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• hibernate modeling relationships managed through an intermediate table

  - by shikarishambu

  I have a datamodel that has an intermediate table to manage relationships between entities. For example, tables Person and Organization are related through the Relationship table Party (table) - ID Person (table) - ID (references Party.ID) - name Organization (table) -ID (references Party.ID) -name Relationship (table) -ID (PK) -type (references relationshiptype lookup) -fromID (references Party.ID) -ToID (references Party.ID) -fromDate -ToDate Type+fromID+ToID+fromDate+ToDate is guaranteed to be unique. How do I manage this using hibernate? TIA

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• Is it OK to manage associations manually?

  - by sosborn

  Here are the relevant models: User Product Order A User can sell or buy products An order has a buyer, a seller and one product I know that I can do this with a HABTM relationship between orders and user, but is seems to me like it would be simpler to put in the Order table the following columns: :seller_id :buyer_id and manage those relationships manually as orders are only created once and never edited. However, this doesn't seem very Rails-like and I am wondering if I am missing something conceptually at the HABTM relationship.

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• When does the DENY delete rule in Core Data actually deny deletion of an object?

  - by dontWatchMyProfile

  An Employee has an inverse relationship to it's Department and vice versa. The Employee entity has an Relationship called department, and it has a DENY delete rule. Employee shall be deleted. Now: Does DENY actually deny deletion of employee, because department is still referencing a Department? Or does it mean that a Department can't be deleted because an Employee is referencing it?

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• What exactly is the Nullify delete rule doing?

  - by dontWatchMyProfile

  Does that mean that if I delete an managed object which has references (relationship) to some others, the relationships are removed to those others? Example: objectA references objectB and objectC. objectA gets deleted, it's relationship to objectB and objectC is set to the Nullify rule. What happens in detail?

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• Accessing Values of a ForeignKey or OneToOne object in ModelForm

  - by theactiveactor

  I have a ModelFormA for ModelA, which has a one-one relationship with ModelB and foreign-key relationship with ModelC. Inside ModelFormA, I can access attributes of the current ModelA instance via self.cleaned_data["colA-1"]. How would I access attributes of ModelB or ModelC?

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• Declare Locally or Globally in Delphi?

  - by lkessler

  I have a procedure my program calls tens of thousands of times that uses a generic structure like this: procedure PrintIndiEntry(JumpID: string); type TPeopleIncluded = record IndiPtr: pointer; Relationship: string; end; var PeopleIncluded: TList<TPeopleIncluded>; PI: TPeopleIncluded; begin { PrintIndiEntry } PeopleIncluded := TList<TPeopleIncluded>.Create; { A loop here that determines a small number (up to 100) people to process } while ... do begin PI.IndiPtr := ...; PI.Relationship := ...; PeopleIncluded.Add(PI); end; DoSomeProcess(PeopleIncluded); PeopleIncluded.Clear; PeopleIncluded.Free; end { PrintIndiEntry } Alternatively, I can declare PeopleIncluded globally rather than locally as follows: unit process; interface type TPeopleIncluded = record IndiPtr: pointer; Relationship: string; end; var PeopleIncluded: TList<TPeopleIncluded>; PI: TPeopleIncluded; procedure PrintIndiEntry(JumpID: string); begin { PrintIndiEntry } { A loop here that determines a small number (up to 100) people to process } while ... do begin PI.IndiPtr := ...; PI.Relationship := ...; PeopleIncluded.Add(PI); end; DoSomeProcess(PeopleIncluded); PeopleIncluded.Clear; end { PrintIndiEntry } procedure InitializeProcessing; begin PeopleIncluded := TList<TPeopleIncluded>.Create; end; procedure FinalizeProcessing; begin PeopleIncluded.Free; end; My question is whether in this situation it is better to declare PeopleIncluded globally rather than locally. I know the theory is to define locally whenever possible, but I would like to know if there are any issues to worry about with regards to doing tens of thousands of of "create"s and "free"s? Making them global will do only one create and one free. What is the recommended method to use in this case? If the recommended method is to still define it locally, then I'm wondering if there are any situations where it is better to define globally when defining locally is still an option.

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• How can I move deleting photos to the background with delayed_job and paperclip

  - by Tam

  I let my users create photo albums with many photos. Relationship as follows: has_many :album_photos, :dependent => :destroy i upload photos to S3 When the user delete album I want to delete all photos as the relationship shows but it takes time if the user has many photos. Can I automatically set photo deletion to happen in the background (delayed_job) without having to manually call 'send_later' on every photo?

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• Linqbuilder Query with an OrderBy

  - by Renshai

  I have a 1 : M relationship. I built a dynamic query based on input from users to return the listing of parents entities along with their children (using predicate builder: (done successfully new TDataContext().Ps.Where(predicate) )... but need to order the results by a field found only on the child entities. I'm at a loss: new TDataContext().Ps.Where(predicate).OrderBy(p = p.Cs. ??) where Ps = parents collection relationship with Cs = child entities any help appreciated.

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• Can someone help me with two-entity coreData iOS6?

  - by user1878923

  I'm new in iOS development and i need simple example (project) with explained two-entity coreData with to-many relationship between A and B entities on iOS6 with storyboard interface and ARC. In storyboard should be two UITableView controllers which present entities A and B and two UIViewControllers which present adding string data from text fields I searched in many books, sites, video lessons like "lynda.com", but i still not understand how and where i should implement two-entity coredata with one to-many relationship in code. Can someone give me link to understandable tutorial or put the project on GitHub?

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• Casting To The Correct Subclass

  - by kap

  Hi Guys I hava a supeclass called Car with 3 subclasses. class Ford extends Car{ } class Chevrolet extends Car{ } class Audi extends Car{ } Now i have a function called printMessge(Car car) which will print a message of a particular car type. In the implementation i use if statements to test the instance of the classes like this. public int printMessge(Car car){ if((Ford)car instanceof Ford){ // print ford }else if((Chevrolet)car instanceof Chevrolet){ // print chevrolet }else if((Audi)car instanceof Audi){ // print Audi } } for instance if i call it for the first time with Ford printMessge(new Ford()), it prints the ford message but when i call it with printMessge(new Chevrolet()), i get EXCEPTION from the first if statement that Chevrolet cannot be cast to Ford. What am i doing wrong and what is the best way. thanks

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• How to access "overridden" inner class in Scala?

  - by doom2.wad

  I have two traits, one extending the other, each with an inner class, one extending the other, with the same names: trait A { class X { def x() = doSomething() } } trait B extends A { class X extends super.X { override def x() = doSomethingElse() } } class C extends B { val x = new X() // here B.X is instantiated val y = new A.X() // does not compile val z = new A.this.X() // does not compile } How do I access A.X class in the C class's body? Renaming B.X not to hide A.X is not a preferred way. To make things a bit complicated, in the situation I have encountered this problem the traits have type parameters (not shown in this example).

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• C# to Java: where T : new() Syntax

  - by Shiftbit

  I am porting some C# code over to Java. I am having trouble with the where Syntax, specifically new(). I understand that where is similar to Java's generic: T extends FOO. How I can replicate the new() argument in Java? "The new() Constraint lets the compiler know that any type argument supplied must have an accessible parameterless--or default-- constructor." - MSDN ie: public class BAR<T> : BAR where T : FOO, new() Right now I have: public class BAR<T extends FOO> extends ABSTRACTBAR { public HXIT(T t){ this.value = t; } .... }

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• Java, filling arrays, and inheritance

  - by Arvanem

  Hi folks, I think I'm running into an inheritance conceptual wall with my Java arrays. I'm kind of new to Java so please tell me if I have things upside down. In essence, I want to do three things: Create a runnersArray with the attributes of my Runners class. Fill my runnersArray using my GenerateObjects method of my GenerateObjects class. Access the contents of my filled runnersArray in my Evaluating method of my Evaluating class. The problem seems to be that runnersArray is not visible to the methods in steps 2 and 3 above, but their classes (due to design reasons) cannot inherit or extend Runners class. Thanks in advance for any suggestions. Here are some code snippets showing what I'm trying to do: public class Runners extends Party { Runners[] runnersArray = new Runners[5]; } and public class GenerateObject extends /* certain parent class */ { public GenerateObject (int arrayNum) { runnersArray[arrayNum] = /* certain Runners attributes */; } } and public class Evaluating extends /*certain parent class*/ { public Evaluating (int arrayNum) { System.out.println(/* String cast attribute of runnersArray[arrayNum]*/; } }

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• JPA : Inheritance - Discriminator value not taken into account in generated SQL

  - by Julien

  I try to use this mapping : @Entity @Table(name="ecc.\"RATE\"") @Inheritance(strategy=InheritanceType.SINGLE_TABLE) @DiscriminatorColumn(name="DISCRIMINATOR", discriminatorType= DiscriminatorType.STRING) public abstract class Rate extends GenericBusinessObject { ... } @Entity @DiscriminatorValue("E") public class EntranceRate extends Rate { @ManyToOne @JoinColumn(name = "\"RATES_GRID_ID\"") protected RatesGrid ratesGrid; ... } @Entity @Table(name="ecc.\"RATES_GRID\"") public class RatesGrid extends GenericBusinessObject { /** */ @OneToMany(mappedBy = "ratesGrid", targetEntity = EntranceRate.class, fetch=FetchType.LAZY) private List<EntranceRate> entranceRates; } When I try to access my entranceRates list from a ratesGrid object, I get this error : Object with id: 151 was not of the specified subclass: com.ecc.bo.rate.EntranceRate (loaded object was of wrong class class com.ecc.bo.rate.AnnualRate) Looking at the sql generated, I found no trace of "discriminator=" in the where clause. What am I doing wrong ? I use a PostGreSQL database and a Hibernate as JPA provider.

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• How to generate Doctrine models/classes that extend a custom record class

  - by Shane O'Grady

  When I use Doctrine to generate classes from Yaml/db each Base class (which includes the table definition) extends the Doctrine_Record class. Since my app uses a master and (multiple) slave db servers I need to be able to make the Base classes extend my custom record class to force writes to go to the master db server (as described here). However if I change the base class manually I lose it again when I regenerate my classes from Yaml/db using Doctrine. I need to find a way of telling Doctrine to extend my own Base class, or find a different solution to a master/slave db setup using Doctrine. Example generated model: abstract class My_Base_User extends Doctrine_Record { However I need it to be automatically generated as: abstract class My_Base_User extends My_Record { I am using Doctrine 1.2.1 in a new Zend Framework 1.9.6 application if it makes any difference.

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• Equivalent of public static final fields in Scala

  - by JT

  I'm learning Scala, and I can't figure out how to best express this simple Java class in Scala: public class Color { public static final Color BLACK = new Color(0, 0, 0); public static final Color WHITE = new Color(255, 255, 255); public static final Color GREEN = new Color(0, 0, 255); private static final int red; private static final int blue; private static final int green; public Color(int red, int blue, int green) { this.red = red; this.blue = blue; this.green = green; } // getters, et cetera } The best I have is the following: class Color(val red: Int, val blue: Int, val green: Int) object BLACK extends Color(0, 0, 0) object WHITE extends Color(255, 255, 255) object GREEN extends Color(0, 0, 255) But I lose the advantages of having BLACK, WHITE, and GREEN being tied to the Color namespace.

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• how can I implement Comparable more than once?

  - by codeman73

  I'm upgrading some code to Java 5 and am clearly not understanding something with Generics. I have other classes which implement Comparable once, which I've been able to implement. But now I've got a class which, due to inheritance, ends up trying to implement Comparable for 2 types. Here's my situation: I've got the following classes/interfaces: interface Foo extends Comparable<Foo> interface Bar extends Comparable<Bar> abstract class BarDescription implements Bar class FooBar extends BarDescription implements Foo With this, I get the error 'interface Comparable cannot be implemented more than once with different arguments...' Why can't I have a compareTo(Foo foo) implemented in FooBar, and also a compareTo(Bar) implemented in BarDescription? Isn't this simply method overloading?

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• how to register a selectionProvider for the Viewer from a superclass

  - by Tom

  I have a View which extends a View provided by another plugin like this; public class View2 extends some.other.package.View1 { public void createPartControl(Composite parent) { super.createPartControl(parent); //I want to do this, but I can't because its private //getSite().setSelectionProvider(treeViewer); } } But I can't edit the super class, so I need to access the viewer from the Control. public class some.other.package.View1 extends ViewPart { private TreeViewer treeViewer; public void createPartControl(Composite parent) { treeViewer = new TreeViewer(parent, SWT.V_SCROLL); } } I tried using parent.getChildren(); to get a Tree object, but I can't see that it can be cooerced into an ISElectionProvider as required

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• Java generics SuppressWarnings("unchecked") mystery

  - by Johannes Ernst

  Why does code alternative(1) compile without warnings, and code alternative(2) produce an "unchecked cast" warning? Common for both: class Foo<T> { Foo( T [] arg ) { } } Alternative (1): class Bar<T> extends Foo<T> { protected static final Object [] EMPTY_ARRAY = {}; @SuppressWarnings("unchecked") Bar() { super( (T []) EMPTY_ARRAY ); } } Alternative (2): class Bar<T> extends Foo<T> { @SuppressWarnings("unchecked") Bar() { super( (T []) EMPTY_ARRAY ); } protected static final Object [] EMPTY_ARRAY = {}; } Alternative (2) produces: javac -Xlint:unchecked Foo.java Bar.java Bar.java:4: warning: [unchecked] unchecked cast super( (T []) EMPTY_ARRAY ); ^ required: T[] found: Object[] where T is a type-variable: T extends Object declared in class Bar 1 warning This is: java version "1.7.0_07" Java(TM) SE Runtime Environment (build 1.7.0_07-b10) Java HotSpot(TM) 64-Bit Server VM (build 23.3-b01, mixed mode)

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• Signature of Collections.min/max method

  - by Marco

  In Java, the Collections class contains the following method: public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> c) Its signature is well-known for its advanced use of generics, so much that it is mentioned in the Java in a Nutshell book and in the official Sun Generics Tutorial. However, I could not find a convincing answer to the following question: Why is the formal parameter of type Collection<? extends T>, rather than Collection<T>? What's the added benefit?

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• Workaround for abstract attributes in Java

  - by deamon

  In Scala I would write an abstract class with an abstract attribute path: abstract class Base { val path: String } class Sub extends Base { override val path = "/demo/" } Java doesn't know abstract attributes and I wonder what would be the best way to work around this limitation. My ideas: a) constructor parameter abstract class Base { protected String path; protected Base(String path) { this.path = path; } } class Sub extends Base { public Sub() { super("/demo/"); } } b) abstract method abstract class Base { // could be an interface too abstract String getPath(); } class Sub extends Base { public String getPath() { return "/demo/"; } } Which one do you like better? Other ideas? I tend to use the constructor since the path value should not be computed at runtime.

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• Android; Confused by views?

  - by javano

  I have created a class (InputControl) which extends the view of my main class (Main), and takes focus of the screen. I have a button on the main xml layout which calls control() and sets up my InputControl view, from there I capture user input. How can I return back to the xml layout from the InputControl view class? public class Main extends Activity { public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); InputControl = new InputControl(this); } //......SNIP! public void control(){ setContentView(InputControl); InputControl.requestFocus(); } } public class InputControl extends View implements OnTouchListener { public InputControl(Context context) { super(context); setFocusable(true); setFocusableInTouchMode(true); this.setOnTouchListener(this); } public boolean onTouch(View view, MotionEvent event) { //...I AM CAPTURING USER TOUCH EVENTS HERE } }

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• Implicit parameter in Scalaz

  - by Thomas Jung

  I try to find out why the call Ø in scalaz.ListW.<^> works def <^>[B: Zero](f: NonEmptyList[A] => B): B = value match { case Nil => Ø case h :: t => f(Scalaz.nel(h, t)) } My minimal theory is: trait X[T]{ def y : T } object X{ implicit object IntX extends X[Int]{ def y = 42 } implicit object StringX extends X[String]{ def y = "y" } } trait Xs{ def ys[T](implicit x : X[T]) = x.y } class A extends Xs{ def z[B](implicit x : X[B]) : B = ys //the call Ø } Which produces: import X._ scala> new A().z[Int] res0: Int = 42 scala> new A().z[String] res1: String = y Is this valid? Can I achieve the same result with fewer steps?

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• Inheritance in XML Schema definition (XSD) for Java objects

  - by bguiz

  Hi, I need to create an XML schema definition (XSD) that describes Java objects. I was wondering how to do this when the objects in question inherit from a common base class with a type parameter. public abstract class Rule<T> { ... } public abstract class TimeRule extends Rule<XTime> { ... } public abstract class LocationRule extends Rule<Location> { ... } public abstract class IntRule extends Rule<Integer> { ... } .... (where XTime and Location are custom classes define elsewhere) How would I go about constructing an XSD that such that I can have XML nodes that represent each of the subclasses of Rule<T> - without the XSD for each of them repeating their common contents? Thank you!

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• Example of contravariance

  - by Misha

  I am thinking of the following example to illustrate why contravariance is useful. Let's consider a GUI framework with Widgets, Events, and Event Listeners. abstract class Event; class KeyEvent extends Event class MouseEvent extends Event trait EventListener[-Event] { def listen(e:Event) } Let Widgets define the following methods: def addKeyEventListener(listener:EventListener[KeyEvent]) def addMouseEventListener(listener:EventListener[MouseEvent]) These methods accept only "specific" event listeners, which is fine. However I would like to define also "kitchen-sink" listeners, which listen to all events, and pass such listeners to the "add listener" methods above. For instance, I would like to define LogEventListener to log all incoming events class LogEventListener extends EventListener[Event] { def listen(e:Event) { log(event) } } Since the trait EventListener is contravariant in Event we can pass LogEventListener to all those "add listener" methods without losing their type safety. Does it make sense ?

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