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• How is timezone handled in the lifecycle of an ADO.NET + SQL Server DateTime column?

  - by stimpy77

  Using SQL Server 2008. This is a really junior question and I could really use some elaborate information, but the information on Google seems to dance around the topic quite a bit and it would be nice if there was some detailed elaboration on how this works... Let's say I have a datetime column and in ADO.NET I set it to DateTime.UtcNow. 1) Does SQL Server store DateTime.UtcNow accordingly, or does it offset it again based on the timezone of where the server is installed, and then return it offset-reversed when queried? I think I know that the answer is "of course it stores it without offsetting it again" but want to be certain. So then I query for it and cast it from, say, an IDataReader column to a DateTime. As far as I know, System.DateTime has metadata that internally tracks whether it is a UTC DateTime or it is an offsetted DateTime, which may or may not cause .ToLocalTime() and .ToUniversalTime() to have different behavior depending on this state. So, 2) Does this casted System.DateTime object already know that it is a UTC DateTime instance, or does it assume that it has been offset? Now let's say I don't use UtcNow, I use DateTime.Now, when performing an ADO.NET INSERT or UPDATE. 3) Does ADO.NET pass the offset to SQL Server and does SQL Server store DateTime.Now with the offset metadata? So then I query for it and cast it from, say, an IDataReader column to a DateTime. 4) Does this casted System.DateTime object already know that it is an offset time, or does it assume that it is UTC?

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• In jQuery datepicker beforeShowDay if fails

  - by michalzuber

  HI. I'm having problem to highlight more days. Somehow the if statement in beforeShowDay isn't true when it should be :( dateString typeof is string and an example is available in the screenshot at http://mikaelz.host.sk/datepicker.png Pasted code: var dates = new Array(); function addDate(date) {if (jQuery.inArray(date, dates) < 0) dates.push(date);} function removeDate(index) {dates.splice(index, 1);} function addOrRemoveDate(date) { var index = jQuery.inArray(date, dates); if (index >= 0) removeDate(index); else addDate(date); } function padNumber(number) { var ret = new String(number); if (ret.length == 1) ret = "0" + ret; return ret; } jQuery(document).ready(function(){ jQuery("#pick-date").datepicker({ onSelect: function(dateText, inst) { addOrRemoveDate(dateText); }, beforeShowDay: function (date){ var year = date.getFullYear(); var month = padNumber(date.getMonth()); var day = padNumber(date.getDate()); var dateString = day + "." + month + "." + year; if (dates.indexOf(dateString) >= 0) { return [true,"ui-state-highlight"]; } return [true, ""]; } }); }); Big thanks for any good ideas what could be wrong.

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• Silverlight Timer problem

  - by jose

  Hello, I am developing a Silverlight application with custom animations. I want to update the variable animationCounter every 1 milissecond, so that in one second the value is 1000. I've tried DispatcherTimer and System.Threading.Timer. this way: DispatcherTimer timer = new DispatcherTimer(); (...) timer.Interval = new TimeSpan(0, 0, 0, 0, 1); timer.Tick += new EventHandler(timer_Tick); (...) (...) void timer_Tick(object sender, EventArgs e) { animationCounter++; Dispatcher.BeginInvoke(() => txtAnimationCounter.Text = animationCounter.ToString()); } with System.Threading.Timer System.Threading timer = null; timer = new System.Threading.Timer(UpdateAnimationCounter, 0, 1); void UpdateAnimationCounter(object state) { animationCounter++; Dispatcher.BeginInvoke(() => txtAnimationCounter.Text = animationCounter.ToString()); } Both of them are setting AnimationCounter around 100 in one second. Should be 1000. I don't know why. Is there anything I'm missing. Thanks

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• Is it possible to spoof or reuse VIEWSTATE or detect if it is protected from modification?

  - by Peter Jaric

  Question ASP and ASP.NET web applications use a value called VIEWSTATE in forms. From what I understand, this is used to persist some kind of state on the client between requests to the web server. I have never worked with ASP or ASP.NET and need some help with two questions (and some sub-questions): 1) Is it possible to programmatically spoof/construct a VIEWSTATE for a form? Clarification: can a program look at a form and from that construct the contents of the base64-encoded VIEWSTATE value? 1 a) Or can it always just be left out? 1 b) Can an old VIEWSTATE for a particular form be reused in a later invocation of the same form, or would it just be luck if that worked? 2) I gather from http://msdn.microsoft.com/en-us/library/ms972976.aspx#viewstate_topic12 that it is possible to turn on security so that the VIEWSTATE becomes secure from spoofing. Is it possible for a program to detect that a VIEWSTATE is safeguarded in such a way? 2 a) Is there a one-to-one mapping between the occurrence of EVENTVALIDATION values and secure VIEWSTATEs? Regarding 1) and 2), if yes, can I have a hint about how I would do that? For 2) I am thinking I could base64-decode the value and search for a string that always is found in unencrypted VIEWSTATEs. "First:"? Something else? Background I have made a small tool for detecting and exploiting so called CSRF vulnerabilities. I use it to quickly make proof of concepts of such vulnerabilities that I send to the affected site owners. Quite often I encounter these forms with a VIEWSTATE, and these I don't know if they are secure or not. Edit 1: Clarified question 1 somewhat. Edit 2: Added text in italics.

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• How not to lose binding source updates?

  - by Fyodor Soikin

  Suppose I have a modal dialog with a textbox and OK/Cancel buttons. And it is built on MVVM - i.e. it has a ViewModel object with a string property that the textbox is bound to. Say, I enter some text in the textbox and then grab my mouse and click "OK". Everything works fine: at the moment of click, the textbox loses focus, which causes the binding engine to update the ViewModel's property. I get my data, everybody's happy. Now suppose I don't use my mouse. Instead, I just hit Enter on the keyboard. This also causes the "OK" button to "click", since it is marked as IsDefault="True". But guess what? The textbox doesn not lose focus in this case, and therefore, the binding engine remains innocently ignorant, and I don't get my data. Dang! Another variation of the same scenario: suppose I have a data entry form right in the main window, enter some data into it, and then hit Ctrl+S for "Save". Guess what? My latest entry doesn't get saved! This may be somewhat remedied by using UpdateSourceTrigger=PropertyChanged, but that is not always possible. One obvious case would be the use of StringFormat with binding - the text keeps jumping back into "formatted" state as I'm trying to enter it. And another case, which I have encountered myself, is when I have some time-consuming processing in the viewmodel's property setter, and I only want to perform it when the user is "done" entering text. This seems like an eternal problem: I remember trying to solve it systematically from ages ago, ever since I've started working with interactive interfaces, but I've never quite succeeded. In the past, I always ended up using some sort of hacks - like, say, adding an "EnsureDataSaved" method to every "presenter" (as in "MVP") and calling it at "critical" points, or something like that... But with all the cool technologies, as well as empty hype, of WPF, I expected they'd come up with some good solution.

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• [VB.Net] TreeView update bug in the .net framework

  - by CFP

  Consider the following code: Dim Working As Boolean = False Private Sub TreeView1_AfterCheck(ByVal sender As Object, ByVal e As System.Windows.Forms.TreeViewEventArgs) Handles TreeView1.AfterCheck If Working Then Exit Sub Working = True e.Node.Checked = Not e.Node.Checked Working = False End Sub Private Sub TreeView1_MouseClick(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles TreeView1.MouseClick If e.Button = Windows.Forms.MouseButtons.Right Then MsgBox("Checked = " & TreeView1.SelectedNode.Checked) End Sub Where TreeView1 is a TreeView added to the form, with CheckBoxes set to true and one node added. The code basically cancel any node checking occuring on the form. Single-clicking the top node to check it works well : your click is immediately canceled. Yet if you double-click the checkbox, it will display a tick. But verifying the check state through a right click will yield a Checked = False dialog. How come? Is it a bug (I'm using the latest .Net Framework 4.0, and he same occurs in 2.0), or am I doing something wrong here? Is there a work around? Thanks! EDIT: Additionally, the MouseDoubleClick event is not raised before you click once again.

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• Bing Maps - Auto update location binding of pushpins

  - by abp

  Hi I'm using the Bing Maps control to display a series of custom pushpins, representing objects which are constantly moving around and changing state. Using databinding the various properties for the objects are being updated as they should, but for some reason this doesn't apply to their locations. I have the map bound to an ObservableCollection as such: <UserControl.Resources> <DataTemplate x:Key="PushpinTemplate"> <v:CustomPushpin /> </DataTemplate> </UserControl.Resources> ... <m:Map Name="map"> <m:MapItemsControl ItemTemplate="{StaticResource PushpinTemplate}" ItemsSource="{Binding Objects}" /> </m:Map> ...and in CustomPushpin: <UserControl ... m:MapLayer.Position="{Binding Location}" m:MapLayer.PositionOrigin="BottomCenter" mc:Ignorable="d" d:DesignHeight="126" d:DesignWidth="85"> Like all other properties, the Location of the individual objects are implemented using INotifyPropertyChanged. private Location _location; public Location Location { get { return _location; } set { _location = value; OnPropertyChanged("Location"); } } When the map is moving, either because of panning or zooming, the objects move, but othersize not. I can't quite figure if I'm doing something wrong here, or if it's a problem with the Bing Maps control. Any thought?

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• Loop to check all 14 days in the pay period

  - by Rachel Ann Arndt

  Name: Calc_Anniversary Input: Pay_Date, Hire_Date, Termination_Date Output: "Y" if is the anniversary of the employee's Hire_Date, "N" if it is not, and "T" if he has been terminated before his anniversary. Description: Create local variables to hold the month and day of the employee's Date_of_Hire, Termination_Date, and of the processing date using the TO_CHAR function. First check to see if he was terminated before his anniversary. The anniversary could be on any day during the pay period, so there will be a loop to check all 14 days in the pay period to see if one was his anniversary. CREATE OR replace FUNCTION Calc_anniversary( incoming_anniversary_date IN VARCHAR2) RETURN BOOLEAN IS hiredate VARCHAR2(20); terminationdate VARCHAR(20); employeeid VARCHAR2(38); paydate NUMBER := 0; BEGIN SELECT Count(arndt_raw_time_sheet_data.pay_date) INTO paydate FROM arndt_raw_time_sheet_data WHERE paydate = incoming_anniversary_date; WHILE paydate <= 14 LOOP SELECT To_char(employee_id, '999'), To_char(hire_date, 'DD-MON'), To_char(termination_date, 'DD-MON') INTO employeeid, hiredate, terminationdate FROM employees, time_sheet WHERE employees.employee_id = time_sheet.employee_id AND paydate = pay_date; IF terminationdate > hiredate THEN RETURN 'T'; ELSE IF To_char(SYSDATE, 'DD-MON') = To_char(hiredate, 'DD-MON')THEN RETURN 'Y'; ELSE RETURN 'N'; END IF; END IF; paydate := paydate + 1; END LOOP; END; Tables I am using CREATE TABLE Employees ( EMPLOYEE_ID INTEGER, FIRST_NAME VARCHAR2(15), LAST_NAME VARCHAR2(25), ADDRESS_LINE_ONE VARCHAR2(35), ADDRESS_LINE_TWO VARCHAR2(35), CITY VARCHAR2(28), STATE CHAR(2), ZIP_CODE CHAR(10), COUNTY VARCHAR2(10), EMAIL VARCHAR2(16), PHONE_NUMBER VARCHAR2(12), SOCIAL_SECURITY_NUMBER VARCHAR2(11), HIRE_DATE DATE, TERMINATION_DATE DATE, DATE_OF_BIRTH DATE, SPOUSE_ID INTEGER, MARITAL_STATUS CHAR(1), ALLOWANCES INTEGER, PERSONAL_TIME_OFF FLOAT, CONSTRAINT pk_employee_id PRIMARY KEY (EMPLOYEE_ID), CONSTRAINT fk_spouse_id FOREIGN KEY (SPOUSE_ID) REFERENCES EMPLOYEES (EMPLOYEE_ID)) / CREATE TABLE Arndt_Raw_Time_Sheet_data ( EMPLOYEE_ID INTEGER, PAY_DATE DATE, HOURS_WORKED FLOAT, SALES_AMOUNT FLOAT, CONSTRAINT pk_employee_id_pay_date_time PRIMARY KEY (EMPLOYEE_ID, PAY_DATE), CONSTRAINT fk_employee_id_time FOREIGN KEY (EMPLOYEE_ID) REFERENCES EMPLOYEES (EMployee_ID)); error FUNCTION Calc_Anniversary compiled Warning: execution completed with warning

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• How to get JTree expanded?

  - by Dzmitry Zhaleznichenka

  I have a wizard with several screens where user has to fill his/her details for further processing. At the second screen I have a radio group with three radio buttons that enable additional elements. To proceed, user has to choose one of them. When user selects third button, single-selection JTree filled in with data enables and user has to select an option from it. Then user has to press "Next" to get to next screen. The option he\she had selected is stored as a TreePath. So far so good. My problem is the following. If the user wants to come back from the following screen to the screen with a JTree, I want to provide him\her with the JTree expanded to the option that had been selected and to highlight the option. However, whatsoever I try to do for that (any combinations of expandPath, scrollPathToVisible, addSelectionPath, makeVisible) always provides me with a collapsed tree. I try to expand both leaves and nodes. My code looks like this: rbProcessJTree.setSelected(isProcessJTree()); if (null != getSelectedTablePath()){ trTables.addSelectionPath(getSelectedTablePath()); trTables.expandPath(getSelectedTablePath()); trTables.scrollPathToVisible(getSelectedTablePath()); } When setSelected() is called, state change listener is invoked that enables JTree. The model is loaded during the form initialization. Each time I switch between screens, I save the input data from previous screen and dispose it. Then, when I need to open previous screen back, I save data from the following screen, dispose it, load data to this screen and show it. So each time the screen is generating from scratch. Could you please explain, what sequence of operations has to be done to get JTree expanded in a newly created form,with data model loaded and selection path provided?

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• The correct usage of nested #pragma omp for directives

  - by GoldenLee

  The following code runs like a charm before OpenMP parallelization was applied. In fact, the following code was in a state of endless loop! I'm sure that's result from my incorrect use to the OpenMP directives. Would you please show me the correct way? Thank you very much. #pragma omp parallel for for (int nY = nYTop; nY <= nYBottom; nY++) { for (int nX = nXLeft; nX <= nXRight; nX++) { // Use look-up table for performance dLon = theApp.m_LonLatLUT.LonGrid()[nY][nX] + m_FavoriteSVISSRParams.m_dNadirLon; dLat = theApp.m_LonLatLUT.LatGrid()[nY][nX]; // If you don't want to use longitude/latitude look-up table, uncomment the following line //NOMGeoLocate.XYToGEO(dLon, dLat, nX, nY); if (dLon > 180 || dLat > 180) { continue; } if (Navigation.GeoToXY(dX, dY, dLon, dLat, 0) > 0) { continue; } // Skip void data scanline dY = dY - nScanlineOffset; // Compute coefficients as well as its four neighboring points' values nX1 = int(dX); nX2 = nX1 + 1; nY1 = int(dY); nY2 = nY1 + 1; dCx = dX - nX1; dCy = dY - nY1; dP1 = pIRChannelData->operator [](nY1)[nX1]; dP2 = pIRChannelData->operator [](nY1)[nX2]; dP3 = pIRChannelData->operator [](nY2)[nX1]; dP4 = pIRChannelData->operator [](nY2)[nX2]; // Bilinear interpolation usNomDataBlock[nY][nX] = (unsigned short)BilinearInterpolation(dCx, dCy, dP1, dP2, dP3, dP4); } }

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• How expensive is a context switch? Is it better to implement a manual task switch than to rely on OS

  - by Vilx-

  The title says it all. Imagine I have two (three, four, whatever) tasks that have to run in parallel. Now, the easy way to do this would be to create separate threads and forget about it. But on a plain old single-core CPU that would mean a lot of context switching - and we all know that context switching is big, bad, slow, and generally simply Evil. It should be avoided, right? On that note, if I'm writing the software from ground up anyway, I could go the extra mile and implement my own task-switching. Split each task in parts, save the state inbetween, and then switch among them within a single thread. Or, if I detect that there are multiple CPU cores, I could just give each task to a separate thread and all would be well. The second solution does have the advantage of adapting to the number of available CPU cores, but will the manual task-switch really be faster than the one in the OS core? Especially if I'm trying to make the whole thing generic with a TaskManager and an ITask, etc?

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• Segmentation fault on returning from main (very short and simple code, no arrays or pointers)

  - by Gábor Kovács

  I've been wondering why the following trivial code produces a segmentation fault when returning from main(): //Produces "Error while dumping state (probably corrupted stack); Segmentation fault" #include <iostream> #include <fstream> #include <vector> using namespace std; class Test { vector<int> numbers; }; int main() { Test a; ifstream infile; cout << "Last statement..." << endl; // this gets executed return 0; } Interestingly, 1) if only one of the two variables is declared, I don't get the error, 2) if I declare a vector variable instead of an object with a vector member, everything's fine, 3) if I declare an ofstream instead of an ifstream, again, everything works fine. Something appears to be wrong with this specific combination... Could this be a compiler bug? I use gcc version 3.4.4 with cygwin. Thanks for the tips in advance. Gábor

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• Is this feasbile with GIS?

  - by Gnu Engineer

  I'm just getting myself to familiarize with GIS but i like to know before hand if the following is feasible with current GIS apps/tools... I get the point for an address by geocoding. Easy part. Now if the point falls within a boundary (may be a city/county/state) then i need to get the data (any id/flag) associated with the boundary. Based on the id/flag i then apply some business logic. My question is... How do i define the boundary? What tools should i use for it? How can i store the boundary definition in database in order to check if the point falls within it? This has to be done in the back end and not in visual maps as we don't intend to show/use maps. How do i associate my custom data (id/flag) with the above boundary definition? Hope i'm having right assumption on capabilities of GIS. Most of examples what i see is around people trying to show maps with data which is exactly not what i'm looking for. Also please suggest me some tools/books on this.

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• Distinct or group by on some columns but not others

  - by Nazadus

  I have a view that I'm trying to filter with something similar to DISTINCT on some columns but not others. I have a view like this: Name LastName Zip Street1 HouseholdID (may not be unique because it may have multiple addresses -- think of it in the logical sense as grouping persons but not physical locations; If you lookup HouseholdID 4130, you may get two rows.. or more, because the person may have mutiple mailing locations) City State I need to pull all those columns but filter on LastName,Zip, and Street1. Here's the fun part: The filter is arbitrary -- meaning I don't care which one of the duplicates goes away. This is for a mail out type thing and the other information is not used for any other reason than than to look up a specific person if needed (I have no idea why). So.. given one of the records, you can easily figure out the removed ones. As it stands now, my Sql-Fu fails me and I'm filtering in C# which is incredibly slow and is pretty much a foreach that starts with an empty list and adds the row in if the combined last name, zip, and street aren't are not in the list. I feel like I'm missing a simple / basic part of SQL that I should be understanding.

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• CSV is actually .... Semicolon Separated Values ... (Excel export on AZERTY)

  - by Bugz R us

  I'm a bit confused here. When I use Excel 2003 to export a sheet to CSV, it actually uses semicolons ... Col1;Col2;Col3 shfdh;dfhdsfhd;fdhsdfh dgsgsd;hdfhd;hdsfhdfsh Now when I read the csv using Microsoft drivers, it expects comma's and sees the list as one big column ??? I suspect Excel is exporting with semicolons because I have a AZERTY keyboard. However, doesn't the CSV reader then also have to take in account the different delimiter ? How can I know the appropriate delimiter, and/or read the csv properly ?? public static DataSet ReadCsv(string fileName) { DataSet ds = new DataSet(); string pathName = System.IO.Path.GetDirectoryName(fileName); string file = System.IO.Path.GetFileName(fileName); OleDbConnection excelConnection = new OleDbConnection (@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + pathName + ";Extended Properties=Text;"); try { OleDbCommand excelCommand = new OleDbCommand(@"SELECT * FROM " + file, excelConnection); OleDbDataAdapter excelAdapter = new OleDbDataAdapter(excelCommand); excelConnection.Open(); excelAdapter.Fill(ds); } catch (Exception exc) { throw exc; } finally { if(excelConnection.State != ConnectionState.Closed ) excelConnection.Close(); } return ds; }

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• Recreating a workflow instance with the same instance id

  - by Miron Brezuleanu

  We have some objects that have an associated workflow instance. The objects are identified with a GUID, which is also the GUID of the workflow instance associated with the object. We need to restart (see NOTE 3 for the meaning of 'restart') the workflow instance if the workflow definition changed (there is no state in the workflow itself and it is written to support restarting in this manner). The restarting is performed by calling Terminate on the WorkflowInstance, then recreating the instance with the same GUID. The weird part is that this works every other attempt (odd attempts - the workflow is stopped, but for some reason doesn't restart, even attempt - the already terminated workflow is recreated and started successfully). While I admit that using 'second hand' GUIDs is a sign of extraordinary cheapness (and something we plan to change), I'm wondering why this isn't working. Any ideas? NOTES: The terminated workflow instance is passivated (waiting for a notification) at the time of the termination. The Terminate call successfully deletes the data persisted in the database for that instance. We're using 'restarting' with a meaning that's less common in the context of WF - not restarting a passivated instance, but force the workflow to start again from the beginning of its definition. Thanks!

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• Which OpenGL functions are not GPU-accelerated?

  - by Xavier Ho

  I was shocked when I read this (from the OpenGL wiki): glTranslate, glRotate, glScale Are these hardware accelerated? No, there are no known GPUs that execute this. The driver computes the matrix on the CPU and uploads it to the GPU. All the other matrix operations are done on the CPU as well : glPushMatrix, glPopMatrix, glLoadIdentity, glFrustum, glOrtho. This is the reason why these functions are considered deprecated in GL 3.0. You should have your own math library, build your own matrix, upload your matrix to the shader. For a very, very long time I thought most of the OpenGL functions use the GPU to do computation. I'm not sure if this is a common misconception, but after a while of thinking, this makes sense. Old OpenGL functions (2.x and older) are really not suitable for real-world applications, due to too many state switches. This makes me realise that, possibly, many OpenGL functions do not use the GPU at all. So, the question is: Which OpenGL function calls don't use the GPU? I believe knowing the answer to the above question would help me become a better programmer with OpenGL. Please do share some of your insights.

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• ExecuteNonQuery: Connection property has not been initialized

  - by 20151012

  I get an error in my code: The error point at dbcom.ExecuteNonQuery();. Code(connection) public admin_addemp() { InitializeComponent(); con = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\EMPS.accdb;Persist Security Info=True"); con.Open(); ds.Tables.Add(dt); ds.Tables.Add(dt2); } Code (Save button) private void save_btn_Click(object sender, EventArgs e) { OleDbCommand check = new OleDbCommand(); check.Connection = con; check.CommandText = "SELECT COUNT(*) FROM employeeDB WHERE ([EmployeeName]=?)"; check.Parameters.AddWithValue("@EmployeeName", tb_name.Text); if (Convert.ToInt32(check.ExecuteScalar()) == 0) { dbcom2 = new OleDbCommand("SELECT EmployeeID FROM employeeDB WHERE EmployeeID='" + tb_id.Text + "'", con); OleDbParameter param = new OleDbParameter(); param.ParameterName = tb_id.Text; dbcom.Parameters.Add(param); OleDbDataReader read = dbcom2.ExecuteReader(); if (read.HasRows) { MessageBox.Show("The Employee ID '" + tb_id.Text + "' already exist. Please choose another Employee ID."); read.Dispose(); read.Close(); } else { string q = "INSERT INTO employeeDB (EmployeeID, EmployeeName, IC, Address, State, " + " Postcode, DateHired, Phone, ManagerName) VALUES ('" + tb_id.Text + "', " + " '" + tb_name.Text + "', '" + tb_ic.Text + "', '" + tb_add1.Text + "', '" + cb_state.Text + "', " + " '" + tb_postcode.Text + "', '" + dateTimePicker1.Value + "', '" + tb_hp.Text + "', '" + cb_manager.Text + "')"; dbcom = new OleDbCommand(q, con); dbcom.ExecuteNonQuery(); MessageBox.Show("New Employee '" + tb_name.Text + "'- Successfuly Added."); } } else { MessageBox.Show("Employee name '" + tb_name.Text + "' already added into the database"); } ds.Dispose(); } I'm using Microsoft Access 2010 as my database and this is stand alone system. Please help me.

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• optimistic and pessimistic locks

  - by billmce

  Working on my first php/Codeigniter project and I’ve scoured the ‘net for information on locking access to editing data and haven’t found very much information. I expect it to be a fairly regular occurrence for 2 users to attempt to edit the same form simultaneously. My experience (in the stateful world of BBx, filePro, and other RAD apps) is that the data being edited is locked using a pessimistic lock—one user has access to the edit form at the time. The second user basically has to wait for the first to finish. I understand this can be done using Ajax sending XMLHttpRequests to maintain a ‘lock’ database. The php world, lacking state, seems to prefer optimistic locking. If I understand it correctly it works like this: both users get to access the data and they each record a ‘before changes’ version of the data. Before saving their changes, the data is once again retrieved and compared the ‘before changes’ version. If the two versions are identical then the users changes are written. If they are different; the user is shown what has changed since he/she started editing and some mechanism is added to resolve the differences—or the user is shown a ‘Sorry, try again’ message. I’m interested in any experience people here have had with implementing both pessimistic and optimistic locking. If there are any libraries, tools, or ‘how-to’s available I’m appreciate a link. Thanks

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• Is there a better way to throttle a high throughput job?

  - by ChaosPandion

  I created a simple class that shows what I am trying to do without any noise. Feel free to bash away at my code. That's why I posted it here. public class Throttled : IDisposable { private readonly Action work; private readonly Func<bool> stop; private readonly ManualResetEvent continueProcessing; private readonly Timer throttleTimer; private readonly int throttlePeriod; private readonly int throttleLimit; private int totalProcessed; public Throttled(Action work, Func<bool> stop, int throttlePeriod, int throttleLimit) { this.work = work; this.stop = stop; this.throttlePeriod = throttlePeriod; this.throttleLimit = throttleLimit; continueProcessing = new ManualResetEvent(true); throttleTimer = new Timer(ThrottleUpdate, null, throttlePeriod, throttlePeriod); } public void Dispose() { throttleTimer.Dispose(); ((IDisposable)continueProcessing).Dispose(); } public void Execute() { while (!stop()) { if (Interlocked.Increment(ref totalProcessed) > throttleLimit) { lock (continueProcessing) { continueProcessing.Reset(); } if (!continueProcessing.WaitOne(throttlePeriod)) { throw new TimeoutException(); } } work(); } } private void ThrottleUpdate(object state) { Interlocked.Exchange(ref totalProcessed, 0); lock (continueProcessing) { continueProcessing.Set(); } } }

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• How To perform a SQL Query to DataTable Operation That Can Be Cancelled

  - by David W

  I tried to make the title as specific as possible. Basically what I have running inside a backgroundworker thread now is some code that looks like: SqlConnection conn = new SqlConnection(connstring); SqlCommand cmd = new SqlCommand(query, conn); conn.Open(); SqlDataAdapter sda = new SqlDataAdapter(cmd); sda.Fill(Results); conn.Close(); sda.Dispose(); Where query is a string representing a large, time consuming query, and conn is the connection object. My problem now is I need a stop button. I've come to realize killing the backgroundworker would be worthless because I still want to keep what results are left over after the query is canceled. Plus it wouldn't be able to check the canceled state until after the query. What I've come up with so far: I've been trying to conceptualize how to handle this efficiently without taking too big of a performance hit. My idea was to use a SqlDataReader to read the data from the query piece at a time so that I had a "loop" to check a flag I could set from the GUI via a button. The problem is as far as I know I can't use the Load() method of a datatable and still be able to cancel the sqlcommand. If I'm wrong please let me know because that would make cancelling slightly easier. In light of what I discovered I came to the realization I may only be able to cancel the sqlcommand mid-query if I did something like the below (pseudo-code): while(reader.Read()) { //check flag status //if it is set to 'kill' fire off the kill thread //otherwise populate the datatable with what was read } However, it would seem to me this would be highly ineffective and possibly costly. Is this the only way to kill a sqlcommand in progress that absolutely needs to be in a datatable? Any help would be appreciated!

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• Could someone explain gtk2hs drag and drop to me, the listDND.hs demo just isn't doing it for me?

  - by Tom Carstens

  As the title says, I just don't get DND (or rather I understand the concept and I understand the order of callbacks, I just don't understand how to setup DND for actual usage.) I'd like to say that I've done DND stuff before in C, but considering I never really got that working... So I'm trying (and mostly succeeding, save DND) to write a text editor (using gtksourceview, because it has built in code highlighting.) Reasons are below if you want them. Anyways, there's not really a good DND demo or tutorial available for gtk2hs (listDND.hs just doesn't translate well in my head.) So what I'm asking is for code that demonstrates simple DND on a window widget (for example.) Ideally, it should accept drops from other windows (such as Thunar) and print out the information in string form. I think I can take it from there... Reasons: I'm running a fairly light weight setup, dwm and a few gtk+2 programs. I really don't want to have to pull in gtk+3 to get the current gedit from the repos (Arch Linux.) Currently, I'm using geany for all of my text editing needs, however, geany is a bit heavy for editing config files. Further, geany doesn't care for my terminal of choice (st;) so I don't even get the benefit of using it as an IDE. Meaning I'd like a lightweight text editor with syntax highlighting. I could configure emacs or vim or something, but that seems to me to be more of a hack then a proper solution. Thus my project was born. It's mostly working (aside from DND, all that's left is proper multi-tab support.) Admittedly, I could probably work this out if I wrote it in C, but there isn't that much state in a text editor so Haskell's been working fine with almost no need for mutable variables.

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• Cross-platform HTML application options

  - by Charles

  I'd like to develop a stand-alone desktop application targeting Windows (XP through 7) and Mac (Tiger through Snow Leopard), and if possible iPhone and Android. In order to make it all work with as much common code as possible (and because it's the only thing I'm good at), I'd like to handle the main logic with HTML and JS. Using Adobe AIR is a possibility. And I think I can do this with various application wrappers, using .NET for Windows XP, Objective C for iPhone, Java for Android and native "widget" platform support for Mac and Windows Vista & 7 (though I'd like to keep the widget in the foreground, so the Mac dashboard isn't ideal). Does anyone have any suggestions on where to start? The two sticking points are: I'll certainly need some form of persistent storage (cookies perhaps) to keep state between sessions I'll also probably need access to remote data files, so if I use AJAX and the hosting HTML file resides on the device, it will need to be able to do cross-domain requests. I've done this on the iPhone without any problems, but I'd be surprised if this were possible on other platforms. For me, Android and iPhone will be the easiest to handle, and it looks like I can use Adobe AIR to handle the rest. But I wanted to know if there are any other alternatives. Does anyone have any suggesions?

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• Domain validates but won't save

  - by marko

  I have the following setup. Class, say, Car that has a CarPart (belongsTo=[car:Car]). When I'm creating a Car I also want to create som default CarParts, so I do def car = new Car(bla bla bla) def part = new CarPart(car:car) Now, when I do car.validate() or part.validate() it seems fine. But when I do if(car.save && part.save() I get this exception: 2012-03-24 14:02:21,943 [http-8080-4] ERROR util.JDBCExceptionReporter - Batch entry 0 insert into car_part (version, car_id, id) values ('0', '297', '298') was aborted. Call getNextException to see the cause. 2012-03-24 14:02:21,943 [http-8080-4] ERROR util.JDBCExceptionReporter - ERROR: value too long for type character varying(6) 2012-03-24 14:02:21,943 [http-8080-4] ERROR events.PatchedDefaultFlushEventListener - Could not synchronize database state with session org.hibernate.exception.DataException: Could not execute JDBC batch update Stacktrace follows: java.sql.BatchUpdateException: Batch entry 0 insert into car_part (version, deal_id, id) values ('0', '297', '298') was aborted. Call getNextException to see the cause. at org.postgresql.jdbc2.AbstractJdbc2Statement$BatchResultHandler.handleError(AbstractJdbc2Statement.java:2621) at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1837) at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:407) at org.postgresql.jdbc2.AbstractJdbc2Statement.executeBatch(AbstractJdbc2Statement.java:2754) at $Proxy20.flush(Unknown Source) at ristretto.DealController$_closure5.doCall(DealController.groovy:109) at ristretto.DealController$_closure5.doCall(DealController.groovy) at java.lang.Thread.run(Thread.java:722) Any ideas?

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• iPhone OpenGLES: Textures are consuming too much memory and the program crashes with signal "0"

  - by CustomAppsMan

  I am not sure what the problem is. My app is running fine on the simulator but when I try to run it on the iPhone it crashes during debugging or without debugging with signal "0". I am using the Texture2D.m and OpenGLES2DView.m from the examples provided by Apple. I profiled the app on the iPhone with Instruments using the Memory tracer from the Library and when the app died the final memory consumed was about 60Mb real and 90+Mb virtual. Is there some other problem or is the iPhone just killing the application because it has consumed too much memory? If you need any information please state it and I will try to provide it. I am creating thousands of textures at load time which is why the memory consumption is so high. Really cant do anything about reducing the number of pics being loaded. I was running before on just UIImage but it was giving me really low frame rates. I read on this site that I should use OpenGLES for higher frame rates. Also sub question is there any way not to use UIImage to load the png file and then use the Texture class provided to create the texture for OpenGLES functions to use it for drawing? Is there some function in OpenGLES which will create a texture straight from a png file?

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