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• Persistent (purely functional) Red-Black trees on disk performance

  - by Waneck

  I'm studying the best data structures to implement a simple open-source object temporal database, and currently I'm very fond of using Persistent Red-Black trees to do it. My main reasons for using persistent data structures is first of all to minimize the use of locks, so the database can be as parallel as possible. Also it will be easier to implement ACID transactions and even being able to abstract the database to work in parallel on a cluster of some kind. The great thing of this approach is that it makes possible implementing temporal databases almost for free. And this is something quite nice to have, specially for web and for data analysis (e.g. trends). All of this is very cool, but I'm a little suspicious about the overall performance of using a persistent data structure on disk. Even though there are some very fast disks available today, and all writes can be done asynchronously, so a response is always immediate, I don't want to build all application under a false premise, only to realize it isn't really a good way to do it. Here's my line of thought: - Since all writes are done asynchronously, and using a persistent data structure will enable not to invalidate the previous - and currently valid - structure, the write time isn't really a bottleneck. - There are some literature on structures like this that are exactly for disk usage. But it seems to me that these techniques will add more read overhead to achieve faster writes. But I think that exactly the opposite is preferable. Also many of these techniques really do end up with a multi-versioned trees, but they aren't strictly immutable, which is something very crucial to justify the persistent overhead. - I know there still will have to be some kind of locking when appending values to the database, and I also know there should be a good garbage collecting logic if not all versions are to be maintained (otherwise the file size will surely rise dramatically). Also a delta compression system could be thought about. - Of all search trees structures, I really think Red-Blacks are the most close to what I need, since they offer the least number of rotations. But there are some possible pitfalls along the way: - Asynchronous writes -could- affect applications that need the data in real time. But I don't think that is the case with web applications, most of the time. Also when real-time data is needed, another solutions could be devised, like a check-in/check-out system of specific data that will need to be worked on a more real-time manner. - Also they could lead to some commit conflicts, though I fail to think of a good example of when it could happen. Also commit conflicts can occur in normal RDBMS, if two threads are working with the same data, right? - The overhead of having an immutable interface like this will grow exponentially and everything is doomed to fail soon, so this all is a bad idea. Any thoughts? Thanks! edit: There seems to be a misunderstanding of what a persistent data structure is: http://en.wikipedia.org/wiki/Persistent_data_structure

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• Multi-tier applications using L2S, WCF and Base Class

  - by Gena Verdel

  Hi all. One day I decided to build this nice multi-tier application using L2S and WCF. The simplified model is : DataBase-L2S-Wrapper(DTO)-Client Application. The communication between Client and Database is achieved by using Data Transfer Objects which contain entity objects as their properties. abstract public class BaseObject { public virtual IccSystem.iccObjectTypes ObjectICC_Type { get { return IccSystem.iccObjectTypes.unknownType; } } [global::System.Data.Linq.Mapping.ColumnAttribute(Storage = "_ID", AutoSync = AutoSync.OnInsert, DbType = "BigInt NOT NULL IDENTITY", IsPrimaryKey = true, IsDbGenerated = true)] [global::System.Runtime.Serialization.DataMemberAttribute(Order = 1)] public virtual long ID { //get; //set; get { return _ID; } set { _ID = value; } } } [DataContract] public class BaseObjectWrapper<T> where T : BaseObject { #region Fields private T _DBObject; #endregion #region Properties [DataMember] public T Entity { get { return _DBObject; } set { _DBObject = value; } } #endregion } Pretty simple, isn't it?. Here's the catch. Each one of the mapped classes contains ID property itself so I decided to override it like this [global::System.Data.Linq.Mapping.TableAttribute(Name="dbo.Divisions")] [global::System.Runtime.Serialization.DataContractAttribute()] public partial class Division : INotifyPropertyChanging, INotifyPropertyChanged { [global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_ID", AutoSync=AutoSync.OnInsert, DbType="BigInt NOT NULL IDENTITY", IsPrimaryKey=true, IsDbGenerated=true)] [global::System.Runtime.Serialization.DataMemberAttribute(Order=1)] public override long ID { get { return this._ID; } set { if ((this._ID != value)) { this.OnIDChanging(value); this.SendPropertyChanging(); this._ID = value; this.SendPropertyChanged("ID"); this.OnIDChanged(); } } } } Wrapper for division is pretty straightforward as well: public class DivisionWrapper : BaseObjectWrapper<Division> { } It worked pretty well as long as I kept ID values at mapped class and its BaseObject class the same(that's not very good approach, I know, but still) but then this happened: private CentralDC _dc; public bool UpdateDivision(ref DivisionWrapper division) { DivisionWrapper tempWrapper = division; if (division.Entity == null) { return false; } try { Table<Division> table = _dc.Divisions; var q = table.Where(o => o.ID == tempWrapper.Entity.ID); if (q.Count() == 0) { division.Entity._errorMessage = "Unable to locate entity with id " + division.Entity.ID.ToString(); return false; } var realEntity = q.First(); realEntity = division.Entity; _dc.SubmitChanges(); return true; } catch (Exception ex) { division.Entity._errorMessage = ex.Message; return false; } } When trying to enumerate over the in-memory query the following exception occurred: Class member BaseObject.ID is unmapped. Although I'm stating the type and overriding the ID property L2S fails to work. Any suggestions?

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• Can't destroy record in many-to-many relationship

  - by Dmart

  I'm new to Rails, so I'm sure I've made a simple mistake. I've set up a many-to-many relationship between two models: User and Group. They're connected through the junction model GroupMember. Here are my models (removed irrelevant stuff): class User < ActiveRecord::Base has_many :group_members has_many :groups, :through => :group_members end class GroupMember < ActiveRecord::Base belongs_to :group belongs_to :user end class Group < ActiveRecord::Base has_many :group_members has_many :users, :through => :group_members end The table for GroupMembers contains additional information about the relationship, so I didn't use has_and_belongs_to_many (as per the Rails "Active Record Associations" guide). The problem I'm having is that I can't destroy a GroupMember. Here's the output from rails console: irb(main):006:0> m = GroupMember.new => #<GroupMember group_id: nil, user_id: nil, active: nil, created_at: nil, updated_at: nil> irb(main):007:0> m.group_id =1 => 1 irb(main):008:0> m.user_id = 16 => 16 irb(main):009:0> m.save => true irb(main):010:0> m.destroy NoMethodError: undefined method `eq' for nil:NilClass from /usr/local/lib/ruby/gems/1.8/gems/activesupport-3.0.4/lib/active_support/whiny_nil.rb:48:in `method_missing' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/persistence.rb:79:in `destroy' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/locking/optimistic.rb:110:in `destroy' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/callbacks.rb:260:in `destroy' from /usr/local/lib/ruby/gems/1.8/gems/activesupport-3.0.4/lib/active_support/callbacks.rb:413:in `_run_destroy_callbacks' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/callbacks.rb:260:in `destroy' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:235:in `destroy' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:292:in `with_transaction_returning_status' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/connection_adapters/abstract/database_statements.rb:139:in `transaction' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:207:in `transaction' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:290:in `with_transaction_returning_status' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:235:in `destroy' from (irb):10 This is driving me crazy, so any help would be greatly appreciated.

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• Help with method logic in Java, hw

  - by Crystal

  I have a Loan class that in its printPayment method, it prints the amortization table of a loan for a hw assignment. We are also to implement a print first payment method, and a print last payment method. Since my calculation is done in the printPayment method, I didn't know how I could get the value in the first or last iteration of the loop and print that amount out. One way I can think of is to write a new method that might return that value, but I wasn't sure if there was a better way. Here is my code: public abstract class Loan { public void setClient(Person client) { this.client = client; } public Person getClient() { return client; } public void setLoanId() { loanId = nextId; nextId++; } public int getLoanId() { return loanId; } public void setInterestRate(double interestRate) { this.interestRate = interestRate; } public double getInterestRate() { return interestRate; } public void setLoanLength(int loanLength) { this.loanLength = loanLength; } public int getLoanLength() { return loanLength; } public void setLoanAmount(double loanAmount) { this.loanAmount = loanAmount; } public double getLoanAmount() { return loanAmount; } public void printPayments() { double monthlyInterest; double monthlyPrincipalPaid; double newPrincipal; int paymentNumber = 1; double monthlyInterestRate = interestRate / 1200; double monthlyPayment = loanAmount * (monthlyInterestRate) / (1 - Math.pow((1 + monthlyInterestRate),( -1 * loanLength))); System.out.println("Payment Number | Interest | Principal | Loan Balance"); // amortization table while (loanAmount >= 0) { monthlyInterest = loanAmount * monthlyInterestRate; monthlyPrincipalPaid = monthlyPayment - monthlyInterest; newPrincipal = loanAmount - monthlyPrincipalPaid; loanAmount = newPrincipal; System.out.printf("%d, %.2f, %.2f, %.2f", paymentNumber++, monthlyInterest, monthlyPrincipalPaid, loanAmount); } } /* //method to print first payment public double getFirstPayment() { } method to print last payment public double getLastPayment() { }*/ private Person client; private int loanId; private double interestRate; private int loanLength; private double loanAmount; private static int nextId = 1; } Thanks!

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• c++ class member functions instatiated by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched stackoverflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state info was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (vc++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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• Any way to allow classes implementing IEntity and downcast to have operator == comparisons?

  - by George Mauer

  Basically here's the issue. All entities in my system are identified by their type and their id. new Customer() { Id = 1} == new Customer() {Id = 1}; new Customer() { Id = 1} != new Customer() {Id = 2}; new Customer() { Id = 1} != new Product() {Id = 1}; Pretty standard scenario. Since all Entities have an Id I define an interface for all entities. public interface IEntity { int Id { get; set;} } And to simplify creation of entities I make public abstract class BaseEntity<T> : where T : IEntity { int Id { get; set;} public static bool operator ==(BaseEntity<T> e1, BaseEntity<T> e2) { if (object.ReferenceEquals(null, e1)) return false; return e1.Equals(e2); } public static bool operator !=(BaseEntity<T> e1, BaseEntity<T> e2) { return !(e1 == e2); } } where Customer and Product are something like public class Customer : BaseEntity<Customer>, IEntity {} public class Product : BaseEntity<Product>, IEntity {} I think this is hunky dory. I think all I have to do is override Equals in each entity (if I'm super clever, I can even override it only once in the BaseEntity) and everything with work. So now I'm expanding my test coverage and find that its not quite so simple! First of all , when downcasting to IEntity and using == the BaseEntity< override is not used. So what's the solution? Is there something else I can do? If not, this is seriously annoying. Upadate It would seem that there is something wrong with my tests - or rather with comparing on generics. Check this out [Test] public void when_created_manually_non_generic() { // PASSES! var e1 = new Terminal() {Id = 1}; var e2 = new Terminal() {Id = 1}; Assert.IsTrue(e1 == e2); } [Test] public void when_created_manually_generic() { // FAILS! GenericCompare(new Terminal() { Id = 1 }, new Terminal() { Id = 1 }); } private void GenericCompare<T>(T e1, T e2) where T : class, IEntity { Assert.IsTrue(e1 == e2); } Whats going on here? This is not as big a problem as I was afraid, but is still quite annoying and a completely unintuitive way for the language to behave. Update Update Ah I get it, the generic implicitly downcasts to IEntity for some reason. I stand by this being unintuitive and potentially problematic for my Domain's consumers as they need to remember that anything happening within a generic method or class needs to be compared with Equals()

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• Representing xml through a single class

  - by Charles

  I am trying to abstract away the difficulties of configuring an application that we use. This application takes a xml configuration file and it can be a bit bothersome to manually edit this file, especially when we are trying to setup some automatic testing scenarios. I am finding that reading xml is nice, pretty easy, you get a network of element nodes that you can just go through and build your structures quite nicely. However I am slowly finding that the reverse is not quite so nice. I want to be able to build a xml configuration file through a single easy to use interface and because xml is composed of a system of nodes I am having a lot of struggle trying to maintain the 'easy' part. Does anyone know of any examples or samples that easily and intuitively build xml files without declaring a bunch of element type classes and expect the user to build the network themselves? For example if my desired xml output is like so <cook version="1.1"> <recipe name="chocolate chip cookie"> <ingredients> <ingredient name="flour" amount="2" units="cups"/> <ingredient name="eggs" amount="2" units="" /> <ingredient name="cooking chocolate" amount="5" units="cups" /> </ingredients> <directions> <direction name="step 1">Preheat oven</direction> <direction name="step 2">Mix flour, egg, and chocolate</direction> <direction name="step 2">bake</direction> </directions> </recipe> <recipe name="hot dog"> ... How would I go about designing a class to build that network of elements and make one easy to use interface for creating recipes? Right now I have a recipe object, an ingredient object, and a direction object. The user must make each one, set the attributes in the class and attach them to the root object which assembles the xml elements and outputs the formatted xml. Its not very pretty and I just know there has to be a better way. I am using python so bonus points for pythonic solutions

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• Is it Bad Practice to use C++ only for the STL containers?

  - by gmatt

  First a little background ... In what follows, I use C,C++ and Java for coding (general) algorithms, not gui's and fancy program's with interfaces, but simple command line algorithms and libraries. I started out learning about programming in Java. I got pretty good with Java and I learned to use the Java containers a lot as they tend to reduce complexity of book keeping while guaranteeing great performance. I intermittently used C++, but I was definitely not as good with it as with Java and it felt cumbersome. I did not know C++ enough to work in it without having to look up every single function and so I quickly reverted back to sticking to Java as much as possible. I then made a sudden transition into cracking and hacking in assembly language, because I felt I was concentrated too much attention on a much too high level language and I needed more experience with how a CPU interacts with memory and whats really going on with the 1's and 0's. I have to admit this was one of the most educational and fun experiences I've had with computers to date. For obviously reasons, I could not use assembly language to code on a daily basis, it was mostly reserved for fun diversions. After learning more about the computer through this experience I then realized that C++ is so much closer to the "level of 1's and 0's" than Java was, but I still felt it to be incredibly obtuse, like a swiss army knife with far too many gizmos to do any one task with elegance. I decided to give plain vanilla C a try, and I quickly fell in love. It was a happy medium between simplicity and enough "micromanagent" to not abstract what is really going on. However, I did miss one thing about Java: the containers. In particular, a simple container (like the stl vector) that expands dynamically in size is incredibly useful, but quite a pain to have to implement in C every time. Hence my code currently looks like almost entirely C with containers from C++ thrown in, the only feature I use from C++. I'd like to know if its consider okay in practice to use just one feature of C++, and ignore the rest in favor of C type code?

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• Is there a reason why a base class decorated with XmlInclude would still throw a type unknown exception when serialized?

  - by Tedford

  I will simplify the code to save space but what is presented does illustrate the core problem. I have a class which has a property that is a base type. There exist 3 dervived classes which could be assigned to that property. If I assign any of the derived classes to the container then the XmlSerializer throws dreaded "The type xxx was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically." exception when attempting to seralize the container. However my base class is already decorated with that attribute so I figure there must be an additional "hidden" requirement. The really odd part is that the default WCF serializer has no issues with this class hierarchy. The Container class [DataContract] [XmlRoot(ElementName = "TRANSACTION", Namespace = Constants.Namespace)] public class PaymentSummaryRequest : CommandRequest { /// <summary> /// Gets or sets the summary. /// </summary> /// <value>The summary.</value> /// <remarks></remarks> [DataMember] public PaymentSummary Summary { get; set; } /// <summary> /// Initializes a new instance of the <see cref="PaymentSummaryRequest"/> class. /// </summary> public PaymentSummaryRequest() { Mechanism = CommandMechanism.PaymentSummary; } } The base class [DataContract] [XmlInclude(typeof(xxxPaymentSummary))] [XmlInclude(typeof(yyyPaymentSummary))] [XmlInclude(typeof(zzzPaymentSummary))] [KnownType(typeof(xxxPaymentSummary))] [KnownType(typeof(xxxPaymentSummary))] [KnownType(typeof(zzzPaymentSummary))] public abstract class PaymentSummary { } One of the derived classes [DataContract] public class xxxPaymentSummary : PaymentSummary { } The serialization code var serializer = new XmlSerializer(typeof(PaymentSummaryRequest)); serializer.Serialize(Console.Out,new PaymentSummaryRequest{Summary = new xxxPaymentSummary{}}); The Exception System.InvalidOperationException: There was an error generating the XML document. --- System.InvalidOperationException: The type xxxPaymentSummary was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically. at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterPaymentSummaryRequest.Write13_PaymentSummary(String n, String ns, PaymentSummary o, Boolean isNullable, Boolean needType) at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterPaymentSummaryRequest.Write14_PaymentSummaryRequest(String n, String ns, PaymentSummaryRequest o, Boolean isNullable, Boolean needType) at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterPaymentSummaryRequest.Write15_TRANSACTION(Object o) --- End of inner exception stack trace --- at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id) at System.Xml.Serialization.XmlSerializer.Serialize(TextWriter textWriter, Object o, XmlSerializerNamespaces namespaces) at UserQuery.RunUserAuthoredQuery() in c:\Users\Tedford\AppData\Local\Temp\uqacncyo.0.cs:line 47

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• Java loading user-specified classes at runtime

  - by user349043

  I'm working on robot simulation in Java (a Swing application). I have an abstract class "Robot" from which different types of Robots are derived, e.g. public class StupidRobot extends Robot { int m_stupidness; int m_insanityLevel; ... } public class AngryRobot extends Robot { float m_aggression; ... } As you can see, each Robot subclass has a different set of parameters. What I would like to do is control the simulation setup in the initial UI. Choose the number and type of Robots, give it a name, fill in the parameters etc. This is one of those times where being such a dinosaur programmer, and new to Java, I wonder if there is some higher level stuff/thinking that could help me here. So here is what I've got: (1) User Interface Scrolling list of Robot types on the left. "Add " and "<< Remove" buttons in the middle. Default-named scrolling list of Robots on the right. "Set Parameters" button underneath. (So if you wanted an AngryRobot, you'd select AngryRobot on the left list, click "Add" and "AngryRobot1" would show up on the right.) When selecting a Robot on the right, click "Set Parameters..." button which would call yet another model dialog where you'd fill in the parameters. Different dialog called for each Robot type. (2) Data structures an implementation As an end-product I think a HashMap would be most convenient. The keys would be Robot types and the accompanying object would be all of the parameters. The initializer could just retrieve each item one and a time and instantiate. Here's what the data structures would look like: enum ROBOT_TYPE {STUPID, ANGRY, etc} public class RobotInitializer { public ROBOT_TYPE m_type; public string m_name; public int[] m_int_params; public float[] m_float_params; etc. The initializer's constructor would create the appropriate length parameter arrays based on the type: public RobotInitializer(ROBOT_TYPE type, int[] int_array, float[] float_array, etc){ switch (type){ case STUPID: m_int_params = new int[STUPID_INT_PARAM_LENGTH]; System.arraycopy(int_array,0,m_int_params,0,STUPID_INT_PARAM_LENGTH); etc. Once all the RobotInitializers are instantiated, they are added to the HashMap. Iterating through the HashMap, the simulation initializer takes items from the Hashmap and instantiates the appropriate Robots. Is this reasonable? If not, how can it be improved? Thanks

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• MetadataType and client validation in ASP.NET MVC 2

  - by Kristoffer Ahl

  Inherited properties and MetadataType does not seem to work with client side validation in ASP.NET MVC 2. The validation of our MetadataTypes work as expected on the server but for some reason it does not generate the appropriate client scripts for it. Client side validation kicks in as expected for properties with the DataAnnotations attributes set on the PersonView so I know that client side validation is active and that it works. Does anyone know if or how it can be fixed? Here's what we have: public abstract class PersonView { public string FirstName { get; set; } public string LastName { get; set; } public string Email { get; set; } [Required] public string PhoneNumber { get; set; } public string AddressLine1 { get; set; } public string AddressLine2 { get; set; } public string AddressZipCode { get; set; } public string AddressCity { get; set; } public string AddressCountry { get; set; } } [MetadataType(typeof(CustomerViewMetaData))] public class CustomerView : PersonView {} [MetadataType(typeof(GuestViewMetaData))] public class GuestView : PersonView {} public class GuestViewMetaData { [Required(ErrorMessage = "The guests firstname is required")] public string FirstName { get; set; } [Required(ErrorMessage = "The guests lastname is required")] public string LastName { get; set; } } public class CustomerViewMetaData { [Required(ErrorMessage = "The customers firstname is required")] public string FirstName { get; set; } [Required(ErrorMessage = "The customers lastname is required")] public string LastName { get; set; } [Required(ErrorMessage = "The customers emails is required")] public string Email { get; set; } } As you can see, it's nothing fancy or strange in there... Can it be fixed? Is it a bug in ASP.NET MVC 2?

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• angular-ui-router : breadcrumps ok but view ko

  - by anakin59490

  this is my app.router.js : agentRouter.config([ '$stateProvider', '$urlRouterProvider', function($stateProvider, $urlRouterProvider) { var root = { name: 'root', abstract: true, url: '', title: 'home', views: { 'header': { templateUrl: 'views/headers/header.app.html', controller: 'HeaderCtrl' }, 'body': { templateUrl: "views/root.html" }, 'footer': { templateUrl: 'views/footers/footer.app.html' } } }; var agent = { name: 'root.agent', url: '/agent', title: 'agent', views: { 'root.sidebar': { templateUrl: "views/main.sidebar.html" }, 'root.container': { templateUrl: "views/partials/agent/list.container.html" } } }; var detail = { name: 'root.agent.detail', url: '/detail/:id', title: 'agentDetail', // use for breadcrumb views: { 'root.sidebar': { templateUrl: "views/main.sidebar.html" }, 'root.container': { templateUrl: "views/partials/agent/list.chantier.html" } } }; /.../ $stateProvider.state(root); $stateProvider.state(agent); $stateProvider.state(detail); } ]); and this is my root.html : <!--Breadcrumb content--> <ul class="row breadcrumb"> <i class="glyphicon glyphicon-home" style=""></i> <li ng-repeat="state in $state.$current.path"> <a ng-href="#{{state.url.format($stateParams)}}"><span ng-bind="state.title"></span></a> <span ng-hide="$last" class=""></span> </li> </ul> <!--Sidebar content--> <div ui-view="root.sidebar">default root.sidebar</div> <!--Container content--> <div style="background-color: #f9f9f9" ui-view="root.container">default root.container</div> I can access to my "agent" page (a list of person) and my breadcrumb is right : home / agent but when i click on an item of the list i got always the same page but my breadcrumb is right : home / agent / agentDetail but in app.router.js if change detail like this : var detail = { name: 'root.detail', // référence initiale + detail (fils) url: '/agent/detail/:id', // réference utilisée dans les fichiers HTML, attention c'est la suite de l'url précédente!!! title: 'agentDetail', // référence utilisée pour le breadcump views: { 'root.sidebar': { templateUrl: "views/main.sidebar.html" }, 'root.container': { templateUrl: "views/partials/agent/list.chantier.html" } } }; i got the right page (list.chantier.xml) but the breadcrumb is false : home / agentDetail instead of home / agent / agentDetail I would like to got the right breadcrumb (home / agent / agentDetail) with the right page (list.chantier.html) when i click on an item of the agent list page (list.container.html) Thank you in advance for your help

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• Which is the "best" data access framework/approach for C# and .NET?

  - by Frans

  (EDIT: I made it a community wiki as it is more suited to a collaborative format.) There are a plethora of ways to access SQL Server and other databases from .NET. All have their pros and cons and it will never be a simple question of which is "best" - the answer will always be "it depends". However, I am looking for a comparison at a high level of the different approaches and frameworks in the context of different levels of systems. For example, I would imagine that for a quick-and-dirty Web 2.0 application the answer would be very different from an in-house Enterprise-level CRUD application. I am aware that there are numerous questions on Stack Overflow dealing with subsets of this question, but I think it would be useful to try to build a summary comparison. I will endeavour to update the question with corrections and clarifications as we go. So far, this is my understanding at a high level - but I am sure it is wrong... I am primarily focusing on the Microsoft approaches to keep this focused. ADO.NET Entity Framework Database agnostic Good because it allows swapping backends in and out Bad because it can hit performance and database vendors are not too happy about it Seems to be MS's preferred route for the future Complicated to learn (though, see 267357) It is accessed through LINQ to Entities so provides ORM, thus allowing abstraction in your code LINQ to SQL Uncertain future (see Is LINQ to SQL truly dead?) Easy to learn (?) Only works with MS SQL Server See also Pros and cons of LINQ "Standard" ADO.NET No ORM No abstraction so you are back to "roll your own" and play with dynamically generated SQL Direct access, allows potentially better performance This ties in to the age-old debate of whether to focus on objects or relational data, to which the answer of course is "it depends on where the bulk of the work is" and since that is an unanswerable question hopefully we don't have to go in to that too much. IMHO, if your application is primarily manipulating large amounts of data, it does not make sense to abstract it too much into objects in the front-end code, you are better off using stored procedures and dynamic SQL to do as much of the work as possible on the back-end. Whereas, if you primarily have user interaction which causes database interaction at the level of tens or hundreds of rows then ORM makes complete sense. So, I guess my argument for good old-fashioned ADO.NET would be in the case where you manipulate and modify large datasets, in which case you will benefit from the direct access to the backend. Another case, of course, is where you have to access a legacy database that is already guarded by stored procedures. ASP.NET Data Source Controls Are these something altogether different or just a layer over standard ADO.NET? - Would you really use these if you had a DAL or if you implemented LINQ or Entities? NHibernate Seems to be a very powerful and powerful ORM? Open source Some other relevant links; NHibernate or LINQ to SQL Entity Framework vs LINQ to SQL

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• Robust way to save/load objects with dependencies?

  - by mrteacup

  I'm writing an Android game in Java and I need a robust way to save and load application state quickly. The question seems to apply to most OO languages. To understand what I need to save: I'm using a Strategy pattern to control my game entities. The idea is I have a very general Entity class which e.g. stores the location of a bullet/player/enemy and I then attach a Behaviour class that tells the entity how to act: class Entiy { float x; float y; Behavior b; } abstract class Behavior { void update(Entity e); {} // Move about at a constant speed class MoveBehavior extends Behavior { float speed; void update ... } // Chase after another entity class ChaseBehavior extends Behavior { Entity target; void update ... } // Perform two behaviours in sequence class CombineBehavior extends Behavior { Behaviour a, b; void update ... } Essentially, Entity objects are easy to save but Behaviour objects can have a semi-complex graph of dependencies between other Entity objects and other Behaviour objects. I also have cases where a Behaviour object is shared between entities. I'm willing to change my design to make saving/loading state easier, but the above design works really well for structuring the game. Anyway, the options I've considered are: Use Java serialization. This is meant to be really slow in Android (I'll profile it sometime). I'm worried about robustness when changes are made between versions however. Use something like JSON or XML. I'm not sure how I would cope with storing the dependencies between objects however. Would I have to give each object a unique ID and then use these IDs on loading to link the right objects together? I thought I could e.g. change the ChaseBehaviour to store a ID to an entity, instead of a reference, that would be used to look up the Entity before performing the behaviour. I'd rather avoid having to write lots of loading/saving code myself as I find it really easy to make mistakes (e.g. forgetting to save something, reading things out in the wrong order). Can anyone give me any tips on good formats to save to or class designs that make saving state easier?

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• When to delete newly deprecated code?

  - by John

  I spent a month writing an elaborate payment system that handles both credit card payments and electronic fund transfers. My work was used on production server for about a month. I was told recently by the client that he no longer wants to use the electronic fund transfer feature. Because the way I had to interface and communicate with the credit card gateway is drastically different from the electronic fund transfer api (eg. the cc company gives transaction responses immediately after an http request, while the eft company gives transaction responses 5 business days after an http request), I spent a lot of time writing my own API to abstract common function calls like function payment(amount, pay_method,pay_freq) function updateRecurringSchedule(user_id,new_schedule) etc.. Now that the client wants to abandon the EFT feature, all my work for this abstracted payments API is obsolete. I'm deliberating over whether I should scrap my work. Here's my pro vs. con for scrapping it now: PRO 1: Eliminate code bloat PRO 2: New developers do not need to learn MY API. They only need to read the CC company's API PRO 3: Because the EFT company did not handle recurring payment schedules, refunds, and validation, I wrote my own application to do it. Although the CC company's API permitted this functionality, I opted to use mine instead so that I could streamline my code. now that EFT is out of the picture, I can delete all this confusing code and just rely on the CC company's sytsem to manage recurring billing, payment schedules, refunds, validations etc... CON 1: Although I can just delete the EFT code, it still takes time to remove the entire framework consolidates different payment systems. CON 2: with regards to PRO 3, it takes time to build functionality that integrates the payment system more closely with the CC company. CON 3: I feel insecure deleting all this work. I don't think I'll ever use it again. But, for some inexplicable reason, I just don't feel comfortable deleting this work "right now". So my question is, should I delete one month's worth recent development? If yes, should I do it immediately or wait X amount of time before doing so?

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• hashing password giving different results

  - by geoff

  I am taking over a system that a previous developer wrote. The system has an administrator approve a user account and when they do that the system uses the following method to hash a password and save it to the database. It sends the unhashed password to the user. When the user logs in the system uses the exact same method to hash what the user enters and compares it to the database value. We've run into a couple of times when the database entry doesn't match the user's entry whey they should. So it appears that the method isn't always hashing the value the same. Does anyone know if this method of hashing isn't reliable and how to make it reliable? Thanks. private string HashPassword(string password) { string hashedPassword = string.Empty; // Convert plain text into a byte array. byte[] plainTextBytes = Encoding.UTF8.GetBytes(password); // Allocate array, which will hold plain text and salt. byte[] plainTextWithSaltBytes = new byte[plainTextBytes.Length + SALT.Length]; // Copy plain text bytes into resulting array. for(int i = 0; i < plainTextBytes.Length; i++) plainTextWithSaltBytes[i] = plainTextBytes[i]; // Append salt bytes to the resulting array. for(int i = 0; i < SALT.Length; i++) plainTextWithSaltBytes[plainTextBytes.Length + i] = SALT[i]; // Because we support multiple hashing algorithms, we must define // hash object as a common (abstract) base class. We will specify the // actual hashing algorithm class later during object creation. HashAlgorithm hash = new SHA256Managed(); // Compute hash value of our plain text with appended salt. byte[] hashBytes = hash.ComputeHash(plainTextWithSaltBytes); // Create array which will hold hash and original salt bytes. byte[] hashWithSaltBytes = new byte[hashBytes.Length + SALT.Length]; // Copy hash bytes into resulting array. for(int i = 0; i < hashBytes.Length; i++) hashWithSaltBytes[i] = hashBytes[i]; // Append salt bytes to the result. for(int i = 0; i < SALT.Length; i++) hashWithSaltBytes[hashBytes.Length + i] = SALT[i]; // Convert result into a base64-encoded string. hashedPassword = Convert.ToBase64String(hashWithSaltBytes); return hashedPassword; }

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• Java compiler rejects variable declaration with parameterized inner class

  - by Johansensen

  I have some Groovy code which works fine in the Groovy bytecode compiler, but the Java stub generated by it causes an error in the Java compiler. I think this is probably yet another bug in the Groovy stub generator, but I really can't figure out why the Java compiler doesn't like the generated code. Here's a truncated version of the generated Java class (please excuse the ugly formatting): @groovy.util.logging.Log4j() public abstract class AbstractProcessingQueue <T> extends nz.ac.auckland.digitizer.AbstractAgent implements groovy.lang.GroovyObject { protected int retryFrequency; protected java.util.Queue<nz.ac.auckland.digitizer.AbstractProcessingQueue.ProcessingQueueMember<T>> items; public AbstractProcessingQueue (int processFrequency, int timeout, int retryFrequency) { super ((int)0, (int)0); } private enum ProcessState implements groovy.lang.GroovyObject { NEW, FAILED, FINISHED; } private class ProcessingQueueMember<E> extends java.lang.Object implements groovy.lang.GroovyObject { public ProcessingQueueMember (E object) {} } } The offending line in the generated code is this: protected java.util.Queue<nz.ac.auckland.digitizer.AbstractProcessingQueue.ProcessingQueueMember<T>> items; which produces the following compile error: [ERROR] C:\Documents and Settings\Administrator\digitizer\target\generated-sources\groovy-stubs\main\nz\ac\auckland\digitizer\AbstractProcessingQueue.java:[14,96] error: improperly formed type, type arguments given on a raw type The column index of 96 in the compile error points to the <T> parameterization of the ProcessingQueueMember type. But ProcessingQueueMember is not a raw type as the compiler claims, it is a generic type: private class ProcessingQueueMember <E> extends java.lang.Object implements groovy.lang.GroovyObject { ... I am very confused as to why the compiler thinks that the type Queue<ProcessingQueueMember<T>> is invalid. The Groovy source compiles fine, and the generated Java code looks perfectly correct to me too. What am I missing here? Is it something to do with the fact that the type in question is a nested class? (in case anyone is interested, I have filed this bug report relating to the issue in this question) Edit: Turns out this was indeed a stub compiler bug- this issue is now fixed in 1.8.9, 2.0.4 and 2.1, so if you're still having this issue just upgrade to one of those versions. :)

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• Cannot extend a class located in another file, PHP

  - by NightMICU

  I am trying to set up a class with commonly used tasks, such as preparing strings for input into a database and creating a PDO object. I would like to include this file in other class files and extend those classes to use the common class' code. However, when I place the common class in its own file and include it in the class it will be used in, I receive an error that states the second class cannot be found. For example, if the class name is foo and it is extending bar (the common class, located elsewhere), the error says that foo cannot be found. But if I place the code for class bar in the same file as foo, it works. Here are the classes in question - Common Class abstract class coreFunctions { protected $contentDB; public function __construct() { $this->contentDB = new PDO('mysql:host=localhost;dbname=db', 'username', 'password'); } public function cleanStr($string) { $cleansed = trim($string); $cleansed = stripslashes($cleansed); $cleansed = strip_tags($cleansed); return $cleansed; } } Code from individual class include $_SERVER['DOCUMENT_ROOT'] . '/includes/class.core-functions.php'; $mode = $_POST['mode']; if (isset($mode)) { $gallery = new gallery; switch ($mode) { case 'addAlbum': $gallery->addAlbum($_POST['hash'], $_POST['title'], $_POST['description']); } } class gallery extends coreFunctions { private function directoryPath($string) { $path = trim($string); $path = strtolower($path); $path = preg_replace('/[^ \pL \pN]/', '', $path); $path = preg_replace('[\s+]', '', $path); $path = substr($path, 0, 18); return $path; } public function addAlbum($hash, $title, $description) { $title = $this->cleanStr($title); $description = $this->cleanStr($description); $path = $this->directoryPath($title); if ($title && $description && $hash) { $addAlbum = $this->contentDB->prepare("INSERT INTO gallery_albums (albumHash, albumTitle, albumDescription, albumPath) VALUES (:hash, :title, :description, :path)"); $addAlbum->execute(array('hash' => $hash, 'title' => $title, 'description' => $description, 'path' => $path)); } } } The error when I try it this way is Fatal error: Class 'gallery' not found in /home/opheliad/public_html/admin/photo-gallery/includes/class.admin_photo-gallery.php on line 10

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• C++ class member functions instantiated by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched Stack Overflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state information was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (VC++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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• Use multiple inheritance to discriminate useage roles?

  - by Arne

  Hi fellows, it's my flight simulation application again. I am leaving the mere prototyping phase now and start fleshing out the software design now. At least I try.. Each of the aircraft in the simulation have got a flight plan associated to them, the exact nature of which is of no interest for this question. Sufficient to say that the operator way edit the flight plan while the simulation is running. The aircraft model most of the time only needs to read-acess the flight plan object which at first thought calls for simply passing a const reference. But ocassionally the aircraft will need to call AdvanceActiveWayPoint() to indicate a way point has been reached. This will affect the Iterator returned by function ActiveWayPoint(). This implies that the aircraft model indeed needs a non-const reference which in turn would also expose functions like AppendWayPoint() to the aircraft model. I would like to avoid this because I would like to enforce the useage rule described above at compile time. Note that class WayPointIter is equivalent to a STL const iterator, that is the way point can not be mutated by the iterator. class FlightPlan { public: void AppendWayPoint(const WayPointIter& at, WayPoint new_wp); void ReplaceWayPoint(const WayPointIter& ar, WayPoint new_wp); void RemoveWayPoint(WayPointIter at); (...) WayPointIter First() const; WayPointIter Last() const; WayPointIter Active() const; void AdvanceActiveWayPoint() const; (...) }; My idea to overcome the issue is this: define an abstract interface class for each usage role and inherit FlightPlan from both. Each user then only gets passed a reference of the appropriate useage role. class IFlightPlanActiveWayPoint { public: WayPointIter Active() const =0; void AdvanceActiveWayPoint() const =0; }; class IFlightPlanEditable { public: void AppendWayPoint(const WayPointIter& at, WayPoint new_wp); void ReplaceWayPoint(const WayPointIter& ar, WayPoint new_wp); void RemoveWayPoint(WayPointIter at); (...) }; Thus the declaration of FlightPlan would only need to be changed to: class FlightPlan : public IFlightPlanActiveWayPoint, IFlightPlanEditable { (...) }; What do you think? Are there any cavecats I might be missing? Is this design clear or should I come up with somethink different for the sake of clarity? Alternatively I could also define a special ActiveWayPoint class which would contain the function AdvanceActiveWayPoint() but feel that this might be unnecessary. Thanks in advance!

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• Meshing different systems of keys together in XML Schema

  - by Tom W

  Hello SO, I'd like to ask people's thoughts on an XSD problem I've been pondering. The system I am trying to model is thus: I have a general type that represents some item in a hypothetical model. The type is abstract and will be inherited by all manner of different model objects, so the model is heterogeneous. Furthermore, some types exist only as children of other types. Objects are to be given an identifier, but the scope of uniqueness of this identifier varies. Some objects - we will call them P (for Parent) objects - must have a globally unique identifier. This is straightforward and can use the xs:key schema element. Other objects (we can call them C objects, for Child) are children of a P object and must have an identifier that is unique only in the scope of that parent. For example, object P1 has two children, object C1 and C2, and object P2 has one child, object C3. In this system, the identifiers given could be as follows: P1: 1 (1st P object globally) P2: 2 (2nd P object globally) C1: 1 (1st C object of P1) C2: 2 (2nd C object of P1) C3: 1 (1st C object of P2) I want the identity syntax of every model object to be identical if possible, therefore my first pass at implementing is to define a single type: <xs:complexType name="ModelElement"> <xs:attribute name="IDMode" type="IdentityMode"/> <xs:attribute name="Identifier" type="xs:string"/> </xs:complexType> where the IdentityMode is an enumerated value: <xs:simpleType name="IdentityMode"> <xs:restriction base="xs:string"> <xs:enumeration value="Identified"/> <xs:enumeration value="Indexed"/> <xs:enumeration value="None"/> </xs:restriction> </xs:simpleType> Here "Identified" signifies a global identifier, and "Indexed" indicates an identifier local only to the parent. My question is, how do I enforce these uniqueness conditions using unique, key or other schema elements based on the IdentityMode property of the given subtype of ModelElement?

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• Cannot .Count() on IQueryable (NHibernate)

  - by Bruno Reis

  Hello, I'm with an irritating problem. It might be something stupid, but I couldn't find out. I'm using Linq to NHibernate, and I would like to count how many items are there in a repository. Here is a very simplified definition of my repository, with the code that matters: public class Repository { private ISession session; /* ... */ public virtual IQueryable<Product> GetAll() { return session.Linq<Product>(); } } All the relevant code in the end of the question. Then, to count the items on my repository, I do something like: var total = productRepository.GetAll().Count(); The problem is that total is 0. Always. However there are items in the repository. Furthermore, I can .Get(id) any of them. My NHibernate log shows that the following query was executed: SELECT count(*) as y0_ FROM [Product] this_ WHERE not (1=1) That must be that "WHERE not (1=1)" clause the cause of this problem. What can I do to be able .Count() the items in my repository? Thanks! EDIT: Actually the repository.GetAll() code is a little bit different... and that might change something! It is actually a generic repository for Entities. Some of the entities implement also the ILogicalDeletable interface (it contains a single bool property "IsDeleted"). Just before the "return" inside the GetAll() method I check if if the Entity I'm querying implements ILogicalDeletable. public interface IRepository<TEntity, TId> where TEntity : Entity<TEntity, TId> { IQueryable<TEntity> GetAll(); ... } public abstract class Repository<TEntity, TId> : IRepository<TEntity, TId> where TEntity : Entity<TEntity, TId> { public virtual IQueryable<TEntity> GetAll() { if (typeof (ILogicalDeletable).IsAssignableFrom(typeof (TEntity))) { return session.Linq<TEntity>() .Where(x => (x as ILogicalDeletable).IsDeleted == false); } else { return session.Linq<TEntity>(); } } } public interface ILogicalDeletable { bool IsDeleted {get; set;} } public Product : Entity<Product, int>, ILogicalDeletable { ... } public IProductRepository : IRepository<Product, int> {} public ProductRepository : Repository<Product, int>, IProductRepository {} Edit 2: actually the .GetAll() is always returning an empty result-set for entities that implement the ILogicalDeletable interface (ie, it ALWAYS add a WHERE NOT (1=1) clause. I think Linq to NHibernate does not like the typecast.

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• How to pipe two CORE::system commands in a cross-platform way

  - by Pedro Silva

  I'm writing a System::Wrapper module to abstract away from CORE::system and the qx operator. I have a serial method that attempts to connect command1's output to command2's input. I've made some progress using named pipes, but POSIX::mkfifo is not cross-platform. Here's part of what I have so far (the run method at the bottom basically calls system): package main; my $obj1 = System::Wrapper->new( interpreter => 'perl', arguments => [-pe => q{''}], input => ['input.txt'], description => 'Concatenate input.txt to STDOUT', ); my $obj2 = System::Wrapper->new( interpreter => 'perl', arguments => [-pe => q{'$_ = reverse $_}'}], description => 'Reverse lines of input input', output => { '>' => 'output' }, ); $obj1->serial( $obj2 ); package System::Wrapper; #... sub serial { my ($self, @commands) = @_; eval { require POSIX; POSIX->import(); require threads; }; my $tmp_dir = File::Spec->tmpdir(); my $last = $self; my @threads; push @commands, $self; for my $command (@commands) { croak sprintf "%s::serial: type of args to serial must be '%s', not '%s'", ref $self, ref $self, ref $command || $command unless ref $command eq ref $self; my $named_pipe = File::Spec->catfile( $tmp_dir, int \$command ); POSIX::mkfifo( $named_pipe, 0777 ) or croak sprintf "%s::serial: couldn't create named pipe %s: %s", ref $self, $named_pipe, $!; $last->output( { '>' => $named_pipe } ); $command->input( $named_pipe ); push @threads, threads->new( sub{ $last->run } ); $last = $command; } $_->join for @threads; } #... My specific questions: Is there an alternative to POSIX::mkfifo that is cross-platform? Win32 named pipes don't work, as you can't open those as regular files, neither do sockets, for the same reasons. The above doesn't quite work; the two threads get spawned correctly, but nothing flows across the pipe. I suppose that might have something to do with pipe deadlocking or output buffering. What throws me off is that when I run those two commands in the actual shell, everything works as expected.

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• Dynamic swappable Data Access Layer

  - by Andy

  I'm writing a data driven WPF client. The client will typically pull data from a WCF service, which queries a SQL db, but I'd like the option to pull the data directly from SQL or other arbitrary data sources. I've come up with this design and would like to hear your opinion on whether it is the best design. First, we have some data object we'd like to extract from SQL. // The Data Object with a single property public class Customer { private string m_Name = string.Empty; public string Name { get { return m_Name; } set { m_Name = value;} } } Then I plan on using an interface which all data access layers should implement. Suppose one could also use an abstract class. Thoughts? // The interface with a single method interface ICustomerFacade { List<Customer> GetAll(); } One can create a SQL implementation. // Sql Implementation public class SqlCustomrFacade : ICustomerFacade { public List<Customer> GetAll() { // Query SQL db and return something useful // ... return new List<Customer>(); } } We can also create a WCF implementation. The problem with WCF is is that it doesn't use the same data object. It creates its own local version, so we would have to copy the details over somehow. I suppose one could use reflection to copy the values of similar fields across. Thoughts? // Wcf Implementation public class WcfCustomrFacade : ICustomerFacade { public List<Customer> GetAll() { // Get date from the Wcf Service (not defined here) List<WcfService.Customer> wcfCustomers = wcfService.GetAllCustomers(); // The list we're going to return List<Customer> customers = new List<Customer>(); // This is horrible foreach(WcfService.Customer wcfCustomer in wcfCustomers) { Customer customer = new Customer(); customer.Name = wcfCustomer.Name; customers.Add(customer); } return customers; } } I also plan on using a factory to decide which facade to use. // Factory pattern public class FacadeFactory() { public static ICustomerFacade CreateCustomerFacade() { // Determine the facade to use if (ConfigurationManager.AppSettings["DAL"] == "Sql") return new SqlCustomrFacade(); else return new WcfCustomrFacade(); } } This is how the DAL would typically be used. // Test application public class MyApp { public static void Main() { ICustomerFacade cf = FacadeFactory.CreateCustomerFacade(); cf.GetAll(); } } I appreciate your thoughts and time.

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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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