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  • Scheduling of jobs in the presence of constraints in Java

    - by Asgard
    I want to know how to implement a solution to this problem: A task is performed by running, by more people, some basic jobs with known duration in time units (days, months, etc..). The execution of the jobs could lead to the existence of time constraints: a job, for example, can not start if it is not over another (or others) and so on. I want to design and build an application to check the correctness of jobs activities and to propose a schedule of jobs, if any, which is respectful of the constraints. Input must provide the jobs and associated constraints. The expected output is the scheduling of jobs. The specification of an elementary job consists of the pair <jobs-id, duration> A constraint is expressed by means of a quintuple of the type <S/E, id-job1, B/A, S/E, id-job2> the beginning (S) or the end (E) of a jobs Id-job1, must take place before (B) / after (A) of the beginning (S) / end (E) of the Id-job2. If there are no dependencies between some jobs, then jobs can be done before, in parallel. As a simple example, consider the input: jobs jobs(0, 3) jobs(1, 4) jobs(2, 5) jobs(3, 3) jobs(4, 3) constraints constraints(S, 1, A, E, 0) constraints(S, 4, A, E, 2) Possible output: t 0 1 2 3 4 0 * - * * - 1 * - * * - 2 * - * * - 3 * - * * - 4 - * * - - 5 - * * - - 6 - * - - * 7 - * - - * 8 - * - - * 9 - - - - * How to code an efficient java scheduler(avoiding the intense backtracking if is possible) to manage the jobs with these constraints, as described??? I have seen a discussion on a thread in a forum where an user seems has solved the problem easily, but He haven't given enough details to the users to compile a working project(I'm noob), and I'm interested to know an effective implementation of the solution (without using external libraries). If someone help me, I'll give to him a very good feedback ;)

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  • Best way to enforce inter-table constraints inside database

    - by FerranB
    I looking for the best way to check for inter-table constraints an step forward of foreing keys. For instance, to check if a date child record value is between a range date on two parent rows columns. For instance: Parent table ID DATE_MIN DATE_MAX ----- ---------- ---------- 1 01/01/2009 01/03/2009 ... Child table PARENT_ID DATE ---------- ---------- 1 01/02/2009 1 01/12/2009 <--- HAVE TO FAIL! ... I see two approaches: Create materialized views on-commit as shown in this article (or other equivalent on other RDBMS). Use stored-procedures and triggers. Any other approach? Which is the best option? UPDATE: The motivation of this question is not about "putting the constraints on database or on application". I think this is a tired question and anyone does the way she loves. And, I'm sorry for detractors, I'm developing with constraints on database. From here, the question is "which is the best option to manage inter-table constraints on database?". I'm added "inside database" on the question title. UPDATE 2: Some one added the "oracle" tag. Of course materialized views are oracle-tools but I'm interested on any option regardless it's on oracle or others RDBMSs.

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  • How to program for constraints/rules

    - by Gaurav
    First the background, during interviews in the past, many times I have been asked to design some or other variation of card game as programming puzzle, and I have tried to design it in OO way, but I have never been satisfied with my solutions. However it was not until recently that I realized that I had been approaching the problem from the wrong direction. Specifically I was trying to solve the problem by modeling individual card as an object. Problem with this is individual cards don't have any non-trivial intrinsic behavior and therefore are not suitable (or primary) candidate as objects. What is interesting and important about cards are rules and constraints, such as there could be only four suits, or only thirteen cards in each suit. Of course, then there are any number of rules for games. So my questions are Are there any idioms/constructs/patterns to program for rules & constraints. How many in 1 can be applied in conjunction with OO paradigm.

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  • SQL Server Constraints Across Tables

    - by chama
    I have a SQL Server database with an Apartment table (which has columns FloorNum and BuildingID) and an ApartmentBuilding table (with column NumFloors). Is there any way to set up a constraint (using the SQL Server UI) to check that Apartment.FloorNum is greater than ApartmentBuilding.NumFloors? I tried this: FloorNum > ApartmentBuilding.NumFloors but now I realize that I somehow have to join the columns on the BuildingID, but I have no idea how to do that within a constraint. Thanks for your help!

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  • T-SQL foreign key check constraint

    - by PaN1C_Showt1Me
    When you create a foreign key constraint in a table and you create the script in MS SQL Management Studio, it looks like this. ALTER TABLE T1 WITH CHECK ADD CONSTRAINT FK_T1 FOREIGN KEY(project_id) REFERENCES T2 (project_id) GO ALTER TABLE T1 CHECK CONSTRAINT FK_T1 GO What I don't understand is what purpose has the second alter with check constraint. Isn't creating the FK constraint enough? Do you have to add the check constraint to assure reference integrity ? Another question: how would it look like then when you'd write it directly in the column definition? CREATE TABLE T1 ( my_column INT NOT NULL CONSTRAINT FK_T1 REFERENCES T2(my_column) ) Isn't this enough?

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  • One check constraint or multiple check constraints?

    - by RenderIn
    Any suggestions on whether fewer check constraints are better, or more? How should they be grouped if at all? Suppose I have 3 columns which are VARCHAR2(1 BYTE), each of which is a 'T'/'F' flag. I want to add a check constraint to each column specifying that only characters IN ('T', 'F') are allowed. Should I have 3 separate check constraints, one for each column: COL_1 IN ('T', 'F') COL_2 IN ('T', 'F') COL_3 IN ('T', 'F') Or a single check constraint: COL_1 IN ('T', 'F') AND COL_2 IN ('T', 'F') AND COL_3 IN ('T', 'F') My thoughts are it is best to keep these three separate, as the columns are logically unrelated to each other. The only case I would have a check constraint that examines more than one column is if there was some relationship between the value in one and the value in another, e.g.: (PARENT_CNT > 0 AND PRIMARY_PARENT IS NOT NULL) OR (PARENT_CNT = 0 AND PRIMARY_PARENT IS NULL)

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  • SQL CHECK constraint issues

    - by blahblah
    I'm using SQL Server 2008 and I have a table with three columns: Length, StartTime and EndTime. I want to make a CHECK constraint on this table which says that: if Length == NULL then StartTime <> NULL and EndTime <> NULL else StartTime == NULL and EndTime == NULL I've begun to try things like this: Length == NULL AND StartTime <> NULL AND EndTime <> NULL Obviously this is not enough, but even this simple expression will not validate. I get the error: "Error validating 'CK_Test_Length_Or_Time'. Do you want to edit the constraint?" Any ideas on how to go about doing this?

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  • Java JTextPane JScrollPane Display Issue

    - by ikurtz
    The following class implements a chatGUI. When it runs okay the screen looks like this: Fine ChatGUI The problem is very often when i enter text of large length ie. 50 - 100 chars the gui goes crazy. the chat history box shrinks as shown in this image. Any ideas regarding what is causing this? Thank you. package Sartre.Connect4; import javax.swing.*; import java.net.*; import java.awt.*; import java.awt.event.*; import javax.swing.text.StyledDocument; import javax.swing.text.Style; import javax.swing.text.StyleConstants; import javax.swing.text.BadLocationException; import java.io.BufferedOutputStream; import javax.swing.text.html.HTMLEditorKit; import java.io.FileOutputStream; import java.io.IOException; import java.io.FileNotFoundException; import javax.swing.filechooser.FileNameExtensionFilter; import javax.swing.JFileChooser; /** * Chat form class * @author iAmjad */ public class ChatGUI extends JDialog implements ActionListener { /** * Used to hold chat history data */ private JTextPane textPaneHistory = new JTextPane(); /** * provides scrolling to chat history pane */ private JScrollPane scrollPaneHistory = new JScrollPane(textPaneHistory); /** * used to input local message to chat history */ private JTextPane textPaneHome = new JTextPane(); /** * Provides scrolling to local chat pane */ private JScrollPane scrollPaneHomeText = new JScrollPane(textPaneHome); /** * JLabel acting as a statusbar */ private JLabel statusBar = new JLabel("Ready"); /** * Button to clear chat history pane */ private JButton JBClear = new JButton("Clear"); /** * Button to save chat history pane */ private JButton JBSave = new JButton("Save"); /** * Holds contentPane */ private Container containerPane; /** * Layout GridBagLayout manager */ private GridBagLayout gridBagLayout = new GridBagLayout(); /** * GridBagConstraints */ private GridBagConstraints constraints = new GridBagConstraints(); /** * Constructor for ChatGUI */ public ChatGUI(){ setTitle("Chat"); // set up dialog icon URL url = getClass().getResource("Resources/SartreIcon.jpg"); ImageIcon imageIcon = new ImageIcon(url); Image image = imageIcon.getImage(); this.setIconImage(image); this.setAlwaysOnTop(true); setLocationRelativeTo(this.getParent()); //////////////// End icon and placement ///////////////////////// // Get pane and set layout manager containerPane = getContentPane(); containerPane.setLayout(gridBagLayout); ///////////////////////////////////////////////////////////// //////////////// Begin Chat History ////////////////////////////// textPaneHistory.setToolTipText("Chat History Window"); textPaneHistory.setEditable(false); textPaneHistory.setPreferredSize(new Dimension(350,250)); scrollPaneHistory.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS); scrollPaneHistory.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER); // fill Chat History GridBagConstraints constraints.gridx = 0; constraints.gridy = 0; constraints.gridwidth = 10; constraints.gridheight = 10; constraints.weightx = 100; constraints.weighty = 100; constraints.fill = GridBagConstraints.BOTH; constraints.anchor = GridBagConstraints.CENTER; constraints.insets = new Insets(10,10,10,10); constraints.ipadx = 0; constraints.ipady = 0; gridBagLayout.setConstraints(scrollPaneHistory, constraints); // add to the pane containerPane.add(scrollPaneHistory); /////////////////////////////// End Chat History /////////////////////// ///////////////////////// Begin Home Chat ////////////////////////////// textPaneHome.setToolTipText("Home Chat Message Window"); textPaneHome.setPreferredSize(new Dimension(200,50)); textPaneHome.addKeyListener(new MyKeyAdapter()); scrollPaneHomeText.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS); scrollPaneHomeText.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER); // fill Chat History GridBagConstraints constraints.gridx = 0; constraints.gridy = 10; constraints.gridwidth = 6; constraints.gridheight = 1; constraints.weightx = 100; constraints.weighty = 100; constraints.fill = GridBagConstraints.BOTH; constraints.anchor = GridBagConstraints.CENTER; constraints.insets = new Insets(10,10,10,10); constraints.ipadx = 0; constraints.ipady = 0; gridBagLayout.setConstraints(scrollPaneHomeText, constraints); // add to the pane containerPane.add(scrollPaneHomeText); ////////////////////////// End Home Chat ///////////////////////// ///////////////////////Begin Clear Chat History //////////////////////// JBClear.setToolTipText("Clear Chat History"); // fill Chat History GridBagConstraints constraints.gridx = 6; constraints.gridy = 10; constraints.gridwidth = 2; constraints.gridheight = 1; constraints.weightx = 100; constraints.weighty = 100; constraints.fill = GridBagConstraints.BOTH; constraints.anchor = GridBagConstraints.CENTER; constraints.insets = new Insets(10,10,10,10); constraints.ipadx = 0; constraints.ipady = 0; gridBagLayout.setConstraints(JBClear, constraints); JBClear.addActionListener(this); // add to the pane containerPane.add(JBClear); ///////////////// End Clear Chat History //////////////////////// /////////////// Begin Save Chat History ////////////////////////// JBSave.setToolTipText("Save Chat History"); constraints.gridx = 8; constraints.gridy = 10; constraints.gridwidth = 2; constraints.gridheight = 1; constraints.weightx = 100; constraints.weighty = 100; constraints.fill = GridBagConstraints.BOTH; constraints.anchor = GridBagConstraints.CENTER; constraints.insets = new Insets(10,10,10,10); constraints.ipadx = 0; constraints.ipady = 0; gridBagLayout.setConstraints(JBSave, constraints); JBSave.addActionListener(this); // add to the pane containerPane.add(JBSave); ///////////////////// End Save Chat History ///////////////////// /////////////////// Begin Status Bar ///////////////////////////// constraints.gridx = 0; constraints.gridy = 11; constraints.gridwidth = 10; constraints.gridheight = 1; constraints.weightx = 100; constraints.weighty = 50; constraints.fill = GridBagConstraints.BOTH; constraints.anchor = GridBagConstraints.CENTER; constraints.insets = new Insets(0,10,5,0); constraints.ipadx = 0; constraints.ipady = 0; gridBagLayout.setConstraints(statusBar, constraints); // add to the pane containerPane.add(statusBar); ////////////// End Status Bar //////////////////////////// // set resizable to false this.setResizable(false); // pack the GUI pack(); } /** * Deals with necessary menu click events * @param event */ public void actionPerformed(ActionEvent event) { Object source = event.getSource(); // Process Clear button event if (source == JBClear){ textPaneHistory.setText(null); statusBar.setText("Chat History Cleared"); } // Process Save button event if (source == JBSave){ // process only if there is data in history pane if (textPaneHistory.getText().length() > 0){ // process location where to save the chat history file JFileChooser chooser = new JFileChooser(); chooser.setMultiSelectionEnabled(false); chooser.setAcceptAllFileFilterUsed(false); FileNameExtensionFilter filter = new FileNameExtensionFilter("HTML Documents", "htm", "html"); chooser.setFileFilter(filter); int option = chooser.showSaveDialog(ChatGUI.this); if (option == JFileChooser.APPROVE_OPTION) { // Set up document to be parsed as HTML StyledDocument doc = (StyledDocument)textPaneHistory.getDocument(); HTMLEditorKit kit = new HTMLEditorKit(); BufferedOutputStream out; try { // add final file name and extension String filePath = chooser.getSelectedFile().getAbsoluteFile() + ".html"; out = new BufferedOutputStream(new FileOutputStream(filePath)); // write out the HTML document kit.write(out, doc, doc.getStartPosition().getOffset(), doc.getLength()); } catch (FileNotFoundException e) { JOptionPane.showMessageDialog(ChatGUI.this, "Application will now close. \n A restart may cure the error!\n\n" + e.getMessage(), "Fatal Error", JOptionPane.WARNING_MESSAGE, null); System.exit(2); } catch (IOException e){ JOptionPane.showMessageDialog(ChatGUI.this, "Application will now close. \n A restart may cure the error!\n\n" + e.getMessage(), "Fatal Error", JOptionPane.WARNING_MESSAGE, null); System.exit(3); } catch (BadLocationException e){ JOptionPane.showMessageDialog(ChatGUI.this, "Application will now close. \n A restart may cure the error!\n\n" + e.getMessage(), "Fatal Error", JOptionPane.WARNING_MESSAGE, null); System.exit(4); } statusBar.setText("Chat History Saved"); } } } } /** * Process return key for sending the message */ private class MyKeyAdapter extends KeyAdapter { @Override @SuppressWarnings("static-access") public void keyPressed(KeyEvent ke) { DateTime dateTime = new DateTime(); String nowdateTime = dateTime.getDateTime(); int kc = ke.getKeyCode(); if (kc == ke.VK_ENTER) { try { // Process only if there is data if (textPaneHome.getText().length() > 0){ // Add message origin formatting StyledDocument doc = (StyledDocument)textPaneHistory.getDocument(); Style style = doc.addStyle("HomeStyle", null); StyleConstants.setBold(style, true); String home = "Home [" + nowdateTime + "]: "; doc.insertString(doc.getLength(), home, style); StyleConstants.setBold(style, false); doc.insertString(doc.getLength(), textPaneHome.getText() + "\n", style); // update caret location textPaneHistory.setCaretPosition(doc.getLength()); textPaneHome.setText(null); statusBar.setText("Message Sent"); } } catch (BadLocationException e) { JOptionPane.showMessageDialog(ChatGUI.this, "Application will now close. \n A restart may cure the error!\n\n" + e.getMessage(), "Fatal Error", JOptionPane.WARNING_MESSAGE, null); System.exit(1); } ke.consume(); } } } }

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  • Poll Results: Foreign Key Constraints

    - by Darren Gosbell
    A few weeks ago I did the following post asking people – if they used foreign key constraints in their star schemas. The poll is still open if you are interested in adding to it, but here is what the chart looks like as of today. (at the bottom of the poll itself there is a link to the live results, unfortunately I cannot link the live results in here as the blogging platform blocks the required javascript)   Interestingly the results are fairly even. Of the 78 respondents, fractionally over half at least aim to start with referential integrity in their star schemas. I did not want to influence the results by sharing my opinion, but my personal preference is to always aim to have foreign key constraints. But at the same time, I am pragmatic about it, I do have projects where for various reasons some constraints are not defined. And I also have other designs that I have inherited, where it would just be too much work to go back and add foreign key constraints. If you are going to implement foreign keys in your star schema, they really need to be there at the start. In fact this poll was was the result of a feature request for BIDSHelper asking for a feature to check for null/missing foreign keys and I am entirely convinced that BIDS is the wrong place for this sort of functionality. BIDS is a design tool, your data needs to be constantly checked for consistency. It's not that I think that it's impossible to get a design working without foreign key constraints, but I like the idea of failing as soon as possible if there is an error and enforcing foreign key constraints lets me "fail early" if there are constancy issues with my data. By far the biggest concern with foreign keys is performance and I suppose I'm curious as to how often people actually measure and quantify this. I worked on a project a number of years ago that had very large data volumes and we did find that foreign key constraints did have a measurable impact, but what we did was to disable the constraints before loading the data, then enabled and checked them afterwards. This saved as time (although not as much as not having constraints at all), but still let us know early in the process if there were any consistency issues. For the people that do not have consistent data, if you have ETL processes that you control that are building your star schema which you also control, then to be blunt you only have yourself to blame. It is the job of the ETL process to make the data consistent. There are techniques for handling situations like missing data as well as  early and late arriving data. Ralph Kimball's book – The Data Warehouse Toolkit goes through some design patterns for handling data consistency. Having foreign key relationships can also help the relational engine to optimize queries as noted in this recent blog post by Boyan Penev

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  • AWT Textfield behaves weird with MicroSoft JVM

    - by AKh
    Hi, I am facing a weird problem when using MicroSoft JVM to run my Applet. I have an AWT panel with 4 textfields which is added to a dialog box. Everything goes fine until I enter a decimal value into the textfield and close the dialog box. When i reopen the dialog box the textfield inside the panel with all the decimal digits (entered in the previous step) behaves weird. The decimal values along with the WHITE area inside the textfield moves to the left and hides the digits. When I click inside the textfield it becomes normal. The Panel earlier had gridlayout and I even tried changing it to gridbaylayout and still the problem persist. NOTE: All Development are pertained to JRE1.1 to compatibility with MS JVM If any can help me with this it would be a great help. Thanks in advance. . . . . public MyPanel(Dialog myDialog) { Panel panel = new Panel(); this.dialog = myDialog; //Previous code with grid layout /* panel.setLayout(new GridLayout2(4,2,2,2)); panel.add(new Label("Symbol:")); panel.add(symbolField = new TextField("",20)); panel.add(new Label("Quantity:")); panel.add( qtyField = new TextField()); panel.add(new Label("Price per Share:")); panel.add( costField = new TextField()); panel.add(new Label("Date Acquired:")); panel.add( purchaseDate = new TextField() );*/ GridBagLayout gridbag = new GridBagLayout(); System.out.println("######## Created New GridBagLayout"); GridBagConstraints constraints = new GridBagConstraints(); panel.setLayout( gridbag ); constraints = buildConstraints( constraints, 0, 0, 1, 1, 1.5, 1 ); constraints.anchor = GridBagConstraints.WEST; constraints.fill = GridBagConstraints.HORIZONTAL; panel.add( new Label("Symbol:"), constraints); constraints = buildConstraints( constraints, 1, 0, 1, 1, 1.5, 1 ); constraints.anchor = GridBagConstraints.WEST; constraints.fill = GridBagConstraints.HORIZONTAL; panel.add( symbolField = new TextField("",20), constraints); constraints = buildConstraints( constraints, 0, 1, 1, 1, 1.5, 1 ); constraints.anchor = GridBagConstraints.WEST; constraints.fill = GridBagConstraints.HORIZONTAL; panel.add( new Label("Quantity:"), constraints); constraints = buildConstraints( constraints, 1, 1, 1, 1, 1.5, 1 ); constraints.anchor = GridBagConstraints.WEST; constraints.fill = GridBagConstraints.HORIZONTAL; panel.add( qtyField = new TextField(), constraints); constraints = buildConstraints( constraints, 0, 2, 1, 1, 1.5, 1 ); constraints.anchor = GridBagConstraints.WEST; constraints.fill = GridBagConstraints.HORIZONTAL; panel.add( new Label("Price per Share:"), constraints); constraints = buildConstraints( constraints, 1, 2, 1, 1, 1.5, 1 ); constraints.anchor = GridBagConstraints.WEST; constraints.fill = GridBagConstraints.HORIZONTAL; panel.add( costField = new TextField(), constraints); constraints = buildConstraints( constraints, 0, 3, 1, 1, 1.5, 1 ); constraints.anchor = GridBagConstraints.WEST; constraints.fill = GridBagConstraints.HORIZONTAL; panel.add( new Label("Date Acquired:"), constraints); constraints = buildConstraints( constraints, 1, 3, 1, 1, 1.5, 1 ); constraints.anchor = GridBagConstraints.WEST; constraints.fill = GridBagConstraints.HORIZONTAL; panel.add( purchaseDate = new TextField(), constraints); .............. ......... }

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  • Model login constraints based on time

    - by DaDaDom
    Good morning, for an existing web application I need to implement "time based login constraints". It means that for each user, later maybe each group, I can define timeslots when they are (not) allowed to log in into the system. As all data for the application is stored in database tables, I need to somehow create a way to model this idea in that way. My first approach, I will try to explain it here: Create a tree of login constraints (called "timeslots") with the main "categories", like "workday", "weekend", "public holiday", etc. on the top level, which are in a "sorted" order (meaning "public holiday" has a higher priority than "weekday") for each top level node create subnodes, which have a finer timespan, like "monday", "tuesday", ... below that, create an "hour" level: 0, 1, 2, ..., 23. No further details are necessary. set every member to "allowed" by default For every member of the system create a 1:n relationship member:timeslots which defines constraints, e.g. a member A may have A:monday-forbidden and A:tuesday-forbidden Do a depth-first search at every login and check if the member has a constraint. Why a depth first search? Well, I thought that it may be that a member has the rules: A:monday->forbidden, A:monday-10->allowed, A:mondey-11->allowed So a login on monday at 12:30 would fail, but one at 10:30 succeed. For performance reasons I could break the relational database paradigm and set a flag for every entry in the member-to-timeslots-table which is set to true if the member has information set for "finer" timeslots, but that's a second step. Is this model in principle a good idea? Are there existing models? Thanks.

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  • Login - check database if user exists... (c#)

    - by SAMIR BHOGAYTA
    I have managed to do the following... string connectionString = "datasource=localhost;username=xxx;password=xxx;database=xxx"; MySqlConnection mySqlConnection = new MySqlConnection(connectionString); string selectString = "SELECT username, password " + "FROM forum_members " + "WHERE username = '" + frmUsername.Text + "' AND password = '" + frmPassword.Text + "'"; MySqlCommand mySqlCommand = new MySqlCommand(selectString, mySqlConnection); mySqlConnection.Open(); String strResult = String.Empty; strResult = (String)mySqlCommand.ExecuteScalar(); mySqlConnection.Close(); if (strResult.Length == 0) { Label1.Text = "INCORRECT USER/PASS!" //could redirect to register page } else { Label1.Text = "YOU ARE LOGGED IN!"; //set loggin in sessions variables }

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  • MVC ActionLink generating NON-Restul URL AFTER adding constraints

    - by brianstewey
    Hello I have a custom route that without constraints generates a Restful URL with an ActionLink. Route - routes.MapRoute( "Blog", // Route name "Blog/{d}/{m}/{y}", // URL with parameters, new { controller = "Blog", action = "Retrieve" } Generates - http://localhost:2875/Blog/12/1/2010 From - <%=Html.ActionLink("Blog Entry - 12/01/2010", "Retrieve", "Blog", new { d = 12, m = 01, y = 2010 }, null)%> If I add constraints like so. routes.MapRoute( "Blog", // Route name "Blog/{d}/{m}/{y}", // URL with parameters, new { controller = "Blog", action = "Retrieve" }, new { d = @"\d{2}", m = @"\d{2}", y = @"\d{4}" } It generates - http://localhost:2875/Blog/Retrieve?d=12&m=1&y=2010 Extra information: it is added before the custom route. Any ideas? Cheers

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  • Mysterious constraints problem with SQL Server 2000

    - by Ramon
    Hi all I'm getting the following error from a VB NET web application written in VS 2003, on framework 1.1. The web app is running on Windows Server 2000, IIS 5, and is reading from a SQL server 2000 database running on the same machine. System.Data.ConstraintException: Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints. at System.Data.DataSet.FailedEnableConstraints() at System.Data.DataSet.EnableConstraints() at System.Data.DataSet.set_EnforceConstraints(Boolean value) at System.Data.DataTable.EndLoadData() at System.Data.Common.DbDataAdapter.FillFromReader(Object data, String srcTable, IDataReader dataReader, Int32 startRecord, Int32 maxRecords, DataColumn parentChapterColumn, Object parentChapterValue) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, String srcTable, IDataReader dataReader, Int32 startRecord, Int32 maxRecords) at System.Data.Common.DbDataAdapter.FillFromCommand(Object data, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet) The problem appears when the web app is under a high load. The system runs fine when volume is low, but when the number of requests becomes high, the system starts rejecting incoming requests with the above exception message. Once the problem appears, very few requests actually make it through and get processed normally, about 2 in every 30. The vast majority of requests fail, until a SQL Server restart or IIS reset is performed. The system then start processing requests normally, and after some time it starts throwing the same error. The error occurs when a data adapter runs the Fill() method against a SELECT statement, to populate a strongly-typed dataset. It appears that the dataset does not like the data it is given and throws this exception. This error occurs on various SELECT statements, acting on different tables. I have regenerated the dataset and checked the relevant constraints, as well as the table from which the data is read. Both the dataset definition and the data in the table are fine. Admittedly, the hardware running both the web app and SQL Server 2000 is seriously outdated, considering the numbers of incoming requests it currently receives. The amount of RAM consumed by SQL Server is dynamically allocated, and at peak times SQL Server can consume up to 2.8 GB out of a total of 3.5 GB on the server. At first I suspected some sort of index or database corruption, but after running DBCC CHECKDB, no errors were found in the database. So now I'm wondering whether this error is a result of the hardware limitations of the system. Is it possible for SQL Server to somehow mess up the data it's supposed to pass to the dataset, resulting in constraint violation due to, say, data type/length mismatch? I tried accessing the RowError messages of the data rows in the retrieved dataset tables but I kept getting empty strings. I know that HasErrors = true for the datatables in question. I have not set the EnableConstraints = false, and I don't want to do that. Thanks in advance. Ray

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  • MS SQL Bridge Table Constraints

    - by greg
    Greetings - I have a table of Articles and a table of Categories. An Article can be used in many Categories, so I have created a table of ArticleCategories like this: BridgeID int (PK) ArticleID int CategoryID int Now, I want to create constraints/relationships such that the ArticleID-CategoryID combinations are unique AND that the IDs must exist in the respective primary key tables (Articles and Categories). I have tried using both VS2008 Server Explorer and Enterprise Manager (SQL-2005) to create the FK relationships, but the results always prevent Duplicate ArticleIDs in the bridge table, even though the CategoryID is different. I am pretty sure I am doing something obviously wrong, but I appear to have a mental block at this point. Can anyone tell me please how should this be done? Greaty appreciated!

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  • ASP.NET JavaScript Routing for ASP.NET MVC–Constraints

    - by zowens
    If you haven’t had a look at my previous post about ASP.NET routing, go ahead and check it out before you read this post: http://weblogs.asp.net/zowens/archive/2010/12/20/asp-net-mvc-javascript-routing.aspx And the code is here: https://github.com/zowens/ASP.NET-MVC-JavaScript-Routing   Anyways, this post is about routing constraints. A routing constraint is essentially a way for the routing engine to filter out route patterns based on the day from the URL. For example, if I have a route where all the parameters are required, I could use a constraint on the required parameters to say that the parameter is non-empty. Here’s what the constraint would look like: Notice that this is a class that inherits from IRouteConstraint, which is an interface provided by System.Web.Routing. The match method returns true if the value is a match (and can be further processed by the routing rules) or false if it does not match (and the route will be matched further along the route collection). Because routing constraints are so essential to the route matching process, it was important that they be part of my JavaScript routing engine. But the problem is that we need to somehow represent the constraint in JavaScript. I made a design decision early on that you MUST put this constraint into JavaScript to match a route. I didn’t want to have server interaction for the URL generation, like I’ve seen in so many applications. While this is easy to maintain, it causes maintenance issues in my opinion. So the way constraints work in JavaScript is that the constraint as an object type definition is set on the route manager. When a route is created, a new instance of the constraint is created with the specific parameter. In its current form the constraint function MUST return a function that takes the route data and will return true or false. You will see the NotEmpty constraint in a bit. Another piece to the puzzle is that you can have the JavaScript exist as a string in your application that is pulled in when the routing JavaScript code is generated. There is a simple interface, IJavaScriptAddition, that I have added that will be used to output custom JavaScript. Let’s put it all together. Here is the NotEmpty constraint. There’s a few things at work here. The constraint is called “notEmpty” in JavaScript. When you add the constraint to a parameter in your C# code, the route manager generator will look for the JsConstraint attribute to look for the name of the constraint type name and fallback to the class name. For example, if I didn’t apply the “JsConstraint” attribute, the constraint would be called “NotEmpty”. The JavaScript code essentially adds a function to the “constraintTypeDefs” object on the “notEmpty” property (this is how constraints are added to routes). The function returns another function that will be invoked with routing data. Here’s how you would use the NotEmpty constraint in C# and it will work with the JavaScript routing generator. The only catch to using route constraints currently is that the following is not supported: The constraint will work in C# but is not supported by my JavaScript routing engine. (I take pull requests so if you’d like this… go ahead and implement it).   I just wanted to take this post to explain a little bit about the background on constraints. I am looking at expanding the current functionality, but for now this is a good start. Thanks for all the support with the JavaScript router. Keep the feedback coming!

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  • SQL Constraints &ndash; CHECK and NOCHECK

    - by David Turner
    One performance issue i faced at a recent project was with the way that our constraints were being managed, we were using Subsonic as our ORM, and it has a useful tool for generating your ORM code called SubStage – once configured, you can regenerate your DAL code easily based on your database schema, and it can even be integrated into your build as a pre-build event if you want to do this.  SubStage also offers the useful feature of being able to generate DDL scripts for your entire database, and can script your data for you too. The problem came when we decided to use the generate scripts feature to migrate the database onto a test database instance – it turns out that the DDL scripts that it generates include the WITH NOCHECK option, so when we executed them on the test instance, and performed some testing, we found that performance wasn’t as expected. A constraint can be disabled, enabled but not trusted, or enabled and trusted.  When it is disabled, data can be inserted that violates the constraint because it is not being enforced, this is useful for bulk load scenarios where performance is important.  So what does it mean to say that a constraint is trusted or not trusted?  Well this refers to the SQL Server Query Optimizer, and whether it trusts that the constraint is valid.  If it trusts the constraint then it doesn’t check it is valid when executing a query, so the query can be executed much faster. Here is an example base in this article on TechNet, here we create two tables with a Foreign Key constraint between them, and add a single row to each.  We then query the tables: 1 DROP TABLE t2 2 DROP TABLE t1 3 GO 4 5 CREATE TABLE t1(col1 int NOT NULL PRIMARY KEY) 6 CREATE TABLE t2(col1 int NOT NULL) 7 8 ALTER TABLE t2 WITH CHECK ADD CONSTRAINT fk_t2_t1 FOREIGN KEY(col1) 9 REFERENCES t1(col1) 10 11 INSERT INTO t1 VALUES(1) 12 INSERT INTO t2 VALUES(1) 13 GO14 15 SELECT COUNT(*) FROM t2 16 WHERE EXISTS17 (SELECT *18 FROM t1 19 WHERE t1.col1 = t2.col1) This all works fine, and in this scenario the constraint is enabled and trusted.  We can verify this by executing the following SQL to query the ‘is_disabled’ and ‘is_not_trusted’ properties: 1 select name, is_disabled, is_not_trusted from sys.foreign_keys This gives the following result: We can disable the constraint using this SQL: 1 alter table t2 NOCHECK CONSTRAINT fk_t2_t1 And when we query the constraints again, we see that the constraint is disabled and not trusted: So the constraint won’t be enforced and we can insert data into the table t2 that doesn’t match the data in t1, but we don’t want to do this, so we can enable the constraint again using this SQL: 1 alter table t2 CHECK CONSTRAINT fk_t2_t1 But when we query the constraints again, we see that the constraint is enabled, but it is still not trusted: This means that the optimizer will check the constraint each time a query is executed over it, which will impact the performance of the query, and this is definitely not what we want, so we need to make the constraint trusted by the optimizer again.  First we should check that our constraints haven’t been violated, which we can do by running DBCC: 1 DBCC CHECKCONSTRAINTS (t2) Hopefully you see the following message indicating that DBCC completed without finding any violations of your constraint: Having verified that the constraint was not violated while it was disabled, we can simply execute the following SQL:   1 alter table t2 WITH CHECK CHECK CONSTRAINT fk_t2_t1 At first glance this looks like it must be a typo to have the keyword CHECK repeated twice in succession, but it is the correct syntax and when we query the constraints properties, we find that it is now trusted again: To fix our specific problem, we created a script that checked all constraints on our tables, using the following syntax: 1 ALTER TABLE t2 WITH CHECK CHECK CONSTRAINT ALL

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  • Using Constraints on Hierarchical Data in a Self-Referential Table

    - by pbarney
    Suppose you have the following table, intended to represent hierarchical data: +--------+-------------+ | Field | Type | +--------+-------------+ | id | int(10) | | parent | int(10) | | name | varchar(45) | +--------+-------------+ The table is self-referential in that the parent_id refers to id. So you might have the following data: +----+--------+---------------+ | id | parent | name | +----+--------+---------------+ | 1 | 0 | fruit | | 2 | 0 | vegetable | | 3 | 1 | apple | | 4 | 1 | orange | | 5 | 3 | red delicious | | 6 | 3 | granny smith | | 7 | 3 | gala | +----+--------+---------------+ Using MySQL, I am trying to impose a (self-referential) foreign key constraint upon the data to update on cascades and prevent deletion of fruit if they have "children." So I used the following: CREATE TABLE `idtlp_main`.`fruit` ( `id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT, `parent` INT(10) UNSIGNED, `name` VARCHAR(45) NOT NULL, PRIMARY KEY (`id`), CONSTRAINT `fk_parent` FOREIGN KEY (`parent`) REFERENCES `fruit` (`id`) ON UPDATE CASCADE ON DELETE RESTRICT ) ENGINE = InnoDB; From what I understand, this should fit my requirements. (And parent must default to null to allow insertions, correct?) The problem is, if I change the id of a record, it will not cascade: Cannot delete or update a parent row: a foreign key constraint fails (`iddoc_main`.`fruit`, CONSTRAINT `fk_parent` FOREIGN KEY (`parent`) REFERENCES `fruit` (`id`) ON UPDATE CASCADE) What am I missing? Feel free to correct me if my terminology is screwed up... I'm new to constraints.

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  • Combining the UNIQUE and CHECK constraints

    - by Bobby
    I have a table with columns a b and c, and if c is false then I only want to allow insertions if columns a and b are unique, but if c is true then a and b do not need to be unique. Example: There can only be one (foo, bar, false) in the table, but no limit on how many (foo, bar, true) there can be. I tried something like CONSTRAINT blah UNIQUE (a,b) AND CHECK (C is TRUE) but I can't figure out the correct syntax.

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  • integrity Constraints on a table.

    - by Dinesh
    See this sample schema Passenger(id PK, Name) Plane(id PK, capacity, type); Flight(id PK, planeId FK(Plane), flightDate, StartLocation, destination) CREATE TABLE Reservation(PassengerId, flightId, PRIMARY KEY (passengerId, flightId), FOREIGN KEY (passengerId) REFERENCES Passenger, FOREIGN KEY (flightId) REFERENCES Flight); I need to define an integrity constraint that enforces the restriction that the number of passengers on a plane cannot exceed the plane’s capacity. I have tried and achieved so far is this. CREATE TABLE Reservation( passengerId INTEGER, flightId INTEGER, PRIMARY KEY (passengerId, flightId), FOREIGN KEY (passengerId) REFERENCES Passenger, FOREIGN KEY (flightId) REFERENCES Flight, Constraint check1 check(Not Exists(select * from Flight s, (select count(*) as totalRes from Reservation group by flightId) t where t.totalRes > s.capacity ) ) ); I am not sure i am doing in right way or not. Any suggestions?

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