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• Value objects in DDD - Why immutable?

  - by Hobbes

  I don't get why value objects in DDD should be immutable, nor do I see how this is easily done. (I'm focusing on C# and Entity Framework, if that matters.) For example, let's consider the classic Address value object. If you needed to change "123 Main St" to "123 Main Street", why should I need to construct a whole new object instead of saying myCustomer.Address.AddressLine1 = "123 Main Street"? (Even if Entity Framework supported structs, this would still be a problem, wouldn't it?) I understand (I think) the idea that value objects don't have an identity and are part of a domain object, but can someone explain why immutability is a Good Thing? EDIT: My final question here really should be "Can someone explain why immutability is a Good Thing as applied to Value Objects?" Sorry for the confusion! EDIT: To clairfy, I am not asking about CLR value types (vs reference types). I'm asking about the higher level DDD concept of Value Objects. For example, here is a hack-ish way to implement immutable value types for Entity Framework: http://rogeralsing.com/2009/05/21/entity-framework-4-immutable-value-objects. Basically, he just makes all setters private. Why go through the trouble of doing this?

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• Linq to sql Repository pattern , Some doubts

  - by MindlessProgrammer

  I am using repository pattern with linq to sql, I am using a repository class per table. I want to know , am i doing at good/standard way, ContactRepository Contact GetByID() Contact GetAll() COntactTagRepository List<ContactTag> Get(long contactID) List<ContactTag> GetAll() List<ContactTagDetail> GetAllDetails() class ContactTagDetail { public Contact Contact {get;set;} public ContactTag COntactTag {get;set;} } When i need a contact i call method in contactrepository, same for contacttag but when i need contact and tags together i call GetDetais() in ContactTag repository its not returning the COntactTag entity generated by the orm insted its returning ContactTagDetail entity conatining both COntact and COntactTag generated by the orm, i know i can simple call GetAll in COntactTag repository and can access Contact.ContactTag but as its linq to sql it will there is no option to Deferred Load in query level, so whenever i need a entity with a related entity i create a projection class Another doubt is where i really need to right the method i can do it in both contact & ContactTag repostitory like In contact repository GetALlWithTags() or something but i am doing it in in COntactTag repository Whats your suggestions ?

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• coredata using old file version on device

  - by Martin KS

  This is a follow on from my previous problems here. Resetting the simulator solved all my troubles before, and I've gone on to complete my App. I now have the exact same problem when installing the app onto my iPhone device. It picks up an old version of my database, which doesn't have the second entity in it, and crashes when I try to access the second entity: 2010-04-22 23:52:18.860 albumCloud[135:207] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '+entityForName: could not locate an NSManagedObjectModel for entity name 'Image'' 2010-04-22 23:52:18.874 albumCloud[135:207] Stack: ( 843263261, 825818644, 820669213, 20277, 844154820, 16985, 14633, 844473760, 844851728, 862896011, 843011267, 843009055, 860901832, 843738160, 843731504, 11547, 11500 ) terminate called after throwing an instance of 'NSException' I have two questions: 1) How on earth do I delete my app thoroughly enough from my phone that it removes the old data? (I've so far tried regular app deletion, deleting and then holding home and power for a reboot, cursing at and threatening the app while running it... everything) 2) How do I prevent this happening when my application is in the App store, and I for some reason decide that I want to add another entity to the store, or another attribute to the existing entities? is there an "if x doesn't exist then create it" method?

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• Is this a hole in dynamic binding in C# 4?

  - by Galilyou

  I've seen a very interesting post on Fabio Maulo's blog. Here's the code and the bug if you don't want to jump to the url. I defined a new generic class like so: public class TableStorageInitializer<TTableEntity> where TTableEntity : class, new() { public void Initialize() { InitializeInstance(new TTableEntity()); } public void InitializeInstance(dynamic entity) { entity.PartitionKey = Guid.NewGuid().ToString(); entity.RowKey = Guid.NewGuid().ToString(); } } Note that InitializeInstance accepts one parameter, which is of type dynamic. Now to test this class, I defined another class that is nested inside my main Program class like so: class Program { static void Main(string[] args) { TableStorageInitializer<MyClass> x = new TableStorageInitializer<MyClass>(); x.Initialize(); } private class MyClass { public string PartitionKey { get; set; } public string RowKey { get; set; } public DateTime Timestamp { get; set; } } } Note: the inner class "MyClass" is declared private. Now if i run this code I get a "Microsoft.CSharp.RuntimeBinder.RuntimeBinderException" on the line "entity.PartitionKey = Guide.NewGuid().ToString()". The interesting part, though is that the message of the exception says "Object doesn't contain a definition for PartitionKey". Also note that if you changed the modifier of the nested class to public, the code will execute with no problems. So what do you guys think is really happening under the hood? Please refer to any documentation -of course if this is documented anywhere- that you may find?

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• Hibernate: Querying objects by attributes of inherited classes

  - by MichaelD

  Hi all, I ran into a problem with Hibernate concerning queries on classes which use inheritance. Basically I've the following class hierarchy: @Entity @Table( name = "recording" ) class Recording { ClassA attributeSet; ... } @Entity @Inheritance( strategy = InheritanceType.JOINED ) @Table( name = "classA" ) public class ClassA { String Id; ... } @Entity @Table( name = "ClassB1" ) @PrimaryKeyJoinColumn( name = "Id" ) public class ClassB1 extends ClassA { private Double P1300; private Double P2000; } @Entity @Table( name = "ClassB2" ) @PrimaryKeyJoinColumn( name = "Id" ) public class ClassB2 extends ClassA { private Double P1300; private Double P3000; } The hierarchy is already given like this and I cannot change it easily. As you can see ClassB1 and ClassB2 inherit from ClassA. Both classes contain a set of attributes which sometimes even have the same names (but I can't move them to ClassA since there are possible more sub-classes which do not use them). The Recording class references one instance of one of this classes. Now my question: What I want to do is selecting all Recording objects in my database which refer to an instance of either ClassB1 or ClassB2 with e.g. the field P1300 == 15.5 (so this could be ClassB1 or ClassB2 instances since the P1300 attribute is declared in both classes). What I tried is something like this: Criteria criteria = session.createCriteria(Recording.class); criteria.add( Restrictions.eq( "attributeSet.P1300", new Double(15.5) ) ); criteria.list(); But since P1300 is not an attribute of ClassA hibernate throws an exception telling me: could not resolve property: P1300 of: ClassA How can I tell hibernate that it should search in all subclasses to find the attribute I want to filter? Thanks MichaelD

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• Unable to persist objects in GAE JDO

  - by Basil Dsouza

  Hello Guys, I am completely fresh to both JDO and GAE, and have been struggling to get my data layer to persist any code at all! The issues I am facing may be very simple, but I just cant seem to find any a way no matter what solution I try. Firstly the problem: (Slightly simplified, but still contains all the info necessary) My data model is as such: User: (primary key) String emailID String firstName Car: (primary key) User user (primary key) String registration String model This was the initial datamodel. I implemented a CarPK object to get a composite primary key of the User and the registration. However that ran into a variety of issues. (Which i will save for another time/question) I then changed the design as such: User: (Unchanged) Car: (primary key) String fauxPK (here fauxPK = user.getEmailID() + SEP + registration) User user String registration String model This works fine for the user, and it can insert and retrieve user objects. However when i try to insert a Car Object, i get the following error: "Cannot have a java.lang.String primary key and be a child object" Found the following helpful link about it: http://stackoverflow.com/questions/2063467/persist-list-of-objects Went to the link suggested there, that explains how to create Keys, however they keep talking about "Entity Groups" and "Entity Group Parents". But I cant seem to find any articles or sites that explain what are "Entity Group"s or an "Entity Group Parents" I could try fiddling around some more to figure out if i can store an object somehow, But I am running sort on patience and also would rather understand and implement than vice versa. So i would appreciate any docs (even if its huge) that covers all these points, and preferably has some examples that go beyond the very basic data modeling. And thanks for reading such a long post :)

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• ManyToOne annotation fails with Hibernate 4.1: MappingException

  - by barelas

  Using Hibernate 4.1.1.Final. When I try to add @ManyToOne, schema creation fails with: org.hibernate.MappingException: Could not instantiate persister org.hibernate.persister.entity.SingleTableEntityPersister User.java: @Entity public class User { @Id private int id; public int getId() {return id;} public void setId(int id) {this.id = id;} @ManyToOne Department department; public Department getDepartment() {return department;} public void setDepartment(Department department) {this.department = department;} } Department.java @Entity public class Department { @Id private int departmentNumber; public int getDepartmentNumber() {return departmentNumber;} public void setDepartmentNumber(int departmentNumber) {this.departmentNumber = departmentNumber;} } hibernate.properties: hibernate.connection.driver_class=com.mysql.jdbc.Driver hibernate.connection.url=jdbc:mysql://localhost:3306/dbname hibernate.connection.username=user hibernate.connection.password=pass hibernate.connection.pool_size=5 hibernate.dialect=org.hibernate.dialect.MySQL5InnoDBDialect hibernate.hbm2ddl.auto=create init (throwing exception): ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().buildServiceRegistry(); sessionFactory = new MetadataSources( serviceRegistrY.addAnnotatedClass(Department.class).addAnnotatedClass(User.class).buildMetadata().buildSessionFactory(); exception throwed at init: org.hibernate.MappingException: Could not instantiate persister org.hibernate.persister.entity.SingleTableEntityPersister at org.hibernate.persister.internal.PersisterFactoryImpl.create(PersisterFactoryImpl.java:174) at org.hibernate.persister.internal.PersisterFactoryImpl.createEntityPersister(PersisterFactoryImpl.java:148) at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:820) at org.hibernate.metamodel.source.internal.SessionFactoryBuilderImpl.buildSessionFactory(SessionFactoryBuilderImpl.java:65) at org.hibernate.metamodel.source.internal.MetadataImpl.buildSessionFactory(MetadataImpl.java:340) I have tried adding some other annotations, but shouldn't the defaults work and create the tables and foreign key? If I remove the department from User, tables get generated fine. Thanks in advance!

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• How to specialize template for type derived from particular type

  - by relaxxx

  I have class World which manages creation of object... After creation it calls afterCreation method and I the created object is user-defined type derived from Entity (eg. MyEntity), I want to call addEntity. I the object was something else, I want to do nothing. addEntity must be called with appropriate T, because it generates unique IDs for every derived class etc. Here is my solution: template <int v> struct ToType { enum { value = v }; }; template <typename T> void World::afterCreation(T * t) { afterCreation(t, ToType<std::is_base_of<Entity, T>::value>()); } template <typename T> void World::afterCreation(T * t, ToType<true>) { addEntity(t); //here I cant pass Entity *, I need the real type, eg. MyEntity } template <typename T> void World::afterCreation(T * t, ToType<false>) { } My question is - Can in be done better way? How can I simulate following code without ToType or similar? template <typename T> void afterCreation(){/*generic impl*/} template <typename T where T is derived from Entity> void afterCreation(){/*some specific stuff*/} "specialize" in the title is only to describe my intention, no need to solve problem with template specialization

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• Just need someone familiar with HTTPClient to check over a piece of code

  - by jax

  here are two little helper methods I have made for downloading files. I have had to mix and match different tutorials of the web to get what I have here. Now is there anything that I have done blatantly wrong here? public static InputStream simplePostRequest(URL url, List<NameValuePair> postData) throws ClientProtocolException, IOException { DefaultHttpClient httpclient = new DefaultHttpClient(); HttpPost postMethod=new HttpPost(url.toExternalForm()); postMethod.setEntity(new UrlEncodedFormEntity(postData, HTTP.UTF_8)); HttpResponse response = httpclient.execute(postMethod); HttpEntity entity = response.getEntity(); return entity.getContent(); } public static InputStream simpleGetRequest(URL url, List<NameValuePair> queryString) throws ClientProtocolException, IOException { Uri.Builder uri = new Uri.Builder(); uri.path(url.getPath()); for(NameValuePair nvp: queryString) { uri.appendQueryParameter(nvp.getName(), nvp.getValue()); } DefaultHttpClient httpClient = new DefaultHttpClient(); HttpHost host = new HttpHost(url.getHost()); HttpResponse response = httpClient.execute(host, new HttpGet(uri.build().toString())); HttpEntity entity = response.getEntity(); return entity.getContent(); }

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• LINQ - Querying a list filtered via a Many-to-Many reltionship

  - by user118190

  Please excuse the context of my question for I did not know how to exactly word it. To not complicate things further, here's my business requirement: "bring me back all the Employees where they belong in Department "X". So when I view this, it will display all of the Employees that belong to this Department. Here's my environment: Silverlight 3 with Entity Framework 1.0 and WCF Data Services 1.0. I am able to load and bind all kinds of lists (simple), no problem. I don't feel that my environment matters and that's why I feel it is a LINQ question more than the technologies. My question is for scenarios where I have 3 tables linked, i.e. entities (collections). For example, I have this in my EDM: Employee--EmployeeProject--Project. Here's the table design from the Database: Employee (table1) ------------- EmployeeID (PK) FirstName other Attributes ... EmployeeProject (table2) ------------- EmployeeProjectID (PK) EmployeeID (FK) ProjectID (FK) AssignedDate other Attributes ... Project (table3) ------------- ProjectID (PK) Name other Attributes ... Here's the EDM design from Entity Framework: ------------------------ Employee (entity1) ------------------------ (Scalar Properties) ------------------- EmployeeID (PK) FirstName other Attributes ... ------------------- (Navigation Properties) ------------------- EmployeeProjects ------------------------ EmployeeProject (entity2) ------------------------ (Scalar Properties) ------------------- EmployeeProjectID (PK) AssignedDate other Attributes ... ------------------- (Navigation Properties) ------------------- Employee Project ------------------------ Project (entity3) ------------------------ (Scalar Properties) ------------------- ProjectID (PK) Name other Attributes ... ------------------- (Navigation Properties) ------------------- EmployeeProjects So far, I have only been able to do: var filteredList = Context.Employees .Where(e => e.EmployeeProjects.Where(ep => ep.Project.Name == "ProjectX")) NOTE: I have updated the syntax of the query after John's post. As you can see, I can only query, the related entity (EmployeeProjects). All I want is being able to filter to Project from the Employee entity. Thanks for any advice.

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• Weak hashmap with weak references to the values?

  - by Razor Storm

  I am building an android app where each entity has a bitmap that represents its sprite. However, each entity can be be duplicated (there might be 3 copies of entity asdf for example). One approach is to load all the sprites upfront, and then put the correct sprite in the constructors of the entities. However, I want to decode the bitmaps lazily, so that the constructors of the entities will decode the bitmaps. The only problem with this is that duplicated entities will load the same bitmap twice, using 2x the memory (Or n times if the entity is created n times). To fix this, I built a SingularBitmapFactory that will store a decoded Bitmap into a hash, and if the same bitmap is asked for again, will simply return the previously hashed one instead of building a new one. Problem with this, though, is that the factory holds a copy of all bitmaps, and so won't ever get garbage collected. What's the best way to switch the hashmap to one with weakly referenced values? In otherwords, I want a structure where the values won't be GC'd if any other object holds a reference to it, but as long as no other objects refers it, then it can be GC'd.

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• how to merge ecommerce transaction data between two databases

  - by yamspog

  We currently run an ecommerce solution for a leisure and travel company. Everytime we have a release, we must bring the ecommerce site down as we update database schema and the data access code. We are using a custom built ORM where each data entity is responsible for their own CRUD operations. This is accomplished by dynamically generating the SQL based on attributes in the data entity. For example, the data entity for an address would be... [tableName="address"] public class address : dataEntity { [column="address1"] public string address1; [column="city"] public string city; } So, if we add a new column to the database, we must update the schema of the database and also update the data entity. As you can expect, the business people are not too happy about this outage as it puts a crimp in their cash-flow. The operations people are not happy as they have to deal with a high-pressure time when database and applications are upgraded. The programmers are upset as they are constantly getting in trouble for the legacy system that they inherited. Do any of you smart people out there have some suggestions?

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• Retrieve only the superclass from a class hierarchy

  - by user1792724

  I have an scenario as the following: @Entity @Table(name = "ANIMAL") @Inheritance(strategy = InheritanceType.JOINED) public class Animal implements Serializable { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "S_ANIMAL") @SequenceGenerator(name = "S_ANIMAL", sequenceName = "S_ANIMAL", allocationSize = 1) public int getNumero() { return numero; } public void setNumero(int numero) { this.numero = numero; } . . . } and as the subclass: @Entity @Table(name = "DOG") public class Dog extends Animal { private static final long serialVersionUID = -7341592543130659641L; . . . } I have a JPA Select statement like this: SELECT a FROM Animal a; I'm using Hibernate 3.3.1 As I can see the framework retrieves instances of Animal and also of Dog using a left outer join. Is there a way to Select only the "part" Animal? I mean, the previous Select will get all the Animals, those that are only Animals but not Dogs and those that are Dogs. I want them all, but in the case of Dogs I want to only retrieve the "Animal part" of them. I found the @org.hibernate.annotations.Entity(polymorphism = PolymorphismType.EXPLICIT) but as I could see this only works if Animal isn't an @Entity. Thanks a lot.

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• What is the purpose of unit testing an interface repository

  - by ahsteele

  I am unit testing an ICustomerRepository interface used for retrieving objects of type Customer. As a unit test what value am I gaining by testing the ICustomerRepository in this manner? Under what conditions would the below test fail? For tests of this nature is it advisable to do tests that I know should fail? i.e. look for id 4 when I know I've only placed 5 in the repository I am probably missing something obvious but it seems the integration tests of the class that implements ICustomerRepository will be of more value. [TestClass] public class CustomerTests : TestClassBase { private Customer SetUpCustomerForRepository() { return new Customer() { CustId = 5, DifId = "55", CustLookupName = "The Dude", LoginList = new[] { new Login { LoginCustId = 5, LoginName = "tdude" }, new Login { LoginCustId = 5, LoginName = "tdude2" } } }; } [TestMethod] public void CanGetCustomerById() { // arrange var customer = SetUpCustomerForRepository(); var repository = Stub<ICustomerRepository>(); // act repository.Stub(rep => rep.GetById(5)).Return(customer); // assert Assert.AreEqual(customer, repository.GetById(5)); } } Test Base Class public class TestClassBase { protected T Stub<T>() where T : class { return MockRepository.GenerateStub<T>(); } } ICustomerRepository and IRepository public interface ICustomerRepository : IRepository<Customer> { IList<Customer> FindCustomers(string q); Customer GetCustomerByDifID(string difId); Customer GetCustomerByLogin(string loginName); } public interface IRepository<T> { void Save(T entity); void Save(List<T> entity); bool Save(T entity, out string message); void Delete(T entity); T GetById(int id); ICollection<T> FindAll(); }

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• how to minimize application downtime when updating database and application ORM

  - by yamspog

  We currently run an ecommerce solution for a leisure and travel company. Everytime we have a release, we must bring the ecommerce site down as we update database schema and the data access code. We are using a custom built ORM where each data entity is responsible for their own CRUD operations. This is accomplished by dynamically generating the SQL based on attributes in the data entity. For example, the data entity for an address would be... [tableName="address"] public class address : dataEntity { [column="address1"] public string address1; [column="city"] public string city; } So, if we add a new column to the database, we must update the schema of the database and also update the data entity. As you can expect, the business people are not too happy about this outage as it puts a crimp in their cash-flow. The operations people are not happy as they have to deal with a high-pressure time when database and applications are upgraded. The programmers are upset as they are constantly getting in trouble for the legacy system that they inherited. Do any of you smart people out there have some suggestions?

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• Managing Many to Many relationships in asp.net Wizard Control

  - by Luis

  Say I have this entity with a lot of attributes. In the input form I have decided to implement a wizard control so I can collect information about this entity in several steps. The problem is that I need to collect information that has been modeled has many to many relationships. I am planning to use a telerik gridview to manage this (add/edit/delete), the problem is where do I store that data since the entity in a insert form is not created on the database yet. OK so I can store all that info in temporary lists residing in the viewstate, waiting for the final submit where I dump all that in the DB, but one of the steps I am collecting files...now storing files in the viewstate is out of the question, same as as storing them in the session... I have been thinking of implementing in a way that the user has to submit some info first (say first 3 steps), commit the data to the database creating the parent entity and then start inserting all the childs entities...but this will get weird as it's confusing since on the first steps you not saving the data to the DB and on the next ones you are commiting directly... Anyone has any thoughts on this? Thanks

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• Effective communication in a component-based system

  - by Tesserex

  Yes, this is another question about my game engine, which is coming along very nicely, with much thanks to you guys. So, if you watched the video (or didn't), the objects in the game are composed of various components for things like position, sprites, movement, collision, sounds, health, etc. I have several message types defined for "tell" type communication between entities and components, but this only goes so far. There are plenty of times when I just need to ask for something, for example an entity's position. There are dozens of lines in my code that look like this: SomeComponent comp = (SomeComponent)entity.GetComponent(typeof(SomeComponent)); if (comp != null) comp.GetSomething(); I know this is very ugly, and I know that casting smells of improper OO design. But as complex as things are, there doesn't seem to be a better way. I could of course "hard-code" my component types and just have SomeComponent comp = entity.GetSomeComponent(); but that seems like a cop-out, and a bad one. I literally JUST REALIZED, while writing this, after having my code this way for months with no solution, that a generic will help me. SomeComponent comp = entity.GetComponent<SomeComponent>(); Amazing how that works. Anyway, this is still only a semantic improvement. My questions remain. Is this actually that bad? What's a better alternative?

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• JPA returning null for deleted items from a set

  - by Jon

  This may be related to my question from a few days ago, but I'm not even sure how to explain this part. (It's an entirely different parent-child relationship.) In my interface, I have a set of attributes (Attribute) and valid values (ValidValue) for each one in a one-to-many relationship. In the Spring MVC frontend, I have a page for an administrator to edit these values. Once it's submitted, if any of these fields (as <input> tags) are blank, I remove the ValidValue object like so: Set<ValidValue> existingValues = new HashSet<ValidValue>(attribute.getValidValues()); Set<ValidValue> finalValues = new HashSet<ValidValue>(); for(ValidValue validValue : attribute.getValidValues()) { if(!validValue.getValue().isEmpty()) { finalValues.add(validValue); } } existingValues.removeAll(finalValues); for(ValidValue removedValue : existingValues) { getApplicationDataService().removeValidValue(removedValue); } attribute.setValidValues(finalValues); getApplicationDataService().modifyAttribute(attribute); The problem is that while the database is updated appropriately, the next time I query for the Attribute objects, they're returned with an extra entry in their ValidValue set -- a null, and thus, the next time I iterate through the values to display, it shows an extra blank value in the middle. I've confirmed that this happens at the point of a merge or find, at the point of "Execute query ReadObjectQuery(entity.Attribute). Here's the code I'm using to modify the database (in the ApplicationDataService): public void modifyAttribute(Attribute attribute) { getJpaTemplate().merge(attribute); } public void removeValidValue(ValidValue removedValue) { ValidValue merged = getJpaTemplate().merge(removedValue); getJpaTemplate().remove(merged); } Here are the relevant parts of the entity classes: Entity @Table(name = "attribute") public class Attribute { @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "attribute") private Set<ValidValue> validValues = new HashSet<ValidValue>(0); } @Entity @Table(name = "valid_value") public class ValidValue { @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "attr_id", nullable = false) private Attribute attribute; }

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• Looking for Simplified Overview of EJB3

  - by sdoca

  Hi I'm looking for a simplified overview of EJB3 components. I seem to understand most of the pieces of the puzzle, but can't quite get them to fit together in my brain as a full picture. I've developed numerous web applications (wars) that have been deployed on Tomcat before, but not a full-fledged EE application (ear). I would like the overview to be as generic as possible. I'm not looking for a tutorial on how to set up EJB3 on Glassfish built in NetBeans or some other vendor specific tutorial that's more about the IDE than the technology. I keep reading about Java, ejb-jar, web and ear modules but am not clear on what these different modules contain and how to use them to put together my app. In my case, I want to write a simple database CRUD web application. The first step is simple; create entity classes that model the database tables my app will be using. I plan on using annotations. Should I create a jar that contains just these enity classes? Is this the ejb-jar module (sometimes referred to as the Java module)? Next, I'll need some business logic classes that make use of the entity classes. These are the session beans (stateless or stateful) correct? Should these be packaged in the same jar as the entity classes or a separate jar? Finally, I'll need some sort of web interface (I'll be creating a JSF portlet) application that makes use of the both the session and entity beans. Together with the above jar(s), this will be my war? Assuming the above to be correct, what is involved in creating an ear? Forgive me if this post is vague, but I'm having a hard time defining what it is I don't understand. Thanks for any help!

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• Oddities in Linq-to-SQL generated code related to property change/changing events

  - by Lasse V. Karlsen

  I'm working on creating my own Linq-to-Sql generated classes in order to learn the concepts behind it all. I have some questions, if anyone knows the answer to one or more of these I'd be much obliged. The code below, and thus the questions, are from looking at code generated by creating a .DBML file in the Visual Studio 2010 designer, and inspecting the .Designer.cs file afterwards. 1. Why is INotifyPropertyChanging not passing the property name The event raising method is defined like this: protected virtual void SendPropertyChanging() Why isn't the name of the property that is changing passed to the event here? It is defined to be part of the EventArgs descendant that is passed to the event handler, but the method only passes an empty such value to it. 2. Why are the EntitySet<X> attach/detach methods not raising property changed? For an EntitySet<X> reference, the following two methods are generated: private void attach_EmailAddress1s(EmailAddress1 entity) { this.SendPropertyChanging(); entity.Person1 = this; } private void detach_EmailAddress1s(EmailAddress1 entity) { this.SendPropertyChanging(); entity.Person1 = null; } Why isn't SendPropertyChanged also called here? I'm sure I have more questions later, but for now these will suffice :)

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• where is the best palce to count the lazy load property using JPA

  - by Ke

  Let's say we have a "Question" and "Answer" entity, @Entity public class Question extends IdEntity { @Lob private String content; @Transient private int answerTotal; @OneToMany(fetch = FetchType.LAZY) private List<Answer> answers = new ArrayList<Answer>(); ...... I need to tell how many answers for the question every time Question is queryed. So I need to do count: String count = "select count(o) from Answer o WHERE o.question=:q"; My question is, where is the best place to do the count? (Because I did a lot of query about Question entity, by date, by tag, by category, by asker, etc. It is obviously not a good solution to add count operation in each query. My first attempt is to implement a @PostLoad listener, so every time Question entity is loaded, I do count. However, EntityManager cannot be injected in listener. So this way does not work. Any hint?

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• Using an unencoded key vs a real Key, benefits?

  - by user246114

  Hi, I am reading the docs for Key generation in app engine. I'm not sure what effect using a simple String key has over a real Key. For example, when my users sign up, they must supply a unique username: class User { /** Key type = unencoded string. */ @PrimaryKey private String name; } now if I understand the docs correctly, I should still be able to generate named keys and entity groups using this, right?: // Find an instance of this entity: User user = pm.findObjectById(User.class, "myusername"); // Create a new obj and put it in same entity group: Key key = new KeyFactory.Builder( User.class.getSimpleName(), "myusername") .addChild(Goat.class.getSimpleName(), "baa").getKey(); Goat goat = new Goat(); goat.setKey(key); pm.makePersistent(goat); the Goat instance should now be in the same entity group as that User, right? I mean there's no problem with leaving the User's primary key as just the raw String? Is there a performance benefit to using a Key though? Should I update to: class User { /** Key type = unencoded string. */ @PrimaryKey private Key key; } // Generate like: Key key = KeyFactory.createKey( User.class.getSimpleName(), "myusername"); user.setKey(key); it's almost the same thing, I'd still just be generating the Key using the unique username anyway, Thanks

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• Synfony2 validation changes invalid integer to 0

  - by Craig

  I've added validation to a form and found that in some cases it is losing the invalid data I am feeding it and saving 0s instead. The output at the bottom shows that if I post the latitude as 'zzzzzz' (clearly not a number nor between -90 and 90) the form is declared as valid and saved with the value 0 How can that happen given that I have declared the input must be a number? ProxyType.php buildForm() $builder ->add('siteName', null, array('label' => 'Site name')) .... ->add('latitude', 'number', array('label' => 'Latitude')) ->add('longitude', 'number', array('label' => 'Longitude')) .... ; ProxyController.php createAction .... $postData = $request->request->get('niwa_pictbundle_proxytype'); $this->get('logger')->info('Posted latitude = '.$postData['latitude']); $form = $this->createForm(new ProxyType(), $entity); $form->bindRequest($request); if ($form->isValid()) { $this->get('logger')->info('Form declared valid : latlong ('.$entity->getLatitude().','.$entity->getLongitude().')'); .... validation.yml Acme\PictBundle\Entity\Proxy: properties: longitude: - Min: { limit: -180 } - Max: { limit: 180 } latitude: - Max: { limit: 90 } - Min: { limit: -90 } Output [2012-09-28 02:05:30] app.INFO: Posted latitude = zzzzzz [] [] [2012-09-28 02:05:30] app.INFO: Form declared valid : latlong (0,0) [] []

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• What is the best way to create a running integer id on the AppEngine data storage?

  - by Freed

  For various reasons, I need a unique running integer id for my entities stored on the Google AppEngine. The automatically generated key sort of has this behaviour, but it doesn't start from 1 (or 0) and doesn't guarantee that the generated integer part will come from a continuous sequence. What would be the best way to efficiently implement this on AppEngine? Is there any support from the storage system? To add to the complexity, I might need to do this over entities from different entity groups, meaning I can't just get the highest id right now and save an entity with the next id in a transaction. Might memcache be the way to go..? Edit: I havn't yet implemented this, but to clarify on the memcache idea. I know memcache is unreliable, but in practice it probably won't lose data "too often" to hurt performance. Basically, I would have a memcache entry for the last used id, update it (somehow atomically) whenever I create a new entity and use that id. In the case of memcache not having a value for this entry, I'd get the highest id so far by doing a query on my entities sorted by the id and update memcache (unless someone else had already done so). The only problem I can see with this right now would be atomicity of the operation as a whole if the save of my new entity was also part of a transaction. Thoughts..?

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• Hibernate many-to-many relationship

  - by Capitan

  I have two mapped types, related many-to-many. @Entity @Table(name = "students") public class Student{ ... @ManyToMany(fetch = FetchType.EAGER) @JoinTable( name = "students2courses", joinColumns = { @JoinColumn( name = "student_id", referencedColumnName = "_id") }, inverseJoinColumns = { @JoinColumn( name = "course_id", referencedColumnName = "_id") }) public Set<Course> getCourses() { return courses; } public void setCourses(Set<Course> courses) { this.courses = courses; } ... } __ @Entity @Table(name = "courses") public class Course{ ... @ManyToMany(fetch = FetchType.EAGER, mappedBy = "courses") public Set<Student> getStudents() { return students; } public void setStudents(Set<Student> students) { this.students = students; } ... } But if I update/delete Course entity, records are not created/deleted in table students2courses. (with Student entity updating/deleting goes as expected) I wrote abstract class HibObject public abstract class HibObject { public String getRemoveMTMQuery() { return null; } } which is inherited by Student and Course. In DAO I added this code (for delete() method): String query = obj.getRemoveMTMQuery(); if (query != null) { session.createSQLQuery(query).executeUpdate(); } and I ovrerided method getRemoveMTMQuery() for Course @Override @Transient public String getRemoveMTMQuery() { return "delete from students2courses where course_id = " + id + ";"; } Now it works but I think it's a bad code. Is there a best way to solve this problem?

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