").ToArray()
...but this will:
Dim rows As DataRow() = (From r In myTable.AsEnumerable() Where r.Field(Of String)("fname") = "Bob ").ToArray()
The search term ("Bob") has to be padded with spaces to make it equal in length to the column width (10 characters). Is this how it's supposed to work or am I doing something wrong?Also, how can I do a LIKE search? So for example, I want to search for all names that start with "Bo" or whatever. ie. "Bo*".
I'm populating a datatable with this
Using con As New MySqlConnection(strCon)
'get users direct friends
Dim cmd As MySqlCommand = New MySqlCommand("SELECT distinct f.* FROM friends f WHERE (f.UserID = ?UserID) AND (f.FriendUserID <> ?FriendUserID)", con)
cmd.Parameters.AddWithValue("?UserID", UserID)
[Code]...
now I need to create another command, datatable and datareader in this same function and add the rows of that datatable to the one above. What is the most efficient way of doing this?
I want to delete the rows of a DATABLE that verify a criterion. Someone would be so kind to show me how do this.For example, I have a DataTable with "customers" and I want to delete customers who live in "Madrid"... criterion: CityCustomer='Madri
View 10 RepliesI have a Datatable with one column of the table being 'PartNum(product part number)'. I used EntriesTable.DefaultView.Sort = "PartNum ASC" to sort the whole Table, with respect to the information in this column. Now I'm just trying to further sort the table by grouping rows that have same info under that column together and do something to each of such groups. but I'm kinda stuck here.
I'm thinking of creating some sub-DataTables out of the original one and have these sub-tables to hold those rows with same info under "PartNum". Does anyone have ideas how to do that? maybe with DataReader or DataView ,
I am wondering if it is possible to filter data from a datatable.Sample datatable
Quote:
Sno CatID Nos
1 XYZ 25
[code].....
I have a model that returns a dataset to a view and builds a list. The crazy thing is that I have tested this code with IE, Safari on Mac and Windows, Chrome and Opera and all return data. However, on the iPad or iPhone, zero rows are returned from the dataset object. It seems that the model is in fact passing the dataset to the view. I am using jquerymobile to render the view for the iOS devices and have taken that out of the mix to test and it still doesn't work.
[Code]...
I'd like to know after I've executed MySqlReder = MySqlCommand.ExecuteReader() how many rows it returned. If it's one I can continue processing with the data. If it's more than one I need to populate a drop down list box.
View 6 RepliesAfter connecting to a database using DataReader, how can I count the number of rows ?
View 2 RepliesI have a DLL that is written in C++. the functions of the DLL have parameters defined as unsigned char:
apiStatus __declspec(dllexport) __stdcall Gen2Read(HANDLE
hCom,unsigned char Membank,unsigned char WordPtr,unsigned char WordCnt, unsigned char *value, unsigned char ReaderAddr );
I have tried
<DllImport("Mr915ApiV10.dll", CharSet:=CharSet.Auto)> _
Public Function Gen2Read(ByVal hComHandle As IntPtr, ByVal Membank As Byte, ByVal WordPtr As Byte, ByVal WordCnt As Byte, ByRef value As IntPtr, ByVal ReaderAddr As Byte) As Integer
End Function
And the call:
Gen2Read(hComHandle, membank, wordptr, wordcnt, value, m_ReaderAddres)
In the original code in c + + value is: unsigned char buf [40]. And I'm not able to convert the value returned by reference into Byte ().
This should be a fairly common question, but I haven't found a straightforward answer anywhere.
If I instantiate an object within a function in VB.NET and return it, does it return it be reference or by value. IE - should I be worried about performance if I write something like this:
Public Function ret_obj_func() As big_object
Dim ret_obj As New big_obj(<lots of stuff>)
Return ret_obj
End Function
If I call this function from somewhere else, will it instantiate the object in the ret_obj and then create a deep copy to pass back a copy to the caller, Or will it just pass back a reference?
Dim _tableBackLogs As System.Data.DataTable
Do While i - 2 > 0
_tableBackLogs = Global.DataAccess.GetDataTable("SELECT SubjectID,SubjectName,Grade FROM SubjectPI WHERE RegNo='" & CInt(HttpContext.Current.Session("userName")) & "' AND Status='Fail' AND Semester='" & i - 2 & "'")
i = i - 2
Doing this replaces the previous data in the DataTable. I want to retain the previous data i.e i want the new rows to be added to the DataTable w/o replacing the previous rows.
If I instantiate an object within a function in VB.NET and return it, does it return it be reference or by value. IE - should I be worried about performance if I write something like this:
Public Function ret_obj_func() As big_object
Dim ret_obj As New big_obj(<lots of stuff>)
Return ret_obj
End Function
If I call this function from somewhere else, will it instantiate the object in the ret_obj and then create a deep copy to pass back a copy to the caller, Or will it just pass back a reference?
Dim query = (From p in Parent _
select _
p.ID, _
Tags = String.Join("|", p.Child.Select(Function(c) c.Tag.TagName).ToArray)).Take(100)
In the above query, when using Take to limit the rows returned, a separate SQL query is executed for each row to return the 'Tags' field. If I remove Take(100), a single query to sent to Sql Server.So, how do I limit the number of rows returned, while preventing a new sub query being executed for each row?
Have seen some solutions for C# but do not know how to solve the issue in VB.NET.
Query:
Dim Query = (From t In myEntities.Bookings
Where(t.Ref = Someid)
Select t.People).Sum()
t.Ref field is an Int and so is t.People.
The SomeId value is the primary key of the related table. This issue is that there will not always be records in the Bookings table with a Ref value of Someid - so the query throws the following error.
I have seen others have got around this problem with catching the error, but from reading up on this and as per the error information it seems there should be a solution (in VB.NET) to cast the query or some of the fields in the query to nullable types?
Error is as follows:
The cast to value type 'Int32' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type.
When I declare two datatables and fill them both from a datatable returned by a function in class, that when i filter the one it seems to filter the other aswell?
For example:
I declare the datatable and initiate my class:
Dim DatatableOne As New Datatable
Dim DatatableTwo As New Datatable
Dim MyClass As New MyClass
I then call the function that returns a datatable and apply it to datatable1 and 2 Then fill two DataGrids with the table:
DatatableOne = MyClass.GetTable()
DatatableTwo = MyClass.GetTable()
DatatableOne.DefaultView.RowFilter = "Name = 'Tom'"
[CODE]...
For some reason i don't understand but both grids end up with the filtered data?
I'm trying to access the Count Property on the array of rows returned by the datatables select method, this is after converting the Web Project to 3.5
View 2 RepliesI am finding difficulties to convert a datatable to a new datatable using a reference datatable. My question is confusing and I am not good at explaining things so I drew a picture (see below).I have two datatables on memory and I need to create the third datatable using the second mapping table for reference. The column names are just for example and it can't be hardcoded.
View 2 RepliesI just upgraded a project from VB 2008 to VB 2010. Before, the project did not use LINQ. I have started implementing it. So, I have updated the target framework from 2.0 to 3.5, and added a reference to System.Core, and imported the namespace System.LINQ to the entire project and also imported System.Data.LINQ into the form I'm working with (because it was not available in the list for Imported Namespaces in the references tab).
It's not throwing any errors now, but my IntelliSense is not working for LINQ stuff.
For example... I write this:
[CODE]....................
Then, if I type S. on the next line, the IntelliSense doesn't grab what it should for S (Only get Equals, GetHashCode, GetType, ReferenceEquals, and ToString, instead of the options I should get like Count, First, FirstOrDefault, etc...). If I Type S.First. then its the same thing, no IntelliSense that lists the available fields for S, just the standard options (Equals, GetHashCode, GetType, ReferenceEquals, and ToString). I should be seeing my column names in my table when I type S.FirstOrDefault.
So any ideas what is going on? When I type the code, for example, MessageBox.Show(S.FirstOrDefault.FirstName), it works perfectly. But it doesn't change the casing of the text (so it would read s.firstordefault.firstname) and no intellisense while doing it. But no errors. BTW - Everything works perfectly when creating a NEW VS 2010 application, it's just my projects upgraded from Visual Basic 2008 that have this issue.
I have a DGV that has a datasource to load the rows I need for display.
Now, I need to save the selected rows to a DataTable.
binding the DGV. I created the DataTable in my DataSet dsProfiles1 and created a BindingSource - bsDataTableDGV
DataTable:
ClientID Int32 not null PK
ClientName String not null
ProgramNo Int32 Not Null
[Code].....
I have a form with a textbox and a add button. User can write a name down on the textbox and click add button. it will save in a datatable with auto ID. After that, the textbox is cleared and the user can write another name on the text box and click the button. This should add to the existing datatable on memory with existing ID + 1. Show on the gridview. (this is just for display purpose to confirm it works)
I have a datatable like this.
Button1.click() event
Dim name = txtname.Text
Dim dt As New DataTable
dt.Columns.Add("ID", GetType(Integer))
[Code] .....
At the moment I have sometime like the code above. in the real program, it is not just name and it is not just one datatable so i just mock up some code. And this code for aspx.
<asp:TextBox ID="txtname" runat="server">
</asp:TextBox><asp:Button ID="Button1" runat="server" Text="Button" />
<asp:GridView ID="GridView1" runat="server">
</asp:GridView>
I am creating an xml file with LINQ as follows...
Public Sub CreateXml()
Dim db As New MDataContext
Dim Customers = <gallery columns="3" rows="3">
[code]....
Could i mix local values with the ones returned from the LINQ query...Something like the following?
Public Sub CreateXml(ByVal **Col** As String, ByVal **Row** As String)
Dim db As New MDataContext
Dim Customers = <gallery columns="& **Col** &" rows="& **Row** &">
[code]...
I am trying to reference a DataTable and I do not know how to achieve this. I would like to assign dtTmp to dtTarget(i) through the reference dtCurr. Is it possible to achieve that in VB.NET?Private dtA, dtB As DataTable
Dim dtTarget() As DataTable = {Me.dtA, Me.dtB}
For i As Integer = 0 To dtTarget.Length - 1
dtTmp = New DataTable()
'Do something to dtTmp
assign the new table to the reference
dtTarget(i) = dtTmp