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  • inheritance in document database?

    - by nils petersohn
    i am wondering because i searched the pdf "xxx the definitive guide" and "beginning xxx" for the word "inheritance" but i didn't find anything? am i missing something? because i am doing a tablePerHierarchy inheritance with hibernate and mysql, does that become deprecated for some reason in xxx? (replace xxx with the "not only sql" database you like)

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  • Naming methods that do the same thing but return different types

    - by Konstantin Ð.
    Let's assume that I'm extending a graphical file chooser class (JFileChooser). This class has methods which display the file chooser dialog and return a status signature in the form of an int: APPROVE_OPTION if the user selects a file and hits Open /Save, CANCEL_OPTION if the user hits Cancel, and ERROR_OPTION if something goes wrong. These methods are called showDialog(). I find this cumbersome, so I decide to make another method that returns a File object: in the case of APPROVE_OPTION, it returns the file selected by the user; otherwise, it returns null. This is where I run into a problem: would it be okay for me to keep the showDialog() name, even though methods with that name — and a different return type — already exist? To top it off, my method takes an additional parameter: a File which denotes in which directory the file chooser should start. My question to you: Is it okay to call a method the same name as a superclass method if they return different types? Or would that be confusing to API users? (If so, what other name could I use?) Alternatively, should I keep the name and change the return type so it matches that of the other methods? public int showDialog(Component parent, String approveButtonText) // Superclass method public File showDialog(Component parent, File location) // My method

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  • Why does Java allow to implement different interfaces, each containing a method with the same signature?

    - by Software Engeneering Learner
    I've recently found that I can have two interfaces containing method with the same signature as a method in the other interface. And then I can have an interface or class that implements both of that interfaces. So the descendant class/interface has implicitly implements two different methods as a one method. Why is this allowed in Java? I can see a numerous problems that arises from that. Even eclipse only can find out about implementations for only one interface method, but for the second one it doesn't show any implementations at all. Also I believe there would be problems with automatic refactoring, like when you would like to change the signature of the method in one of the interfaces and IDE won't be able to correctly change that signature in all implementations, as they implement two different interfaces and how will IDE know what interface method it implementation descends. Why don't just make a compiler error like 'interfaces method names clashes' or something like that?

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  • Matching the superclass's constructor's parameter list, is treating a null default value as a non-null value within a constructor a violation of LSP?

    - by Panzercrisis
    I kind of ran into this when messing around with FlashPunk, and I'm going to use it as an example. Essentially the main sprite class is pretty much class Entity. Entity's constructor has four parameters, each with a default value. One of them is graphic, whose default value is null. Entity is designed to be inherited from, with many such subclasses providing their own graphic within their own internal workings. Normally these subclasses would not have graphic in their constructor's parameter lists, but would simply pick something internally and go with it. However I was looking into possibly still adhering to the Liskov Substitution Principal. Which led me to the following example: package com.blank.graphics { import net.flashpunk.*; import net.flashpunk.graphics.Image; public class SpaceGraphic extends Entity { [Embed(source = "../../../../../../assets/spaces/blank.png")] private const BLANK_SPACE:Class; public function SpaceGraphic(x:Number = 0, y:Number = 0, graphic:Graphic = null, mask:Mask = null) { super(x, y, graphic, mask); if (!graphic) { this.graphic = new Image(BLANK_SPACE); } } } } Alright, so now there's a parameter list in the constructor that perfectly matches the one in the super class's constructor. But if the default value for graphic is used, it'll exhibit two different behaviors, depending on whether you're using the subclass or the superclass. In the superclass, there won't be a graphic, but in the subclass, it'll choose the default graphic. Is this a violation of the Liskov Substitution Principal? Does the fact that subclasses are almost intended to use different parameter lists have any bearing on this? Would minimizing the parameter list violate it in a case like this? Thanks.

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  • Very simple OOP question

    - by Mosty Mostacho
    I was creating and discussing a class diagram with a partner of mine. To simplify things, I've modify the real domain we're working on and made up the following diagram: Basically, a company works on constructions that are quite different one from each other but are still constructions. Note I've added one field for each class but there should be many more. Now, I thought this was the way to go but my partner told me that if in the future new construction classes appear we would have to modify the Company class, which is correct. So the new proposed class diagram would be this: Now I've been wondering: Should the fact that in no place of the application will there be mixed lists of planes and bridges affect the design in any way? When we have to list only planes for a company, how are we supposed to distinguish them from the other elements in the list without checking for their class names? Related to the previous question, is it correct to assume that this type of diagram should be high-level and this is something it shouldn't matter at this stage but rather be thought and decided at implementation time? Any comment will be appreciated.

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  • Class hierarchy problem in this social network model

    - by Gerenuk
    I'm trying to design a class system for a social network data model - basically a link/object system. Now I have roughly the following structure (simplified and only relevant methods shown) class Data: "used to handle the data with mongodb" "can link, unlink data and also return other linked data" "is basically a proxy object that only stores _id and accesses mongodb on requests" "it looks like {_id: ..., _out: [id1, id2,...], _inc: [id3, id4, ...]}" def get_node(self, id) "create a new Data object from the underlying mongodb" "each data object can potentially create a reference object to new mongo data" "this is needed when the data returns the linked objects" class Node: """ this class proxies linking calls to .data it includes additional network logic operations whereas Data only contains a basic database solution """ def __init__(self, data): "the infrastructure realization is stored as composition by an included object data" "Node bascially proxies most calls to the infrastructure object data" def get_node(self, data): "creates a new object of class Object or Link depending on data" class Object(Node): "can have multiple connections to Link" class Link(Node): "has one 'in' and one 'out' connection to an Object" This system is working, however maybe wouldn't work outside Python. Note that after reading links Now I have two questions here: 1) I want to infrastructure of the data storage to be replacable. Earlier I had Data as a superclass of Node so that it provided the neccessary calls. But (without dirty Python tricks) you cannot replace the superclass dynamically. Is using composition therefore recommended? The drawback is that I have to proxy most calls (link, unlink etc). Any thoughts? 2) The class Node contains the common method .get_node which is used to built new Object or Link instances after reading out the data. Some attribute of data decided whether the object which is only stored by id should be instantiated as an Object or Link class. The problem here is that Node needs to know about Object and Link in advance, which seems dodgy. Do you see a different solution? Both Object and Link need to instantiate one of all possible types depending on what the find in their linked data. Are there any other ideas how to implement a flexible Object/Link structure where the underlying database storage is isolated?

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  • Implementation of instance testing in Java, C++, C#

    - by Jake
    For curiosity purposes as well as understanding what they entail in a program, I'm curious as to how instance testing (instanceof/is/using dynamic_cast in c++) works. I've tried to google it (particularly for java) but the only pages that come up are tutorials on how to use the operator. How do the implementations vary across those langauges? How do they treat classes with identical signatures? Also, it's been drilled into my head that using instance testing is a mark of bad design. Why exactly is this? When is that applicable, instanceof should still be used in methods like .equals() and such right? I was also thinking of this in the context of exception handling, again particularly in Java. When you have mutliple catch statements, how does that work? Is that instance testing or is it just resolved during compilation where each thrown exception would go to?

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  • How do you handle objects that need custom behavior, and need to exist as an entity in the database?

    - by Scott Whitlock
    For a simple example, assume your application sends out notifications to users when various events happen. So in the database I might have the following tables: TABLE Event EventId uniqueidentifier EventName varchar TABLE User UserId uniqueidentifier Name varchar TABLE EventSubscription EventUserId EventId UserId The events themselves are generated by the program. So there are hard-coded points in the application where an event instance is generated, and it needs to notify all the subscribed users. So, the application itself doesn't edit the Event table, except during initial installation, and during an update where a new Event might be created. At some point, when an event is generated, the application needs to lookup the Event and get a list of Users. What's the best way to link the event in the source code to the event in the database? Option 1: Store the EventName in the program as a fixed constant, and look it up by name. Option 2: Store the EventId in the program as a static Guid, and look it up by ID. Extra Credit In other similar circumstances I may want to include custom behavior with the event type. That is, I'll want subclasses of my Event entity class with different behaviors, and when I lookup an event, I want it to return an instance of my subclass. For instance: class Event { public Guid Id { get; } public Guid EventName { get; } public ReadOnlyCollection<EventSubscription> EventSubscriptions { get; } public void NotifySubscribers() { foreach(var eventSubscription in EventSubscriptions) { eventSubscription.Notify(); } this.OnSubscribersNotified(); } public virtual void OnSubscribersNotified() {} } class WakingEvent : Event { private readonly IWaker waker; public WakingEvent(IWaker waker) { if(waker == null) throw new ArgumentNullException("waker"); this.waker = waker; } public override void OnSubscribersNotified() { this.waker.Wake(); base.OnSubscribersNotified(); } } So, that means I need to map WakingEvent to whatever key I'm using to look it up in the database. Let's say that's the EventId. Where do I store this relationship? Does it go in the event repository class? Should the WakingEvent know declare its own ID in a static member or method? ...and then, is this all backwards? If all events have a subclass, then instead of retrieving events by ID, should I be asking my repository for the WakingEvent like this: public T GetEvent<T>() where T : Event { ... // what goes here? ... } I can't be the first one to tackle this. What's the best practice?

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  • What alternative is better to diagram this scenario?

    - by Mosty Mostacho
    I was creating and discussing a class diagram with a partner of mine. To simplify things, I've modify the real domain we're working on and made up the following diagram: Basically, a company works on constructions that are quite different one from each other but are still constructions. Note I've added one field for each class but there should be many more. Now, I thought this was the way to go but my partner told me that if in the future new construction classes appear we would have to modify the Company class, which is correct. So the new proposed class diagram would be this: Now I've been wondering: Should the fact that in no place of the application will there be mixed lists of planes and bridges affect the design in any way? When we have to list only planes for a company, how are we supposed to distinguish them from the other elements in the list without checking for their class names? Related to the previous question, is it correct to assume that this type of diagram should be high-level and this is something it shouldn't matter at this stage but rather be thought and decided at implementation time? Any comment will be appreciated.

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  • Avoid overwriting all the methods in the child class

    - by Heckel
    The context I am making a game in C++ using SFML. I have a class that controls what is displayed on the screen (manager on the image below). It has a list of all the things to draw like images, text, etc. To be able to store them in one list I created a Drawable class from which all the other drawable class inherit. The image below represents how I would organize each class. Drawable has a virtual method Draw that will be called by the manager. Image and Text overwrite this method. My problem is that I would like Image::draw method to work for Circle, Polygon, etc. since sf::CircleShape and sf::ConvexShape inherit from sf::Shape. I thought of two ways to do that. My first idea would be for Image to have a pointer on sf::Shape, and the subclasses would make it point onto their sf::CircleShape or sf::ConvexShape classes (Like on the image below). In the Polygon constructor I would write something like ptr_shape = &polygon_shape; This doesn't look very elegant because I have two variables that are, in fact, just one. My second idea is to store the sf::CircleShape and sf::ConvexShape inside the ptr_shape like ptr_shape = new sf::ConvexShape(...); and to use a function that is only in ConvexShape I would cast it like so ((sf::ConvexShape*)ptr_shape)->convex_method(); But that doesn't look very elegant either. I am not even sure I am allowed to do that. My question I added details about the whole thing because I thought that maybe my whole architecture was wrong. I would like to know how I could design my program to be safe without overwriting all the Image methods. I apologize if this question has already been asked; I have no idea what to google.

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  • Are trivial protected getters blatant overkill?

    - by Panzercrisis
    Something I really have not thought about before (AS3 syntax): private var m_obj:Object; protected function get obj():Object { return m_obj; } private var m_str:String; protected function get str():String { return m_str; } At least subclasses won't be able to set m_obj or m_str (though they could still modify m_obj). Is this just blatant overkill? I am not talking about doing this as opposed to making them public. I am talking about doing this instead of just making the variables themselves protected. Like this: protected var m_obj:Object; //more accessible than a private variable with a protected getter protected var m_str:String; //more accessible than a private variable with a protected getter

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  • OO Software Architecture - base class that everything inherits from. Bad/good idea?

    - by ale
    I am reviewing a proposed OO software architecture that looks like this: Base Foo Something Bar SomethingElse Where Base is a static class. My immediate thought was that every object in any class will inherit all the methods in Base which would create a large object. Could this cause problems for a large system? The whole architecture is hierarchical.. the 'tree' is much bigger than this really. Does this sort of architecture have a name (hierarchical?!). What are the known pros and cons?

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  • REST API wrapper - class design for 'lite' object responses

    - by sasfrog
    I am writing a class library to serve as a managed .NET wrapper over a REST API. I'm very new to OOP, and this task is an ideal opportunity for me to learn some OOP concepts in a real-life situation that makes sense to me. Some of the key resources/objects that the API returns are returned with different levels of detail depending on whether the request is for a single instance, a list, or part of a "search all resources" response. This is obviously a good design for the REST API itself, so that full objects aren't returned (thus increasing the size of the response and therefore the time taken to respond) unless they're needed. So, to be clear: .../car/1234.json returns the full Car object for 1234, all its properties like colour, make, model, year, engine_size, etc. Let's call this full. .../cars.json returns a list of Car objects, but only with a subset of the properties returned by .../car/1234.json. Let's call this lite. ...search.json returns, among other things, a list of car objects, but with minimal properties (only ID, make and model). Let's call this lite-lite. I want to know what the pros and cons of each of the following possible designs are, and whether there is a better design that I haven't covered: Create a Car class that models the lite-lite properties, and then have each of the more detailed responses inherit and extend this class. Create separate CarFull, CarLite and CarLiteLite classes corresponding to each of the responses. Create a single Car class that contains (nullable?) properties for the full response, and create constructors for each of the responses which populate it to the extent possible (and maybe include a property that returns the response type from which the instance was created). I expect among other things there will be use cases for consumers of the wrapper where they will want to iterate through lists of Cars, regardless of which response type they were created from, such that the three response types can contribute to the same list. Happy to be pointed to good resources on this sort of thing, and/or even told the name of the concept I'm describing so I can better target my research.

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  • Is "If a method is re-used without changes, put the method in a base class, else create an interface" a good rule-of-thumb?

    - by exizt
    A colleague of mine came up with a rule-of-thumb for choosing between creating a base class or an interface. He says: Imagine every new method that you are about to implement. For each of them, consider this: will this method be implemented by more than one class in exactly this form, without any change? If the answer is "yes", create a base class. In every other situation, create an interface. For example: Consider the classes cat and dog, which extend the class mammal and have a single method pet(). We then add the class alligator, which doesn't extend anything and has a single method slither(). Now, we want to add an eat() method to all of them. If the implementation of eat() method will be exactly the same for cat, dog and alligator, we should create a base class (let's say, animal), which implements this method. However, if it's implementation in alligator differs in the slightest way, we should create an IEat interface and make mammal and alligator implement it. He insists that this method covers all cases, but it seems like over-simplification to me. Is it worth following this rule-of-thumb?

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  • Puppet class inheritance confusion

    - by EMiller
    I've read the documentation on scope, but I'm still having trouble working this out. I've got two environments that are very similar - so I've got: modules/django-env/manifests/init.pp class django-env { package { "python26": ensure => installed } # etc ... } import "er.pp" modules/django-env/manifests/er.pp $venvname = "er" $venvpath = "/home/django/virtualenvs" class er { file { "$venvpath/$venvname" : ensure => directory } # etc ... } class er-dev { include er } class er-bce-dev { $venvname = "er-bce" include er } manifests/modules.pp import "django-env" manifests/nodes.pp node default { # etc ... } node 'centos-dev' imports default { include django-env include er-bce-dev include er-dev } The result here is that the "inheritance" works - but only the first "er-" item under the 'centos-dev' node is acted upon, I either get er-bce-dev or er-dev, but not both. There must be some basic thing I'm misunderstanding here. Is it the difference between import and include ? (not sure I understand that)

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  • converting node inheritance to hiera

    - by quickshiftin
    I'm working on moving over a node inheritance tree to hiera. Presently working on the hierarchy. Prior to hiera, my nodes had a hierarchy as such base pre-prod qa nodes staging nodes development nodes prod nodes Now I'm trying to get the same tier with hiera. Starting out I have this :hierarchy: - base - "%{environment}" - "%{clientcert}" but I need another level to capture pre-prod and prod. My thought would be to add an entry to puppet.conf, something like [agent] realm = pre-prod then :hierarchy: - base - "%{realm}" - "%{environment}" - "%{clientcert}" A couple of questions Are you allowed to place arbitrary properties into puppet.conf? Will hiera see the realm property?

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  • Boost.Python wrapping hierarchies avoiding diamond inheritance

    - by stbuton
    I'm having some trouble seeing what the best way to wrap a series of classes with Boost.Python while avoiding messy inheritance problems. Say I have the classes A, B, and C with the following structure: struct A { virtual void foo(); virtual void bar(); virtual void baz(); }; struct B : public A { virtual void quux(); }; struct C : public A { virtual void foobar(); }; I want to wrap all classes A, B, and C such that they are extendable from Python. The normal method for accomplishing this would be along the lines of: struct A_Wrapper : public A, boost::python::wrapper<A> { //dispatch logic for virtual functions }; Now for classes B and C which extend from A I would like to be able to inherit and share the wrapping implementation for A. So I'd like to be able to do something along the lines of: struct B_Wrapper : public B, public A_Wrapper, public boost::python::wrapper<B> { //dispatch logic specific for B }; struct C_Wrapper : public C, public A_Wrapper, public boost::python::wrapper<C> { //dispatch logic specific for C } However, it seems like that would introduce all manner of nastiness with the double inheritance of the boost wrapper base and the double inheritance of A in the B_Wrapper and C_Wrapper objects. Is there a common way that this instance is solved that I'm missing? thanks.

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  • Inheritance concept in jpa

    - by megala
    I created one table using Inheritance concept to sore data into google app engine datastore. It contained following coding but it shows error.How to user Inheritance concept.What error in my program Program 1: @Entity @Inheritance(strategy=InheritanceType.JOINED) public class calender { @Id private String EmailId; @Basic private String CalName; @Basic public void setEmailId(String emailId) { EmailId = emailId; } public String getEmailId() { return EmailId; } public void setCalName(String calName) { CalName = calName; } public String getCalName() { return CalName; } public calender(String EmailId,String CalName) { this.EmailId=EmailId; this.CalName=CalName; } } program 2: @Entity public class method { @Id private String method; public void setMethod(String method) { this.method = method; } public String getMethod() { return method; } public method(String method) { this.method=method; } } My constraint is I want ouput like this Calendertable coantain Emailid calenername and method table contain Emailid method How to achive this? thanks inadvance.

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  • C++ code visualization

    - by bobobobo
    A sort of follow up/related question to this. I'm trying to get a grip on a large code base that has hundreds and hundreds of classes and a large inheritance hierarchy. I want to be able to see the "main veins" of the inheritance hierarchy at a glance - not all the "peripheral" classes that only do some very specific / specialized thing. Visual Studio's "View Class Diagram" makes something that looks like a train and its sprawled horizontally across the screen and isn't very organized. You can't grok it easily. I've just tried doxygen and graphviz but the results are .. somewhat similar to Visual Studio. I'm getting sweet looking call graphs but again too much detail for what I'm trying to get. I need a quick way to generate the inheritance hierarchy, in some kind of collapsible view.

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  • Log4r : logger inheritance, yaml configuration, alternatives ?

    - by devlearn
    Hello, I'm pretty new to ruby environments and I was looking for a nice logging framework to use it my ruby and rails applications. In my previous experiences I have successfully used log4j and log4p (the perl port) and was expecting the same level of usability (and maturity) with log4r. However I must say that there are a number of things that are not clear at all in the log4r framework. 1 Logger Inheritance The logger inheritance does not seem to be managed at all ! If I declare a logger named 'myapp' and then try to get a logger name 'myapp::engine', the lookup will end with a NameError. I would expect that the framework returns the root logger according to the naming scheme and to use the 'myapp' logger. Q1 : Of course I can work around this and manage the names by myself with a lookup method, however is there a cleaner way to do this without any extra coding ? 2 YAML configuration Second thing that confuses me is the yaml configuration. On the log4r site there are literally no information about this system, the doc links forward to missing pages, so all the info I can find about is contained in the examples directory of the gem. I was pretty confused with the fact that the yaml configuration must contain the pre_config section, and that I need to define my own levels. If I remove the pre_config secion, or replace all the “custom” levels by the standard ones ( debug, info, warn, fatal ) , the example will throw the following error : log4r/yamlconfigurator.rb:68:in `decode_yaml': Log level must be in 0..7 (ArgumentError) So there seems to be no way of using a simple file where we only declare the loggers and appenders for the framework. Q2 : I realy think that I missed something and that must be a way of providing a simple yaml conf file. Do you have any examples of such an usage ? 3 Variables substitution in XML file Q3 : The Yaml configuration system seems to provide such a feature however I was unable to find a similar feature with XML files. Any ideas ? 4 Alternatives ? I must say that I'm very disappointed by the feature level and the maturity of log4r compared to the log4j and other log4j ports. I run into this framework with a solid background of logging APIs in other languages and find myself working around in all kinds just to make 'basic things' running in a “real world application”. By that I mean a complex application composed of several gems, console/scripting apps, and a rails web front end where the configuration must be mutualized and where we make intensive usage of namespaces and inheritance. I've run several searches in order to find something more suitable or mature, but did not find anything similar. Q4 : Do you guys know any (serious) alternatives to log4r framework that could be used in a enterprise class app ? Thanks reading all of this ! I'd really appreciate any pointers, Kind Regards,

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  • How to perform insert and update with Ado.net dataservices (EF and Inheritance)

    - by Thurein
    Hi, I have an entity model, in which I have a table per type inheritance. There are 3 types, first, Contact, which I defined as abstract in my EF model and the rest are Company and person types which are derived from contact type. Is it possible to perform an insert using ado.net dataservice and asp.net ajax library? I was trying the following client code : dataContext.insertEntity(person, "Contacts"); I was getting this response from server : Error processing request stream. Type information must be specified for types that take part in inheritance. Thanks.

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  • Fixtures and inheritance in Symfony

    - by Tere
    Hi! I have a database schema in Symfony like this: Persona: actAs: { Timestampable: ~ } columns: primer_nombre: { type: string(255), notnull: true } segundo_nombre: { type: string(255) } apellido: { type: string(255), notnull: true } rut: { type: string(255) } email: { type: string(255) } email2: { type: string(255) } direccion: { type: string(400) } ciudad: { type: string(255) } region: { type: string(255) } pais: { type: string(255) } telefono: { type: string(255) } telefono2: { type: string(255) } fecha_nacimiento: { type: date } Alumno: inheritance: type: concrete extends: Persona columns: comentario: { type: string(255) } estado_pago: { type: string(255) } Alumno_Beca: columns: persona_id: { type: integer, primary: true } beca_id: { type: integer, primary: true } relations: Alumno: { onDelete: CASCADE, local: persona_id, foreign: id } Beca: { onDelete: CASCADE, local: beca_id, foreign: id } Beca: columns: nombre: { type: string(255) } monto: { type: double } porcentaje: { type: double } descripcion: { type: string(5000) } As you see, "alumno" has a concrete inheritance from "persona". Now I'm trying to create fixtures for this two tables, and I can't make Doctrine to load them. It gives me this error: SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (eat/alumno__beca, CONSTRAINT alumno__beca_persona_id_alumno_id FOREIGN KEY (persona_id) REFERENCES alumno (id) ON DELETE CASCADE) Does someone know how to write a fixture for a table inherited from another? Thanks!

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