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  • Active Record two belongs_to calls or single table inheritance

    - by ethyreal
    In linking a sports event to two teams, at first this seemed to make sense: events - id:integer - integer:home_team_id - integer:away_team_id teams - integer:id - string:name However I am troubled by how I would link that up in the active record model: class Event belongs_to :home_team, :class_name => 'Team', :foreign_key => "home_team_id" belongs_to :away_team, :class_name => 'Team', :foreign_key => "away_team_id" end Is that the best solution? In an answer to a similar question I was pointed to single table inheritance, and then later found polymorphic associations. Neither of which seemed to fit this association. Perhaps I am looking at this wrong, but I see no need to subclass a team into home and away teams since the distinction is only in where the game is played. If I did go with single table inheritance I wouldn't want each team to belong_to an event so would this work? # app/models/event.rb class Event < ActiveRecord::Base belongs_to :home_team belongs_to :away_team end # app/models/team.rb class Team < ActiveRecord::Base has_many :teams end # app/models/home_team.rb class HomeTeam < Team end # app/models/away_team.rb class AwayTeam < Team end I thought also about a has_many through association but that seems two much as I will only ever need two teams, but those two teams don't belong to any one event. event_teams - integer:event_id - integer:team_id - boolean:is_home Is there a cleaner more semantic way for making these associations in active record? or is one of these solutions the best choice? Thanks

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  • Inheritance of closure objects and overriding of methods

    - by bobikk
    I need to extend a class, which is encapsulated in a closure. This base class is following: var PageController = (function(){ // private static variable var _current_view; return function(request, new_view) { ... // priveleged public function, which has access to the _current_view this.execute = function() { alert("PageController::execute"); } } })(); Inheritance is realised using the following function: function extend(subClass, superClass){ var F = function(){ }; F.prototype = superClass.prototype; subClass.prototype = new F(); subClass.prototype.constructor = subClass; subClass.superclass = superClass.prototype; StartController.cache = ''; if (superClass.prototype.constructor == Object.prototype.constructor) { superClass.prototype.constructor = superClass; } } I subclass the PageController: var StartController = function(request){ // calling the constructor of the super class StartController.superclass.constructor.call(this, request, 'start-view'); } // extending the objects extend(StartController, PageController); // overriding the PageController::execute StartController.prototype.execute = function() { alert('StartController::execute'); } Inheritance is working. I can call every PageController's method from StartController's instance. However, method overriding doesn't work: var startCont = new StartController(); startCont.execute(); alerts "PageController::execute". How should I override this method?

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  • @PrePersist with entity inheritance

    - by gerry
    I'm having some problems with inheritance and the @PrePersist annotation. My source code looks like the following: _the 'base' class with the annotated updateDates() method: @javax.persistence.Entity @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS) public class Base implements Serializable{ ... @Id @GeneratedValue protected Long id; ... @Column(nullable=false) @Temporal(TemporalType.TIMESTAMP) private Date creationDate; @Column(nullable=false) @Temporal(TemporalType.TIMESTAMP) private Date lastModificationDate; ... public Date getCreationDate() { return creationDate; } public void setCreationDate(Date creationDate) { this.creationDate = creationDate; } public Date getLastModificationDate() { return lastModificationDate; } public void setLastModificationDate(Date lastModificationDate) { this.lastModificationDate = lastModificationDate; } ... @PrePersist protected void updateDates() { if (creationDate == null) { creationDate = new Date(); } lastModificationDate = new Date(); } } _ now the 'Child' class that should inherit all methods "and annotations" from the base class: @javax.persistence.Entity @NamedQueries({ @NamedQuery(name=Sensor.QUERY_FIND_ALL, query="SELECT s FROM Sensor s") }) public class Sensor extends Entity { ... // additional attributes @Column(nullable=false) protected String value; ... // additional getters, setters ... } If I store/persist instances of the Base class to the database, everything works fine. The dates are getting updated. But now, if I want to persist a child instance, the database throws the following exception: MySQLIntegrityConstraintViolationException: Column 'CREATIONDATE' cannot be null So, in my opinion, this is caused because in Child the method "@PrePersist protected void updateDates()" is not called/invoked before persisting the instances to the database. What is wrong with my code?

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  • Programming exercises in Java inheritance for intern

    - by Tenner
    I work for a small software development team, working primarily in Java, for a very large company. Our new intern showed up sight-unseen (not uncommon in my company). He has some C++ experience but no Java. Worse, he's never worked with inheritance in C++. Our code has a great deal of abstraction and a heavy reliance on inheritance. We need to get him up to speed as quickly as possible. Of course the rest of the team is busy, and so we can't take the time out of our day to teach a one-student 200-level CS course. Instead, I'd like to give him an actual programming project to work on which highlights how classes, interfaces, method overrides, etc. work. I've had him look at Project Euler, but most of the solutions end up being procedural, and not object-oriented programs. Do any of you have any somewhat-straightforward (and relatively quick) projects which you would give to an intern in this situation? Or, any recent (or current) students have a school project they'd be willing to share? Anyone else had this experience?

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  • Rails Model inheritance in forms

    - by Tiago
    I'm doing a reporting system for my app. I created a model ReportKind for example, but as I can report a lot of stuff, I wanted to make different groups of report kinds. Since they share a lot of behavior, I'm trying to use inheritance. So I have the main model: model ReportKind << ActiveRecord::Base end and created for example: model UserReportKind << ReportKind end In my table report_kinds I've the type column, and until here its all working. My problem is in the forms/controllers. When I do a ReportKind.new, my form is build with the '*report_kind*' prefix. If a get a UserReportKind, even through a ReportKind.find, the form will build the 'user_report_kind' prefix. This mess everything in the controllers, since sometimes I'll have params[:report_kind], sometimes params[:user_report_kind], and so on for every other inheritance I made. Is there anyway to force it to aways use the 'report_kind' prefix? Also I had to force the attribute 'type' in the controller, because it didn't get the value direct from the form, is there a pretty way to do this? Routing was another problem, since it was trying to build routes based in the inherited models names. I overcome that by adding the other models in routes pointing to the same controller.

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  • Asp.net mvc inheritance controllers

    - by Ris90
    Hi, I'm studing asp.net mvc and in my test project I have some problems with inheritance: In my model I use inheritanse in few entities: public class Employee:Entity { /* few public properties */ } It is the base class. And descendants: public class RecruitmentOfficeEmployee: Employee { public virtual RecruitmentOffice AssignedOnRecruitmentOffice { get; set; } } public class ResearchInstituteEmployee: Employee { public virtual ResearchInstitute AssignedOnResearchInstitute { get; set; } } I want to implement a simple CRUD operations to every descedant. What is the better way to inplement controllers and views in descendants: - One controller per every descendant; - Controller inheritance; - Generic controller; - Generic methods in one controller. Or maybe there is an another way? My ORM is NHibernate, I have a generic base repository and every repository is its descedant. Using generic controller, I think, is the best way, but in it I will use only generic base repository and extensibility of the system will be not very good. Please, help the newbie)

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  • Problem understanding Inheritance

    - by dhruvbird
    I've been racking my brains over inheritance for a while now, but am still not completely able to get around it. For example, the other day I was thinking about relating an Infallible Human and a Fallible Human. Let's first define the two: Infallible Human: A human that can never make a mistake. It's do_task() method will never throw an exception Fallible Human: A human that will occasionally make a mistakes. It's do_task() method may occasionally throw a ErrorProcessingRequest Exception The question was: IS an infallible human A fallible human OR IS a fallible human AN infallible human? The very nice answer I received was in the form of a question (I love these since it gives me rules to answer future questions I may have). "Can you pass an infallible human where a fallible human is expected OR can you pass a fallible human where an infallible human is expected?" It seems apparent that you can pass an infallible human where a fallible human is expected, but not the other way around. I guess that answered my question. However, it still feels funny saying "An infallible human is a fallible human". Does anyone else feel queasy when they say it? It almost feels as if speaking out inheritance trees is like reading out statements from propositional calculus in plain English (the if/then implication connectives don't mean the same as that in spoken English). Does anyone else feel the same?

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  • template pass by const reference

    - by 7vies
    Hi, I've looked over a few similar questions, but I'm still confused. I'm trying to figure out how to explicitly (not by compiler optimization etc) and C++03-compatible avoid copying of an object when passing it to a template function. Here is my test code: #include <iostream> using namespace std; struct C { C() { cout << "C()" << endl; } C(const C&) { cout << "C(C)" << endl; } ~C() { cout << "~C()" << endl; } }; template<class T> void f(T) { cout << "f<T>" << endl; } template<> void f(C c) { cout << "f<C>" << endl; } // (1) template<> void f(const C& c) { cout << "f<C&>" << endl; } // (2) int main() { C c; f(c); return 0; } (1) accepts the object of type C, and makes a copy. Here is the output: C() C(C) f<C> ~C() ~C() So I've tried to specialize with a const C& parameter (2) to avoid this, but this simply doesn't work (apparently the reason is explained in this question). Well, I could "pass by pointer", but that's kind of ugly. So is there some trick that would allow to do that somehow nicely? EDIT: Oh, probably I wasn't clear. I already have a templated function template<class T> void f(T) {...} But now I want to specialize this function to accept a const& to another object: template<> void f(const SpecificObject&) {...} But it only gets called if I define it as template<> void f(SpecificObject) {...}

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  • Why C# does not support multiple inheritance?

    - by Jalpesh P. Vadgama
    Yesterday, One of my friend Dharmendra ask me that why C# does not support multiple inheritance. This is question most of the people ask every time. So I thought it will be good to write a blog post about it. So why it does not support multiple inheritance? I tried to dig into the problem and I have found the some of good links from C# team from Microsoft for why it’s not supported in it. Following is a link for it. http://blogs.msdn.com/b/csharpfaq/archive/2004/03/07/85562.aspx Also, I was giving some of the example to my friend Dharmendra where multiple inheritance can be a problem.The problem is called the diamond problem. Let me explain a bit. If you have class that is inherited from the more then one classes and If two classes have same signature function then for child class object, It is impossible to call specific parent class method. Here is the link that explains more about diamond problem. http://en.wikipedia.org/wiki/Diamond_problem Now of some of people could ask me then why its supporting same implementation with the interfaces. But for interface you can call that method explicitly that this is the method for the first interface and this the method for second interface. This is not possible with multiple inheritance. Following is a example how we can implement the multiple interface to a class and call the explicit method for particular interface. Multiple Inheritance in C# That’s it. Hope you like it. Stay tuned for more update..Till then happy programming.

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  • Javascript Inheritance Part 2

    - by PhubarBaz
    A while back I wrote about Javascript inheritance, trying to figure out the best and easiest way to do it (http://geekswithblogs.net/PhubarBaz/archive/2010/07/08/javascript-inheritance.aspx). That was 2 years ago and I've learned a lot since then. But only recently have I decided to just leave classical inheritance behind and embrace prototypal inheritance. For most of us, we were trained in classical inheritance, using class hierarchies in a typed language. Unfortunately Javascript doesn't follow that model. It is both classless and typeless, which is hard to fathom for someone who's been using classes the last 20 years. For the last two or three years since I've got into Javascript I've been trying to find the best way to force it into the class model without much success. It's clunky and verbose and hard to understand. I think my biggest problem was that it felt so wrong to add or change object members at run time. Every time I did it I felt like I needed a shower. That's the 20 years of classical inheritance in me. Finally I decided to embrace change and do something different. I decided to use the factory pattern to build objects instead of trying to use inheritance. Javascript was made for the factory pattern because of the way you can construct objects at runtime. In the factory pattern you have a factory function that you call and tell it to give you a certain type of object back. The factory function takes care of constructing the object to your specification. Here's an example. Say we want to have some shape objects and they have common attributes like id and area that we want to depend on in other parts of your application. So first thing to do is create a factory object and give it a factory method to create an abstract shape object. The factory method builds the object then returns it. var shapeFactory = { getShape: function(id){ var shape = { id: id, area: function() { throw "Not implemented"; } }; return shape; }}; Now we can add another factory method to get a rectangle. It calls the getShape() method first and then adds an implementation to it. getRectangle: function(id, width, height){ var rect = this.getShape(id); rect.width = width; rect.height = height; rect.area = function() { return this.width * this.height; }; return rect;} That's pretty simple right? No worrying about hooking up prototypes and calling base constructors or any of that crap I used to do. Now let's create a factory method to get a cuboid (rectangular cube). The cuboid object will extend the rectangle object. To get the area we will call into the base object's area method and then multiply that by the depth. getCuboid: function(id, width, height, depth){ var cuboid = this.getRectangle(id, width, height); cuboid.depth = depth; var baseArea = cuboid.area; cuboid.area = function() { var a = baseArea.call(this); return a * this.depth; } return cuboid;} See how we called the area method in the base object? First we save it off in a variable then we implement our own area method and use call() to call the base function. For me this is a lot cleaner and easier than trying to emulate class hierarchies in Javascript.

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  • How does a template class inherit another template class?

    - by hkBattousai
    I have a "SquareMatrix" template class which inherits "Matrix" template class, like below: SquareMatrix.h: #ifndef SQUAREMATRIX_H #define SQUAREMATRIX_H #include "Matrix.h" template <class T> class SquareMatrix : public Matrix<T> { public: T GetDeterminant(); }; template <class T> // line 49 T SquareMatrix<T>::GetDeterminant() { T t = 0; // Error: Identifier "T" is undefined // line 52 return t; // Error: Expected a declaration // line 53 } // Error: Expected a declaration // line 54 #endif I commented out all other lines, the files contents are exactly as above. I receive these error messages: LINE 49: IntelliSense: expected a declaration LINE 52: IntelliSense: expected a declaration LINE 53: IntelliSense: expected a declaration LINE 54: error C2039: 'GetDeterminant' : is not a member of 'SquareMatrix' LINE 54: IntelliSense: expected a declaration So, what is the correct way of inheriting a template class? And what is wrong with this code? The "Matrix" class: template <class T> class Matrix { public: Matrix(uint64_t unNumRows = 0, uint64_t unNumCols = 0); void GetDimensions(uint64_t & unNumRows, uint64_t & unNumCols) const; std::pair<uint64_t, uint64_t> GetDimensions() const; void SetDimensions(uint64_t unNumRows, uint64_t unNumCols); void SetDimensions(std::pair<uint64_t, uint64_t> Dimensions); uint64_t GetRowSize(); uint64_t GetColSize(); void SetElement(T dbElement, uint64_t unRow, uint64_t unCol); T & GetElement(uint64_t unRow, uint64_t unCol); //Matrix operator=(const Matrix & rhs); // Compiler generate this automatically Matrix operator+(const Matrix & rhs) const; Matrix operator-(const Matrix & rhs) const; Matrix operator*(const Matrix & rhs) const; Matrix & operator+=(const Matrix & rhs); Matrix & operator-=(const Matrix & rhs); Matrix & operator*=(const Matrix & rhs); T& operator()(uint64_t unRow, uint64_t unCol); const T& operator()(uint64_t unRow, uint64_t unCol) const; static Matrix Transpose (const Matrix & matrix); static Matrix Multiply (const Matrix & LeftMatrix, const Matrix & RightMatrix); static Matrix Add (const Matrix & LeftMatrix, const Matrix & RightMatrix); static Matrix Subtract (const Matrix & LeftMatrix, const Matrix & RightMatrix); static Matrix Negate (const Matrix & matrix); // TO DO: static bool IsNull(const Matrix & matrix); static bool IsSquare(const Matrix & matrix); static bool IsFullRowRank(const Matrix & matrix); static bool IsFullColRank(const Matrix & matrix); // TO DO: static uint64_t GetRowRank(const Matrix & matrix); static uint64_t GetColRank(const Matrix & matrix); protected: std::vector<T> TheMatrix; uint64_t m_unRowSize; uint64_t m_unColSize; bool DoesElementExist(uint64_t unRow, uint64_t unCol); };

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  • tfs 2010 RC Agile Process template update New Task progress report

    Maybe my next post will just be about why I am so excited and impressed with the out of the box templates.  But, for this first blog with my new focus, I thought I would just walk through the process I went through to create a task progress report (to enhance the out of the box Agile template). So, I started with the MSF for Agile Development 5.0 RC template.  After reviewing the template, I came away pretty excited about many of the new reports.  I am especially excited about the reporting services reports.  The big advantage I see here is that these are querying the Warehouse directly instead of the Analysis Services Cube which means that they are much closer to real-time which I find very important for reports like Burndown and task status.  One report that I focused on right away was the User Story Progress Report.  An overview is shown below: This report is very useful, but a lot of our internal managers really prefer to manage at the task level and either dont have stories in TFS or would like to view this type of report for tasks in addition to the User Stories.  So, what did I do? Step 1: Download the Agile Template In VS 2010 RC, open Process Template Manager from Team->Team Project Collection Settings.  Download the MSF for Agile Development template to your local file system.  A project template is a folder of xml files.  There is a ProcessTemplate.xml in the root and then a bunch of directories for things like Work Item Definitions and Queries, Reports, Shared Documents and Source Control Settings.  Step 2: Copy the folder My plan here is to make a new template with all of my modifications.  You can also just enhance update the MSF template.  However, I think it is cleaner when you start making modifications to make your own template.  So, copy the folder and name it with your new template name. Step 3: Change Template Name Open ProcessTemplate.xml and change the <name> of the template. Step 4: Copy the rdl of the Report you want to use a starting point In my case, I copied Stories Progress.rdl and named the file Task Progress Breakdown.rdl.  I reviewed the requirements for the new report with some of the users here and came up with this plan.  Should show tasks and be expandable to show subtasks.  Should add Assigned To and Estimated Finish Date as 2 extra columns. Step 5: Walkthrough the existing report to understand how it works The main thing that I do here is try to get the sql to run in SQL Management Studio.  So, I can walkthrough the process of building up the data for the report. After analyzing this particular report I found a couple of very useful things.  One, this report is already built to display subtasks if I just flip the IncludeTasks flag to 1.  So, if you are using Stories and have tasks assigned to each story.  This might give you everything you want.  For my purposes, I did make that change to the Stories Progress report as I find it to be a more useful report to be able to see the tasks that comprise each story.  But, I still wanted a task only version with the additional fields. Step 6: Update the report definition I tend to work on rdl in visual studio directly as xml.  Especially when I am just altering an existing report, I find it easier than trying to deal with the BI Studio designer.  For my report I made the following changes. Updated Fields Removed Stack Rank and Replaced with Priority since we dont use Stack Rank Added FinishDate and AssignedTo Changed the root deliverable SQL to pull @tasks instead of @deliverablecategory and added a join CurrentWorkItemView for FinishDate and Assigned to SELECT cwi.[System_Id] AS ID FROM [CurrentWorkItemView] cwi             WHERE cwi.[System_WorkItemType] IN (@Task)             AND cwi.[ProjectNodeGUID] = @ProjectGuid SELECT lh.SourceWorkItemID AS ID FROM FactWorkItemLinkHistory lh             INNER JOIN [CurrentWorkItemView] cwi ON lh.TargetWorkItemID = cwi.[System_Id]             WHERE lh.WorkItemLinkTypeSK = @ParentWorkItemLinkTypeSK                 AND lh.RemovedDate = CONVERT(DATETIME, '9999', 126)                 AND lh.TeamProjectCollectionSK = @TeamProjectCollectionSK                 AND cwi.[System_WorkItemType] NOT IN (@DeliverableCategory) Added AssignedTo and FinishDate columns to the @Rollups table Added two columns to the table used for column headers <Tablix Name="ProgressTable">         <TablixBody>           <TablixColumns>             <TablixColumn>               <Width>2.7625in</Width>             </TablixColumn>             <TablixColumn>               <Width>0.5125in</Width>             </TablixColumn>             <TablixColumn>               <Width>3.4625in</Width>             </TablixColumn>             <TablixColumn>               <Width>0.7625in</Width>             </TablixColumn>             <TablixColumn>               <Width>1.25in</Width>             </TablixColumn>             <TablixColumn>               <Width>1.25in</Width>             </TablixColumn>           </TablixColumns> Added Cells for the two new headers Added Cells to the data table to include the two new values (Assigned to & Finish Date) Changed a bunch of widths that would change the format of the report to display landscape and have room for the two additional columns Set the Value of the IncludeTasks Parameter to 1 <ReportParameter Name="IncludeTasks">       <DataType>Integer</DataType>       <DefaultValue>         <Values>           <Value>=1</Value>         </Values>       </DefaultValue>       <Prompt>IncludeTasks</Prompt>       <Hidden>true</Hidden>     </ReportParameter> Change a few descriptions on how the report should be used This is the resulting report I have attached the final rdl. Step 7: Update ReportTasks.xml Last step before the template is ready for use is to update the reportTasks.xml file in the reports folder.  This file defines the reports that are available in the template.           <report name="Task Progress Breakdown" filename="Reports\Task Progress Breakdown.rdl" folder="Project Management" cacheExpiration="30">             <parameters>               <parameter name="ExplicitProject" value="" />             </parameters>             <datasources>               <reference name="/Tfs2010ReportDS" dsname="TfsReportDS" />             </datasources>           </report> Step 8: Upload the template Open the process Template Manager just like Step 1.  And upload the new template. Thats it.  One other note, if you want to add this report to existing team project you will have to go into reportmanager (the reporting services portal) and upload the rdl to that projects directory.Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • problem with template inheritance

    - by amiad
    I'm trying to understand whay i get an error on this code: (the error is under g++ unix compiler. VS is compiling OK) template<class T> class A { public: T t; public: A(const T& t1) : t(t1) {} virtual void Print() const { cout<<*this<<endl;} friend ostream& operator<<(ostream& out, const A<T>& a) { out<<"I'm "<<typeid(a).name()<<endl; out<<"I hold "<<typeid(a.t).name()<<endl; out<<"The inner value is: "<<a.t<<endl; return out; } }; template<class T> class B : public A<T> { public: B(const T& t1) : A<T>(t1) {} const T& get() const { return t; } }; int main() { A<int> a(9); a.Print(); B<A<int> > b(a); b.Print(); (b.get()).Print(); return 0; } This code is giving the following error: main.cpp: In member function 'const T& B::get() const': main.cpp:23: error: 't' was not declared in this scope It did compiled when i changed the code of B to this: template<class T> class B : public A<T> { public: B(const T& t1) : A<T>(t1) {} const T& get() const { return A<T>::t; } }; I just cant understand what is the problem with the first code... It doesn't make sense that i really need to write "A::" every time...

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  • WPF Window Inheritance

    - by Jonathan Sternberg
    I have an application that will run in two modes, each with very similar displays. The application is supposed to allow easy modification of a user interface. One of the features is that it has to display the user interface. Both of these windows look the same, just one has more menus than the other. I'd like to just create a base template (the user visual) and then inherit it for the editor. That way if one interface changes, both of them change. But this doesn't seem to be possible using WPF. I try to inherit and I get warnings about hiding members. I also don't see how I'm going to append new menus to the base template. Is what I'm trying to do possible? Is there a better way that I'm supposed to be doing this? It seems like I'm fighting the way that they want me to make the application.

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  • Documenting PHP multiple inheritance with PhpDoc

    - by Sam Dark
    I have multiple inheritance like this one: http://stackoverflow.com/questions/356128/can-i-extend-a-class-using-more-than-1-class-in-php (let's not discuss this approach itself please) and want my IDE to know about inherited class methods and properties. Is there a way to do it with PhpDoc?

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  • Django Multi-Table Inheritance VS Specifying Explicit OneToOne Relationship in Models

    - by chefsmart
    Hope all this makes sense :) I'll clarify via comments if necessary. Also, I am experimenting using bold text in this question, and will edit it out if I (or you) find it distracting. With that out of the way... Using django.contrib.auth gives us User and Group, among other useful things that I can't do without (like basic messaging). In my app I have several different types of users. A user can be of only one type. That would easily be handled by groups, with a little extra care. However, these different users are related to each other in hierarchies / relationships. Let's take a look at these users: - Principals - "top level" users Administrators - each administrator reports to a Principal Coordinators - each coordinator reports to an Administrator Apart from these there are other user types that are not directly related, but may get related later on. For example, "Company" is another type of user, and can have various "Products", and products may be supervised by a "Coordinator". "Buyer" is another kind of user that may buy products. Now all these users have various other attributes, some of which are common to all types of users and some of which are distinct only to one user type. For example, all types of users have to have an address. On the other hand, only the Principal user belongs to a "BranchOffice". Another point, which was stated above, is that a User can only ever be of one type. The app also needs to keep track of who created and/or modified Principals, Administrators, Coordinators, Companies, Products etc. (So that's two more links to the User model.) In this scenario, is it a good idea to use Django's multi-table inheritance as follows: - from django.contrib.auth.models import User class Principal(User): # # # branchoffice = models.ForeignKey(BranchOffice) landline = models.CharField(blank=True, max_length=20) mobile = models.CharField(blank=True, max_length=20) created_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalcreator") modified_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalmodifier") # # # Or should I go about doing it like this: - class Principal(models.Model): # # # user = models.OneToOneField(User, blank=True) branchoffice = models.ForeignKey(BranchOffice) landline = models.CharField(blank=True, max_length=20) mobile = models.CharField(blank=True, max_length=20) created_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalcreator") modified_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalmodifier") # # # Please keep in mind that there are other user types that are related via foreign keys, for example: - class Administrator(models.Model): # # # principal = models.ForeignKey(Principal, help_text="The supervising principal for this Administrator") user = models.OneToOneField(User, blank=True) province = models.ForeignKey( Province) landline = models.CharField(blank=True, max_length=20) mobile = models.CharField(blank=True, max_length=20) created_by = models.ForeignKey(User, editable=False, blank=True, related_name="administratorcreator") modified_by = models.ForeignKey(User, editable=False, blank=True, related_name="administratormodifier") I am aware that Django does use a one-to-one relationship for multi-table inheritance behind the scenes. I am just not qualified enough to decide which is a more sound approach.

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  • multiple class inheritance

    - by redcoder
    In PHP, is it possible to have multiple inheritance (by the nature of the PHP, not writting modification code) ? example : class a { public function foo(); } class b { public function bar(); } class c extends a, b { public function baz(); }

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  • Using inheritance in PostgreSQL

    - by Anton Prokofiev
    Hello, All! Is somebody have an experience using inheritance in PostgreSQL? Is it worth to use it, or better to keep hands of :)? In which situation you would use it? To be true I'm a little bit in doubt about mixing relational and OO models...

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  • How to prevent inheritance for some methods?!

    - by Dr TJ
    Hi How can I prevent inheritance of some methods or properties in derived classes?! public class BaseClass : Collection { //Some operations... //Should not let derived classes inherit 'Add' method. } public class DerivedClass : BaseClass { public void DoSomething(int Item) { this.Add(Item); // Error: No such method should exist... } }

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  • Reducing template bloat with inheritance

    - by benoitj
    Does anyone have experience reducing template code bloat using inheritance? i hesitate rewriting our containers this way: class vectorBase { public: int size(); void clear(); int m_size; void *m_rawData; //.... }; template< typename T > class vector : public vectorBase { void push_back( const T& ); //... }; I should keep maximum performance while reducing compile time I'm also wondering why stl implementations do not uses this approach Thanks for your feedbacks

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  • Problem persisting inheritance tree

    - by alaiseca
    I have a problem trying to map an inheritance tree. A simplified version of my model is like this: @MappedSuperclass @Embeddable public class BaseEmbedded implements Serializable { @Column(name="BE_FIELD") private String beField; // Getters and setters follow } @MappedSuperclass @Embeddable public class DerivedEmbedded extends BaseEmbedded { @Column(name="DE_FIELD") private String deField; // Getters and setters follow } @MappedSuperclass public abstract class BaseClass implements Serializable { @Embedded protected BaseEmbedded embedded; public BaseClass() { this.embedded = new BaseEmbedded(); } // Getters and setters follow } @Entity @Table(name="MYTABLE") @Inheritance(strategy=InheritanceType.SINGLE_TABLE) @DiscriminatorColumn(name="TYPE", discriminatorType=DiscriminatorType.STRING) public class DerivedClass extends BaseClass { @Id @Column(name="ID", nullable=false) private Long id; @Column(name="TYPE", nullable=false, insertable=false, updatable=false) private String type; public DerivedClass() { this.embedded = new DerivedClass(); } // Getters and setters follow } @Entity @DiscriminatorValue("A") public class DerivedClassA extends DerivedClass { @Embeddable public static NestedClassA extends DerivedEmbedded { @Column(name="FIELD_CLASS_A") private String fieldClassA; } public DerivedClassA() { this.embedded = new NestedClassA(); } // Getters and setters follow } @Entity @DiscriminatorValue("B") public class DerivedClassB extends DerivedClass { @Embeddable public static NestedClassB extends DerivedEmbedded { @Column(name="FIELD_CLASS_B") private String fieldClassB; } public DerivedClassB() { this.embedded = new NestedClassB(); } // Getters and setters follow } At Java level, this model is working fine, and I believe is the appropriate one. My problem comes up when it's time to persist an object. At runtime, I can create an object which could be an instance of DerivedClass, DerivedClassA or DerivedClassB. As you can see, each one of the derived classes introduces a new field which only makes sense for that specific derived class. All the classes share the same physical table in the database. If I persist an object of type DerivedClass, I expect fields BE_FIELD, DE_FIELD, ID and TYPE to be persisted with their values and the remaining fields to be null. If I persist an object of type DerivedClass A, I expect those same fields plus the FIELD_CLASS_A field to be persisted with their values and field FIELD_CLASS_B to be null. Something equivalent for an object of type DerivedClassB. Since the @Embedded annotation is at the BaseClass only, Hibernate is only persisting the fields up to that level in the tree. I don't know how to tell Hibernate that I want to persist up to the appropriate level in the tree, depending on the actual type of the embedded property. I cannot have another @Embedded property in the subclasses since this would duplicate data that is already present in the superclass and would also break the Java model. I cannot declare the embedded property to be of a more specific type either, since it's only at runtime when the actual object is created and I don't have a single branch in the hierarchy. Is it possible to solve my problem? Or should I resignate myself to accept that there is no way to persist the Java model as it is? Any help will be greatly appreciated.

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  • Inheritance question / problem

    - by Itsik
    I'm creating a custom Layout for android. The layout implementation is exactly the same, but once I need to extend from RelativeLayout, and once from LinearLayout. class Layout1 extends LinearLayout { // methods and fields } class Layout2 extends RelativeLayout { // the same EXACT methods and fields } How can I use inheritance to avoid DRY and implement my methods once.

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