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• Rails - inheritance hierarchy of classes where a subtype can play two roles

  - by Miquel

  I need to model Owners and Rentees in an application, so you have stuff that is always owned by someone and can be rented for someone else. I first approached this problem with Single Table Inheritance because both types of person will share all attributes, so you would have a model called Person associated to a table people with Owner and Rentee inheriting from Person. The problem is that Single type inheritance discerns subtypes using a field type and therefore a record in the table can represent either an Owner or a Rentee but not both at the same time, while in the real context you can have an Owner which is renting something from another Owner and therefore that person is at the same time an Owner and a Rentee. How would you approach this problem? Would you use separated tables for owners and rentees? Is there any other type of table inheritance in Rails?

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• Disallow typing of few of characters e.g.'<', '>' in all input textboxes using jquery

  - by Ismail

  How do I achieve this:- When user types character like 'abcd' and then '>'(an invalid character for my application), I want to set the text back to 'abcd'. Better if we can cancel the input itself as we do in winforms application. This should happen when user is typing and not on a click of button. I want this to be applied on all text boxes in my web page. This will be easy if the solution is jQuery based. May be something which will start like this. $("input[type='text']")

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• How to ensure consistency of enums in Java serialization?

  - by Uri

  When I serialize an object, I can use the serialVersionUID mechanism at the class level to ensure the compatibility of the two types. However, what happens when I serialize fields of enum values? Is there a way to ensure that the enum type has not been manipulated between serialization and deserialization? Suppose that I have an enum like OperationResult {SUCCESS, FAIL}, and a field called "result" in an object that is being serialized. How do I ensure, when the object is deserialized, that result is still correct even if someone maliciously reversed the two? (Suppose the enum is declared elsewhere as a static enum) I am wondering out of curiosity - I use jar-level authentication to prevent manipulation.

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• best way to write a-> ..->[a] recursive functions in haskell

  - by Roman A. Taycher

  So I keep having this small problem where I have something like func :: a -> b -> [a] -- or basically any a-> ...-> [a] where ... is any types -> func x y = func' [x] y -- as long as they are used to generate a list of [a] from x func' :: [a] -> b -> [a] func = undefined --situation dependant generates a list from each element and returns it as one long list should I keep it like this? should I use func' hidden by a where? should I only use the [a] - b - [a] version and leave the responsibility of passing [variable] to the callee? I might well need to compose these functions and might want to mess around with the order so I'm leaning towards option 3. What do you think?

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• aspectRatio = backingWidth / backingHeight ???

  - by carrots

  What am I doing wrong here, I can't get the result of this division: aspectRatio = backingWidth / backingHeight; I've thought I might try casting to (GLfloat) but that didn't do anything. As I step through the code I see that aspectRatio is 0 after the operation, while backingWidth is clearly 768 and backingHeight is 1029. Here are the types: GLfloat aspectRatio; and // The pixel dimensions of the CAEAGLLayer GLint backingWidth; GLint backingHeight; It must be something basic I'm doing wrong here..

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• How to call split(token) on a string that does not contain the token without causing an error?

  - by Vorinowsky

  I have two types of strings as the IDs of elements in my HTML markup: Dates: "april-23" "march-20" and season names: "springtime" "winter" The dates have a dash separating the month and the day. The seasons are a single word with no other tokens. I want to assign the month or the season to a new variable called: time_of_year If I do this: var time_of_year = $(this).attr("id").split('-')[0]; It will work on the months but if I call it on a season name which does not contain the token, will it generate an error? What's the safe way to do this?

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• Recordset Update errors when updating sql_variant field

  - by Stephen Nutt

  I'm using C++ and ADO to add data to a SQL Server 2005 database. When calling the Recordset Update method for a sql_variant column I'm getting the error DB_E_ERRORSOCCURRED and the error message Multiple-step OLE DB operation generated errors. Check each OLE DB status value, if available. No work was done. If the value I'm adding is NULL all works fine and all values going to the fields that are not sql_variant types work. Does anyone know what I might be doing wrong? Thanks [Edit] I have some more information. The value we are storing is the empty string - ADO appears to want to store this in the sql_variant as a nchar(0), which of course is not a valid SQL data type. Is there a way to get an empty string in a sql_variant using the ADO batch commands?

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• Why does the assignment operator return a value and not a reference?

  - by Nick Lowman

  I saw the example below explained on this site and thought both answers would be 20 and not the 10 that is returned. He wrote that both the comma and assignment returns a value, not a reference. I don't quite understand what that means. I understand it in relation to passing variables into functions or methods i.e primitive types are passed in by value and objects by reference but I'm not sure how it applies in this case. I also understand about context and the value of 'this' (after help from stackoverflow) but I thought in both cases I would still be invoking it as a method, foo.bar() which would mean foo is the context but it seems both result in a function call bar(). Why is that and what does it all mean? var x = 10; var foo = { x: 20, bar: function () {return this.x;} }; (foo.bar = foo.bar)();//returns 10 (foo.bar, foo.bar)();//returns 10

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• C++ enforce conditions on inherited classes

  - by user231536

  I would like to define an abstract base class X and enforce the following: a) every concrete class Y that inherits from X define a constructor Y(int x) b) it should be possible to test whether two Y objects are equal. For a, one not very good solution is to put a pure virtual fromInt method in X which concrete class will have to define. But I cannot enforce construction. For b), I cannot seem to use a pure virtual method in X bool operator == (const X& other) const =0; because in overridden classes this remains undefined. It is not enough to define bool operator == (const Y& other) const { //stuff} because the types don't match. How do I solve these problems?

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• What is the best signature for overloaded arithmetic operators in C++?

  - by JohnMcG

  I had assumed that the canonical form for operator+, assuming the existence of an overloaded operator+= member function, was like this: const T operator+(const T& lhs, const T& rhs) { return T(lhs) +=rhs; } But it was pointed out to me that this would also work: const T operator+ (T lhs, const T& rhs) { return lhs+=rhs; } In essence, this form transfers creation of the temporary from the body of the implementation to the function call. It seems a little awkward to have different types for the two parameters, but is there anything wrong with the second form? Is there a reason to prefer one over the other?

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• How do I print the method body reflectively?

  - by kunjaan

  Right now I have private static void getMethods(Class<? extends Object> clazz) { Method[] declaredMethods = clazz.getDeclaredMethods(); for (Method aMethod : declaredMethods) { aMethod.setAccessible(true); // Print the declaration System.out.print(Modifier.toString(aMethod.getModifiers()) + " " + aMethod.getReturnType().getSimpleName() + " " + aMethod.getName()); // Get Parameter Types getParameters(aMethod); //Empty Body System.out.println("{}\n"); } } Which prints most information reflectively but creates an empty body. How do I add to the reflective nature of Java to print the method body?

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• Using Multiple Databases

  - by sergiuoala

  A company is hired by another company for helping in a certain field. So I created the following tables: Companies: id, company name, company address Administrators: (in relation with companies) id, company_id, username, email, password, fullname Then, each company has some workers in it, I store data about workers. Hence, workers has a profession, Agreement Type signed and some other common things. Now, the parent tables and data in it for workers (Agreement Types, Professions, Other Common Things) are going to be the same for each company. Should I create 1 new database for each company? Or store All data into the same database? Thanks.

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• ASP.Net website makes browser load unwanted (non-referenced) plugins

  - by alec0001

  I've found that some of my ASP.Net web apps prompt the browser to load plugins that I'm not explicitely using and certainly haven't deliberately referenced in the project settings. Two that come to mind are for MS MediaPlayer and the "SVG Viewer for Netscape". The only commonality I've determined so far is that the two sites/apps affected both use Master pages (nested in some cases). We don't use SVG file types (just the normal mix of jpg/gif/png) and no video/audio (not yet anyway). Can anyone provide a hint as to where the references for these might be creeping in? e.g. Is it a server-level include? Or a .Net runtime default when using master pages? Does anyone else even experience this, or is it just me? No urgency, I'd just like to remove it if possible. Thanks. Al

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• Flex: How to create a floating notification message of sorts for a custom component?

  - by aberrant80

  I have a custom TextInput-based component for date and time with certain restrictions on what's considered "within range". But it's still fine to insert dates that are outside the range. When a user types in a date, on valueCommit, I'd like to be able to display a hovering notification to the user, to inform/warn them that the date is outside the accepted range. I'm thinking of notifications ala the Validators, but I'd rather not use the Validator mechanism because it's really not validation, just notification. Something like a tooltip, but it will only appear if the user changed the value. Maybe an effect of some sort? If anyone has any ideas or if anyone has done something like this, I'm all ears!

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• Optimal way to initialize varying objects

  - by John Smith

  I have to initialize a lot of different types of objects based on an integer parameter. They all have the same overall initialization methods. At the moment I have the following code #def APPLE 1 #def PEAR 2 switch (t) { case APPLE: newobj = [[FApple alloc] init]; break; case PEAR: newobj = [[FPear] alloc] init]; break; default: retobj = nil; } I believe there must be a better way to do this. When I add FOrange I have to go and add another line here. What would be a better way?

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• ASP.net: Efficient ways to convert DataSets to GenericCollection (Of ObjectType)

  - by jlrolin

  I currently have a function that gets some data from the database and puts it into a dataset. The return type on my function is GenericCollection (Of CustomerDetails) If I do this: Dim dataset As DataSet = Read(strSQL.ToString) 'Gets Data from DB What's the most efficient way to map the dataset results to an collection of objects. More importantly, since I'm using GenericCollection, is there a way to do this in which I can call a function from the ObjectType class (CustomerDetails) that would have a means to converting that specific object. Or is there a way in which I can use a function that would handle all types? Is there a way to do something like: Return returnedResults.TransformDataSet(dataset) In which returnedResults is an object collection Of CustomerDetails, or would it simply be easier to have TransformDataSet return an object collection Of CustomerDetails by itself? Thanks for any help.

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• Create an Action<T> to "set" a property, when I am provided with the LINQ Expression for the "get"

  - by Alex

  I'd like to be able to generate a compiled expression to set a property, given the lambda expression that provides the "get" method for a property. Here's what I'm looking for: public Action<int> CreateSetter<T>(Expression<Func<T, int>> getter) { // returns a compiled action using the details of the getter expression tree, or null // if the write property is not defined. } I'm still trying to understand the various types of Expression classes, so if you can point me in the right direction that would be great.

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• How do I remove a control if not a specific type?

  - by joek1975

  I have a control that I need to restrict the types of child controls that it can contain during design time (dragging a new control onto an existing control on the form designer). I tried to do this by overriding the OnControlAdded event: Protected Overrides Sub OnControlAdded(ByVal e As System.Windows.Forms.ControlEventArgs) MyBase.OnControlAdded(e) If e.Control.GetType() IsNot GetType(ExpandablePanel) Then MsgBox("You can only add the ExpandablePanel control to the TaskPane.", MsgBoxStyle.Exclamation Or MsgBoxStyle.OkOnly, "TaskPane") Controls.Remove(e.Control) End If End Sub This seems to work, however I get an error message from Visual Studio immediately after the control is removed: 'child' is not a child control of this parent. What does this mean? How can I accomplish this without errors occurring?

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• No mapping for LONGVARCHAR in Hibernate 3.2

  - by jimbokun

  I am running Hibernate 3.2.0 with MySQL 5.1. After updating the group_concat_max_len in MySQL (because of a group_concat query that was exceeding the default value), I got the following exception when executing a SQLQuery with a group_concat clause: "No Dialect mapping for JDBC type: -1" -1 is the java.sql.Types value for LONGVARCHAR. Evidently, increasing the group_concat_max_len value causes calls to group_concat to return a LONGVARCHAR value. This appears to be an instance of this bug: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3892 I guess there is a fix for this issue in Hibernate 3.5, but that is still a development version, so I am hesitant to put it into production, and don't know if it would cause issues for other parts of my code base. I could also just use JDBC queries, but then I have to replace every instance of a SQLQuery with a group_concat clause. Any other suggestions?

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• Does this make any sense (Apple-documentation)?

  - by Paperflyer

  Here is a snippet of the official Apple Documentation of AudioBufferList (Core Audio Data Types Reference) AudioBufferList Holds a variable length array of AudioBuffer structures. struct AudioBufferList { UInt32 mNumberBuffers; AudioBuffer mBuffers[1]; }; typedef struct AudioBufferList AudioBufferList; Fields mNumberBuffers The number of AudioBuffer structures in the mBuffers array. mBuffers A variable length array of AudioBuffer structures. If mBuffers is defined as AudioBuffer[1] it is not of variable length and thus mNumberBuffers is implicitly defined as 1. Do I miss something here or is this just nonsense?

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• Setting variable to value of form [drupal 6]

  - by N Schleder

  I have this form $form['title'] = array( '#type' => 'textfield', '#title' => t('Title of Notice'), '#description' => t('Use_underscores_as_spaces'), '#size' => 30, // '#required' => TRUE ); and I want whatever the user types in to be the value of $test I've tried $test = $form['title']; which gives me $test = array also I've tried $test = current($form['title']); which gives me $test = textfield $form['values']['title'] doesn't work dont know what else to try

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• VB.NET Abstract Property

  - by ElPresidente

  I have an abstract "GridBase" class with two types of derived classes "DetailGrid" and "HeaderGrid". Respectively, one is comprised of "DetailRow" objects and the other "HeaderRow" objects. Both of those inherit from a "RowBase" abstract class. What I am trying to do is the following: Public MustInherit Class GridBase Private pRows As List(Of RowBase) Public ReadOnly Property Rows As List(Of RowBase) Get Return pRows End Get End Property End Class Public Class DetailGrid Inherits GridBase End Class In this scenario, I want DetailGrid.Rows to return a list of DetailRow. I want HeaderRow.Rows to return a list of HeaderRow. Am I on the right track with this or should the Rows property not be included in the GridBase class?

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• How can an SQL query return data from multiple tables

  - by Fluffeh

  I would like to know how to get data from multiple tables in my database, what types of methods are there to do this, what are joins and unions and how are they different from one another? When should I use each one compared to the others? I am planning to use this in my (for example - PHP) application, but don't want to run multiple queries against the database, what options do I have to get data from multiple tables in a single query? Note: I am writing this as I would like to be able to link to a well written guide on the numerous questions that I constantly come across in the PHP queue, so I can link to this for further detail when I post an answer. The answers cover off the following: Part 1 - Joins and Unions Part 2 - Subqueries Part 3 - Tricks and Efficient Code

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• Javascript Inheritance and Arrays

  - by Inespe

  Hi all! I am trying to define a javascript class with an array property, and its subclass. The problem is that all instances of the subclass somehow "share" the array property: // class Test function Test() { this.array = []; this.number = 0; } Test.prototype.push = function() { this.array.push('hello'); this.number = 100; } // class Test2 : Test function Test2() { } Test2.prototype = new Test(); var a = new Test2(); a.push(); // push 'hello' into a.array var b = new Test2(); alert(b.number); // b.number is 0 - that's OK alert(b.array); // but b.array is containing 'hello' instead of being empty. why? As you can see I don't have this problem with primitive data types... Any suggestions?

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• How does ‘Servers’ view work underlying in Eclipse?

  - by Michael Lu

  ‘Servers’ is built-in view in Eclipse. We could integrate jee server into Eclipse easily. It could start/stop server both in normal and debug modes. Moreover, we could even set timeout and deployment path, things like that. Various types of server tomcat, jboss, websphere are supported, no intrusive to server. I am just curious about how these cool things happen behind the scene. The complete mechanism is large and complex, so I just want to know general mechanism about it, an article also could be fine for me. Thank you!

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