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• Rails uniqueness constraint and matching db unique index for null column

  - by Dave

  I have the following in my migration file def self.up create_table :payment_agreements do |t| t.boolean :automatic, :default => true, :null => false t.string :payment_trigger_on_order t.references :supplier t.references :seller t.references :product t.timestamps end end I want to ensure that if a product_id is specified it is unique but I also want to allow null so I have the following in my model: validates :product_id, :uniqueness => true, :allow_nil => true Works great but I should then add an index to the migration file add_index :payment_agreements, :product_id, :unique => true Obviously this will throw an exception when two null values are inserted for product_id. I could just simply omit the index in the migration but then there's the chance that I'll get two PaymentAgreements with the same product_id as shown here: Concurrency and integrity My question is what is the best/most common way to deal with this problem

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• Converting "is null" into a linq to sql statement

  - by Darryl Braaten

  I am having trouble replicating the following sql as a LINQ statement select TableA.* from TableA left outer join TableAinTableB on TableA.Id = TableAId where TableBId is null The following returns no lines from TableA in db.TableA join AinB in db.TableAinTableB on TableA.Id equals TableAId where AinB.TableBId == null select TableA Also tried and a few other things that didn't work. from TableA in db.TableA join AinB in db.TableAinTableB on TableA.Id equals TableAId where AinB == null select TableA TableAinTableB is a many to many table. The query I want will pull all the records from TableA that have no records in the middle table. My sql does what I want but I have no idea how to convert it to LINQ to SQL. I ended up working around it by just doing a db.ExecuteQuery("working sql"); But I would like to know if the query is possible in LINQ and how to write it, or a pointer to a document that covers this scenario. My searching did not uncover anything I found useful.

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• Graphics.FromHwnd(IntPtr.Zero) returns null, why?

  - by Martin Moser

  I'm currently investigating a problem with a 3rd party component (DevExpress) in my application. My issue is quite similar to this one DevExpress KB article. I get the same exception with more less the same stacktrace. So I used .NET Reflector to find out, what may be null in this scenario, and the only object which is a candiate to be null is Graphics. This is created with Graphics.FromHwnd(IntPtr.Zero). Because I don't have a broad knowledge about GDI, I would like to know if somebody can tell me possible scenarios when this may return null... I tried to reproduce it in a scenario where windows is out of GDI handle's, but then I'm getting a "out of handles" - exception at least once, which is not the case in the issue I'm investigating tia, Martin

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• problem with null column

  - by Iulian

  One column in my database (of type double) has some null values. I am executing a sored procedure to get the data in my app wipDBTableAdapters.XLSFacturiTableAdapter TAFacturi = new wipDBTableAdapters.XLSFacturiTableAdapter(); var dtfacturi = TAFacturi.GetData(CodProiect); Then i try to do something like this: if (dtfacturi[i].CANTITATE == null) { //do something } this is giving a warning : The result of the expression is always 'false' since a value of type 'double' is never equal to 'null' of type 'double? However when i run my code i get the following exception: StrongTypingException The value for column 'CANTITATE' in table 'XLSFacturi' is DBNull. How am I supposed to resolve this ?

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• How to redirect output away from /dev/null

  - by Gowtham

  I have an application that runs the a command as below: <command> >& /dev/null I have no control on this. All the o/p generated by this command goes to /dev/null. I want the output to be visible on screen or redirected to a log file. I tried to use freopen() and related functions to reopen /dev/null to another file, but could not get it working. Do you have any other ideas? Is this possible at all? Thanks for your time. PS: I am working on Linux. -Gowtham

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• JPA getSingleResult() or null

  - by Eugene Ramirez

  Hi. I have an insertOrUpdate method which inserts an Entity when it doesn't exist or update it if it does. To enable this, I have to findByIdAndForeignKey, if it returned null insert if not then update. The problem is how do I check if it exists? So I tried getSingleResult. But it throws an exception if the public Profile findByUserNameAndPropertyName(String userName, String propertyName) { String namedQuery = Profile.class.getSimpleName() + ".findByUserNameAndPropertyName"; Query query = entityManager.createNamedQuery(namedQuery); query.setParameter("name", userName); query.setParameter("propName", propertyName); Object result = query.getSingleResult(); if(result==null)return null; return (Profile)result; } but "getSingleResult" throws an exception. Thanks

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• Object reference error even when object is not null

  - by Shrewd Demon

  hi, i have an application wherein i have incorporate a "Remember Me" feature for the login screen. I do this by creating a cookie when the user logs in for the first time, so next time when the user visits the site i get the cookie and load the user information. i have written the code for loading user information in a common class in the App_Code folder...and all my pages inherit from this class. code for loading the user info is as follows: public static void LoadUserDetails(string emailId) { UsersEnt currentUser = UsersBL.LoadUserInfo(emailId); if (currentUser != null) HttpContext.Current.Session["CurrentUser"] = currentUser; } Now the problem is i get an "Object reference" error when i try to store the currentUser object in the session variable (even though the currentUser object is not null). However the password property in the currentUser object is null. Am i getting the error because of this...or is there some other reason?? thank you

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• ruby on rails group by with null values problem

  - by winter sun

  I have an hour table in witch I store user time tracking information, the table consists from the following cells project_id task_id (optional can be null) worker_id reported_date working_hours each worker enters sevral records per day so generally the table is looking like this id project_id worker_id task_id reported_date working hours; == =========== ========= ========= ============= ============== 1 1 1 1 10/10/2011 4 2 1 1 1 10/10/2011 14 3 1 1 10/10/2011 4 4 1 1 10/10/2011 14 the task_id is not a must field so there can be times when the user is not selecting it and ther task_id cell is empty now i need to display the data by using group by clouse so the resualt will be somthing like this project_id worker_id task_id working hours ========== ========= ========= ============== 1 1 1 18 1 1 18 I did the folowing group by condition @group_hours=Hour.group('project_id,worker_id,task_id)').select('project_id, task_id ,worker_id,sum(working_hours)as working_hours_sum') My view looks like this <% @group_hours.each do |b| % <%= b.project.name if b.project % <%= b.worker.First_name if b.worker % <%= b.task.name if b.task % <%= b.working_hours_sum % <%end% This it is working but only if the task_id is not null when task id is null it present all the records without grouping them like this project_id worker_id task_id working hours =========== ========= ========= ============== 1 1 1 18 1 1 4 1 1 14 I will appreciate any kind of solution to this problem

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• Geolocation Null in lat and long

  - by user1706989

  I have had issue today in one application where Geolocation is not working. Even on this page http://slaveryfootprint.org/survey/#where_do_you_live . When you enter a location , its showing null lattiude and longitude. Even though it search for autolocation, it can point the right location. and it happened all if a sudden today which was working fine since yestrday night and when I see in console it is returning null lat and long and null for city and I did not change the code at all. Did google map api changed something. or do I need to update jquery? http://maps.google.com/maps/api/js?v=3.4&sensor=false

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• linq NullReferenceException while checking for null reference

  - by Odrade

  I have the following LINQ query: List<FileInputItem> inputList = GetInputList(); var results = from FileInputItem f in inputList where ( Path.GetDirectoryName(f.Folder).ToLower().Trim() == somePath || Path.GetDirectoryName(f.Folder).ToLower().Trim() == someOtherPath ) && f.Expression == null select f; Every time this query is executed, it generates a NullReferenceException. If I remove the condition f.Expression == null or change it to f.Expression != null, the query executes normally (giving the wrong results, of course). The relevant bits of FileInputItem look like this: [Serializable] public class FileInputItem { [XmlElement("Folder")] public string Folder { get; set; } [XmlElement("Expression")] public string Expression { get; set; } /*SNIP. Irrelevant properties */ } I'm new to LINQ to objects, so I'm probably missing something fundamental here. What's the deal?

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• flex/actionscript assignment failing?

  - by user346713

  I'm seeing something weird in my actionscript code I have two classes foo and bar, bar extends foo. In a model class I have a foo member variable, I assign an bar object to the foo variable. But after the assignment the foo variable is null. [Bindable] public var f:foo; public function someFunc(arr:ArrayCollection):void { if(arr.length > 0) { var tempBar:bar = arr.getItemAt(0) as bar; if(tempBar != null) { tempBar.someProp++; f = tempBar; // f is now null } } } Any ideas on what I could be doing wrong?

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• Linq To Sql Left outer join - filtering null results

  - by Harry

  I'd like to reproduce the following SQL into C# LinqToSql SELECT TOP(10) Keywords.* FROM Keywords LEFT OUTER JOIN IgnoreWords ON Keywords.WordID = IgnoreWords.ID WHERE (DomainID = 16673) AND (IgnoreWords.Name IS NULL) ORDER BY [Score] DESC The following C# Linq gives the right answer. But I can't help think I'm missing something (a better way of doing it?) var query = (from keyword in context.Keywords join ignore in context.IgnoreWords on keyword.WordID equals ignore.ID into ignored from i in ignored.DefaultIfEmpty() where i == null where keyword.DomainID == ID orderby keyword.Score descending select keyword).Take(10); the SQL produced looks something like this: SELECT TOP (10) [t0].[DomainID], [t0].[WordID], [t0].[Score], [t0].[Count] FROM [dbo].[Keywords] AS [t0] LEFT OUTER JOIN (SELECT 1 AS [test], [t1].[ID] FROM [dbo].[IgnoreWords] AS [t1]) AS [t2] ON [t0].[WordID] = [t2].[ID] WHERE ([t0].[DomainID] = 16673) AND ([t2].[test] IS NULL) ORDER BY [t0].[Score] DESC How can I get rid of this redundant inner selection? It's only slightly more expensive but every bit helps!

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• @OneToOne and @JoinColumn, auto delete null entity , doable?

  - by smallufo

  I have two Entities , with the following JPA annotations : @Entity @Table(name = "Owner") public class Owner implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) @Column(name = "id") private long id; @OneToOne(fetch=FetchType.EAGER , cascade=CascadeType.ALL) @JoinColumn(name="Data_id") private Data Data; } @Entity @Table(name = "Data") public class Data implements Serializable { @Id private long id; } Owner and Data has one-to-one mapping , the owning side is Owner. The problem occurs when I execute : owner.setData(null) ; ownerDao.update(owner) ; The "Owner" table's Data_id becomes null , that's correct. But the "Data" row is not deleted automatically. I have to write another DataDao , and another service layer to wrap the two actions ( ownerDao.update(owner) ; dataDao.delete(data); ) Is it possible to make a data row automatically deleted when the owning Owner set it to null ?

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• concatenating results from SQL query and NULL columns

  - by Curtis

  I need to concatenate several columns of a table into a single value, then show that value in an asp dropdownlist. The SQL code I'm issuing is as follows: SELECT UserID, CustomerNum, UserName + ' - ' + UserAddress + ',' + UserCity + ' ' + UserState AS UserInfo FROM Users WHERE (CustomerNum = @CustomerNum) ORDER BY UserName I then set 'UserInfo' as the text field in the dropdownlist. This generally works, except occasionally one of the columns in the database is null (for example, UserState). When that happens, the entire concatenation is null, and I get an empty entry in the dropdownlist. Is there something in SQLServer that will allow me to ignore those NULL results, or will I have to code something up in the DataBind event? Thanks

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• nullable type and a ReSharper warning

  - by Sarah Vessels

  I have the following code: private static LogLevel? _logLevel = null; public static LogLevel LogLevel { get { if (!_logLevel.HasValue) { _logLevel = readLogLevelFromFile(); } return _logLevel.Value; } } private static LogLevel readLogLevelFromFile() { ... } I get a ReSharper warning on the return statement about a possible System.InvalidOperationException and it suggests I check _logLevel to see if it is null first. However, readLogLevelFromFile returns LogLevel, not LogLevel?, so there is no way the return statement could be reached when _logLevel is null. Is this just an oversight by ReSharper, or am I missing something?

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• IEnumerable not null but calling Count() results in Exception

  - by Draak

  I have code that's working beautifully on my development machine, but when deployed to the server is throwing null reference exception. So, I can't step through the code, but I've pinned down the culprit. But now I am puzzled. Here's the code. The question is below. Dim certs = From p In persons _ Select New Certificate( _ p.Value, _ New CertificateData.Seminar(thisEvent.Seminar.Name, _ thisEvent.StartDate.Value, _ thisEvent.EndDate.Value, _ thisEvent.Venue.City, _ thisEvent.Venue.State, _ New CertificateData.Instructor( _ staffMember.Name, _ staffMember.Titles, _ instrSignatPath))) _ With {.CertificateId = p.Key} lblMessage.Text = CStr(certs Is Nothing) lblMessage.Text = lblMessage.Text + "<br />" + CStr(certs.Count()) In the code above persons is a dictionary of custom class, and certs is of IEnumerable type. Now here's the quandary.. The first line that sets the label returns False, so certs is not null. But the second line throws an null reference exception. How is this possible?

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• When can argv[0] have null ?

  - by andrew-dufresne

  What I have understand about passing arguments to main() from command line is that argc has a minimum value of 1 and argv[0] will always have the program name with its path in it. If arguments are provided at the command line, then argc will have a value greater than one and argv1 to argv[argc-1] will have those arguments. Now a paragraph at this link says that argv[0] will be a string containing the program's name or a null string if that is not available. Now, how and when can argv[0] have null string? I mean program name with its path will always be available so when can it be null? Writer says that "if that is not available" but when and how it is possible that program name will not be available? Thanks for your time and support. Regards

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• (this == null) in C#!

  - by SLaks

  Due to a bug that was fixed in C# 4, the following program prints true. (Try it in LINQPad) void Main() { new Derived(); } class Base { public Base(Func<string> valueMaker) { Console.WriteLine(valueMaker()); } } class Derived : Base { string CheckNull() { return "Am I null? " + (this == null); } public Derived() : base(() => CheckNull()) { } } In VS2008 in Release mode, in throws an InvalidProgramException. (In Debug mode, it works fine) In VS2010 Beta 2, it doesn't compile (I didn't try Beta 1); I learned that the hard way Is there any other way to make this == null in pure C#?

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• Nested for loop error with !null checking an element that doesn't exist

  - by Programatt

  I am currently using nested for loops in a 2D array of size 4,2. When I run my program, I get index out of bounds Exception on the following line else if (state[i][j+1] != null && state[i][j].getFlash() <= state[i][j].getCycleLength() && state[i][j+1].getCycleLength() == state[i][j].getCycleLength()){ } It says the index out of bounds is 2. I would understand the error if I wasn't checking to see if [i][j+1] wasn't null, but I don't understand the exception with the check? I tried moving around the !null check but the program still fails on this line. Any help would be greatly appreciated. Stack trace: Exception in thread "Timer-0" java.lang.ArrayIndexOutOfBoundsException: 2 at NatComp.data$1.run(data.java:67) at java.util.TimerThread.mainLoop(Timer.java:512) at java.util.TimerThread.run(Timer.java:462)

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• typeof === "undefined" vs. != null

  - by Thor Thurn

  I often see JavaScript code which checks for undefined parameters etc. this way: if (typeof input !== "undefined") { // do stuff } This seems kind of wasteful, since it involves both a type lookup and a string comparison, not to mention its verbosity. It's needed because 'undefined' could be renamed, though. My question is: How is that code any better than this approach: if (input != null) { // do stuff } As far as I know, you can't redefine null, so it's not going to break unexpectedly. And, because of the type-coercion of the != operator, this checks for both undefined and null... which is often exactly what you want (e.g. for optional function parameters). Yet this form does not seem widespread, and it even causes JSLint to yell at you for using the evil != operator. Why is this considered bad style?

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• C# Events and Lambdas, alternative to null check?

  - by Eugarps

  Does anybody see any drawbacks? It should be noted that you can't remove anonymous methods from an event delegate list, I'm aware of that (actually that was the conceptual motivation for this). The goal here is an alternative to: if (onFoo != null) onFoo.Invoke(this, null); And the code: public delegate void FooDelegate(object sender, EventArgs e); public class EventTest { public EventTest() { onFoo += (p,q) => { }; } public FireFoo() { onFoo.Invoke(this, null); } public event FooDelegate onFoo; }

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• JSP doPost getAtribute null value

  - by newbie123

  I want to pass value to servlet but I keep get null value. <jsp:useBean id="Helper" class="model.Registration" scope="request"/> <form action="/Project/Registration" method="post" enctype="multipart/form-data"> <input type="text" size="20" name="name" value="<%=Helper.getName()%>"> <input type="submit"> </form> protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { Registrationh2 = (Registration) request.getAttribute("Helper"); if(h2!=null){ System. out.println(h2.getName()); } else System. out.println("NULL"); } Is there anything wrong with my code?

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• routing paramenter returns null when only supplying first paramenter in MVC

  - by Ray ForRespect

  My issue is that I customer Map Route in MVC which takes three parameters. When I supply all three or just two, the parameters are passed from the URL to my controller. However, when I only supply the first parameter, it is not passed and returns null. Not sure what causes this behavior. Route: routes.MapRoute( name: "Details", // Route name url: "{controller}/{action}/{param1}/{param2}/{param3}", // URL with parameters defaults: new { controller = "Details", action = "Index", param1 = UrlParameter.Optional, param2 = UrlParameter.Optional, param3 = UrlParameter.Optional } // Parameter defaults ); Controller: public ActionResult Map(string param1, string param2, string param3) { StoreMap makeMap = new StoreMap(); var storemap = makeMap.makeStoreMap(param1, param2, param3); var model = storemap; return View(model); } string param1 returns null when I navigate to: /StoreMap/Map/PARAM1NAME but it doesn't return null when I navigate to: /StoreMap/Map/PARAM1NAME/PARAM2NAME

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• Cannot output json from MySQL - getting null value

  - by sky

  I'm using following code but cannot return data from MySQL. This is the output: <script type="text/javascript"> var somethings= [null,null,null]; </script> It does have three post, but I couldn't get the title(message) output. EDIT: this is the code I'm using: <?php $session = mysql_connect('localhost','name','pass'); mysql_select_db('dbname', $session); $result= mysql_query('SELECT * FROM posts', $session); $somethings= array(); while ($row= mysql_fetch_assoc($result)) { $somethings[]= $row['something']; } ?> <script type="text/javascript"> var somethings= <?php echo json_encode($somethings); ?>; </script>

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• MVVM Binding To Property == Null

  - by LnDCobra

  I want to show some elements when a property is not null. What is the best way of achieving this? The following is my ViewModel: class ViewModel : ViewModelBase { public Trade Trade { get { return _trade; } set { SetField(ref _trade, value, () => Trade); } } private Trade _trade; } ViewModelBase inherits INotifyPropertyChanged and contains SetField() The Following is the Trade class: public class Trade : INotifyPropertyChaged { public virtual Company Company { get { return _company; } set { SetField(ref _company, value, () => Company); } } private Company _company; ...... } This is part of my View.xaml <GroupBox Visibility="{Binding Path=Trade.Company, Converter={StaticResource boolToVisConverter}}" /> I would like this groupbox to show only if Trade.Company is not null (so when a user selects a company). Would I need to create a custom converter to check for null and return the correct visibility or is there one in .NET?

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