I have a JPA entity already persisted in the database.   
I would like to have a copy of it (with a different id), with some fields modified.

What is the easiest way to do this? Like:

 * setting it&#39;s `@Id` field to `null` and persisting it will work?
 * will I have to create a clone method for the entity (copying all fields except the `@Id`)?
 * is there any other approach (like using a cloning framework)?


How to clone a JPA entity

What&#39;s the difference between entity and class?

I have a JPA-persisted object model that contains a many-to-one relationship: an `Account` has many `Transactions`. A `Transaction` has one `Account`.

Here&#39;s a snippet of the code:

    @Entity
    public class Transaction {
        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private Long id;
    
        @ManyToOne(cascade = {CascadeType.ALL},fetch= FetchType.EAGER)
        private Account fromAccount;
    ....

    @Entity
    public class Account {
        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private Long id;
        @OneToMany(cascade = {CascadeType.ALL},fetch= FetchType.EAGER, mappedBy = &quot;fromAccount&quot;)
        private Set&lt;Transaction&gt; transactions;


I am able to create an `Account` object, add transactions to it, and persist the `Account` object correctly. But, when I create a transaction, *using an existing already persisted Account*,  and persisting the *the Transaction*, I get an exception:

&gt;Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: com.paulsanwald.Account
    	at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:141) 

So, I am able to persist an `Account` that contains transactions, but not a Transaction that has an `Account`. I thought this was because the `Account` might not be attached, but this code still gives me the same exception:

    if (account.getId()!=null) {
        account = entityManager.merge(account);
    }
    Transaction transaction = new Transaction(account,&quot;other stuff&quot;);
     // the below fails with a &quot;detached entity&quot; message. why?
    entityManager.persist(transaction);

How can I correctly save a `Transaction`, associated with an already persisted `Account` object?

PersistentObjectException: detached entity passed to persist thrown by JPA and Hibernate

We are having some trouble designing our multi-threaded Entity Framework driven application and would like some guidance. We are creating entities on different threads, the entities are added to collections which are then data-bound to various WPF controls. The ObjectContext class is not thread-safe, so managing this we have essentially have 2 solutions:

Solution 1 has a single context and carefully use locking to ensure no 2 threads access it at the same time. This would be relatively simple to implement but would require the context to be alive for the duration of the application. Is it a bad idea to have a single context instance open like this?

Solution 2 is to create context objects on-demand and then detach the objects immediately, then hold them in our own collections, then re-attach them to do any updating. This has some serious problems for use though, as when the objects are detached they lose references to the navigation property objects. Also there is the problem that 2 threads could still try to access a single object, and both try to attach() it to a context. Also, we would need to supply a new context every time we wanted to access entities&#39; navigation properties.

Q: Are either of the two solutions valid, if not how do you recommend we tackle this?

Entity Framework and Multi threading

I have two tables: `Ta` and `Tb`. They have exactly the same table structure but different table names.


I try to create one entity class to map the table structures.  Some of my common application modules will use this entity class to dynamically query and update either `Ta` or `Tb` based on parameters.  Can it be done in JPA?  How can I write the program to dynamically mapping the entity class to different tables at run time?
   

 

JPA, How to use the same class (entity) to map different tables?

I want to use JPA (eclipselink) to get data from my database. The database is changed by a number of other sources and I therefore want to go back to the database for every find I execute. I have read a number of posts on disabling the cache but this does not seem to be working. Any ideas?

I am trying to execute the following code:
 

            EntityManagerFactory entityManagerFactory =  Persistence.createEntityManagerFactory(&quot;default&quot;);
            EntityManager em = entityManagerFactory.createEntityManager();
            
            MyLocation one = em.createNamedQuery(&quot;MyLocation.findMyLoc&quot;).getResultList().get(0);
    
            MyLocation two = em.createNamedQuery(&quot;MyLocation.findMyLoc&quot;).getResultList().get(0);    
    
            System.out.println(one==two);

one==two is true while I want it to be false.

I have tried adding each/all the following to my persistence.xml

    &lt;property name=&quot;eclipselink.cache.shared.default&quot; value=&quot;false&quot;/&gt;
    &lt;property name=&quot;eclipselink.cache.size.default&quot; value=&quot;0&quot;/&gt;
    &lt;property name=&quot;eclipselink.cache.type.default&quot; value=&quot;None&quot;/&gt;

I have also tried adding the @Cache annotation to the Entity itself:

    @Cache(
      type=CacheType.NONE, // Cache nothing
      expiry=0,
      alwaysRefresh=true
    )

Am I misunderstanding something?


Disable caching in JPA (eclipselink)

Here&#39;s the table

**Users**

    UserId
    UserName
    Password
    EmailAddress

and the code..

&lt;!-- language: lang-csharp --&gt;

    public void ChangePassword(int userId, string password){
    //code to update the password..
    }


How to update only one field using Entity Framework?

I receive following error when I save the object using Hibernate 

    object references an unsaved transient instance - save the transient instance before flushing

 

How to fix the Hibernate &quot;object references an unsaved transient instance - save the transient instance before flushing&quot; error

How do I set a default value in Hibernate field?

How to set a default entity property value with Hibernate

It seems to me that I have to retrieve an object before I delete it with entity framework like below

    var customer = context.Customers.First(c =&gt; c.Id == 1);
    
    context.DeleteObject(customer);
    
    context.Savechanges();

So I need to hit database twice. Is there a easier way?



How to delete an object by id with entity framework

What is the difference between persist() and merge() in Hibernate?

`persist()` can create a UPDATE &amp; INSERT query, eg:

    SessionFactory sef = cfg.buildSessionFactory();
    Session session = sef.openSession();
    A a=new A();
    session.persist(a);
    a.setName(&quot;Mario&quot;);
    session.flush();

in this case **query** will be generated like this:

    Hibernate: insert into A (NAME, ID) values (?, ?)
    Hibernate: update A set NAME=? where ID=?

so `persist()` method can **generate** an Insert and an Update.

Now with `merge()`:

    SessionFactory sef = cfg.buildSessionFactory();
    Session session = sef.openSession();
    Singer singer = new Singer();
    singer.setName(&quot;Luciano Pavarotti&quot;);
    session.merge(singer);
    session.flush();

This is what I see in the database:

    SINGER_ID	SINGER_NAME
    1	        Ricky Martin
    2	        Madonna
    3	        Elvis Presley
    4	        Luciano Pavarotti

Now update a record using `merge()`
        
    SessionFactory sef = cfg.buildSessionFactory();
    Session session = sef.openSession();
    Singer singer = new Singer();
    singer.setId(2);
    singer.setName(&quot;Luciano Pavarotti&quot;);
    session.merge(singer);
    session.flush();

This is what I see in the database:

    SINGER_ID	SINGER_NAME
    1	        Ricky Martin
    2	        Luciano Pavarotti
    3	        Elvis Presley


What is the difference between persist() and merge() in JPA and Hibernate?

I want to insert 20000 records in a table by entity framework and it takes about 2 min. Is there any way other than using SP to improve its performance. This is my code: 

     foreach (Employees item in sequence)
     {
       t = new Employees ();
       t.Text = item.Text;
       dataContext.Employees.AddObject(t);                  
     }
     dataContext.SaveChanges();

Improving bulk insert performance in Entity framework

I am confused to understand what is the meaning of this words:

`Entity`, `Model`, `DataModel`, `ViewModel`

Can any body help me to understanding them please? Thank you all.

what is difference between a Model and an Entity

I tried to gather some information about the following way to delete automatically child entity when a parent entity is deleted. Seems that the most common way is to use one those three annotation: `cascade={&quot;remove&quot;}` OR `orphanRemoval=true` OR `ondelete=&quot;CASCADE&quot;`. 

 I am a bit confused about the third one: `ondelete=&quot;CASCADE&quot;`, as the explanation in doctrine official documentation about this one are very scarce) and I would love if someone could **confirm me the following information** I gathered and understand from my research on the net and experience...   

What does it do?

`cascade={&quot;remove&quot;}`
==&gt; the entity on the inverse side is deleted when the owning side entity is. Even if you are in a `ManyToMany` with other owning side entity.   
- should be used on collection (so in `OneToMany` or `ManyToMany` relationship)  
- implementation in the ORM

`orphanRemoval=true`
==&gt; the entity on the inverse side is deleted when the owning side entity is AND it is not connected to any other owning side entity anymore. (ref.  [doctrine official_doc](http://doctrine-orm.readthedocs.org/en/latest/reference/xml-mapping.html?highlight=orphanremoval#defining-many-to-one-associations)
- implementation in the ORM   
- can be used with `OneToOne`, `OneToMany` or `ManyToMany`

`onDelete=&quot;CASCADE&quot;` 
==&gt; this will add On Delete Cascade to the foreign key column in the database  
- This strategy is a bit tricky to get right but can be very powerful and fast. (ref.  [doctrine official_doc](http://doctrine-orm.readthedocs.org/en/latest/reference/working-with-objects.html?highlight=tricky#removing-entities) ... but haven&#39;t read more explanations)   
- ORM has to do less work (compared to the two previous ways of doing it) and therefore should have better performance.

**other information**   
- all those 3 ways of doing are implemented on bidirectional relationship entities (**_right???_**)    
- using `cascade={&quot;remove&quot;}` completely by-passes any foreign key onDelete=CASCADE. (ref. [doctrine_official_doc](http://doctrine-orm.readthedocs.org/en/latest/reference/working-with-objects.html?highlight=tricky#removing-entities))


EXAMPLE ON HOW TO USE IT IN CODE
--
- `orphanRemoval` and `cascade={&quot;remove&quot;}` are defined in the inversed entity class.  
- `ondelete=&quot;CASCADE&quot;` is defined in the owner entity
- you can also just write `@ORM\JoinColumn(onDelete=&quot;CASCADE&quot;)` and let doctrine handle the column names

**cascade={&quot;remove&quot;}**

    /**
    * @OneToMany(targetEntity=&quot;Phonenumber&quot;, mappedBy=&quot;contact&quot;, cascade={&quot;remove&quot;})
    */
    protected $Phonenumbers

 
**orphanRemoval=true**

    /**
    * @OneToMany(targetEntity=&quot;Phonenumber&quot;, mappedBy=&quot;contact&quot;, orphanRemoval=true)
    */
    protected $Phonenumbers

**onDelete=&quot;CASCADE&quot;**

    /** 
    * @ManyToOne(targetEntity=&quot;Contact&quot;, inversedBy=&quot;phonenumbers&quot;)
    * @JoinColumn(name=&quot;contact_id&quot;, referencedColumnName=&quot;contact_id&quot;, onDelete=&quot;CASCADE&quot;)
    */ 
    protected $contact; 



cascade={&quot;remove&quot;} VS orphanRemoval=true VS ondelete=&quot;CASCADE

I am trying to replicate an example found on MSDN. I am using ASP.NET and EF 4.1 (CTP?). I&#39;ve used NuGet to install the EntityFramework package.

I am getting this error: `The provider did not return a ProviderManifestToken string` ...
and the database is never created.

Here is my connection string:

    &lt;add name=&quot;HospitalContext&quot;
       connectionString=
       &quot;data source=.\SQLExpress;initial catalog=NewTestDB;integrated security=True;&quot;
       providerName=&quot;System.Data.SqlClient&quot;/&gt;

Here is my code:

    var pat = new Patient { Name = &quot;Shane123132524356436435234&quot; };
    db.Patients.Add(pat);

    var labResult = new LabResult { Result = &quot;bad&quot;, Patient = pat };
          
    int recordAffected = db.SaveChanges();

Here is my context:

    public class HospitalContext : DbContext
    {
        static HospitalContext()
        {
            Database.SetInitializer(new HostpitalContextInitializer());
        }

        public DbSet&lt;Patient&gt; Patients { get; set; }
        public DbSet&lt;LabResult&gt; LabResults { get; set; }
    }

    public class HostpitalContextInitializer :
                 DropCreateDatabaseIfModelChanges&lt;HospitalContext&gt;
    {
        protected override void Seed(HospitalContext context)
        {
            context.Patients.Add(new Patient { Name = &quot;Fred Peters&quot; });
            context.Patients.Add(new Patient { Name = &quot;John Smith&quot; });
            context.Patients.Add(new Patient { Name = &quot;Karen Fredricks&quot; });
        }
    }

This is a fully patched SQL 2008 system, with VS 2010 SP1.


EF 4.1 exception &quot;The provider did not return a ProviderManifestToken string&quot;

Is there a way to decorate your POCO classes to automatically eager-load child entities without having to use `Include()` every time you load them? 

Say I have a Class Car, with Complex-typed Properties for Wheels, Doors, Engine, Bumper, Windows, Exhaust, etc. And in my app I need to load my car from my DbContext 20 different places with different queries, etc. I don&#39;t want to have to specify that I want to include all of the properties every time I want to load my car. 

I want to say 

    List&lt;Car&gt; cars = db.Car
                    .Where(x =&gt; c.Make == &quot;Ford&quot;).ToList();
    
    //NOT .Include(x =&gt; x.Wheels).Include(x =&gt; x.Doors).Include(x =&gt; x.Engine).Include(x =&gt; x.Bumper).Include(x =&gt; x.Windows)
    
    
    foreach(Car car in cars)
    {
    
    //I don&#39;t want a null reference here.
    
    String myString = car.**Bumper**.Title;
    }

Can I somehow decorate my POCO class or in my `OnModelCreating()` or set a configuration in EF that will tell it to just load all the parts of my car when I load my car? I want to do this eagerly, so my understanding is that making my navigation properties virtual is out. I know NHibernate supports similar functionality. 

Just wondering if I&#39;m missing something. Thanks in advance!

Cheers,

Nathan


I like the solution below, but **am wondering if I can nest the calls to the extension methods.** For example, say I have a similar situation with Engine where it has many parts I don&#39;t want to include everywhere. Can I do something like this? (I&#39;ve not found a way for this to work yet). This way if later I find out that Engine needs FuelInjectors, I can add it only in the BuildEngine and not have to also add it in BuildCar. **Also if I can nest the calls, how can I nest a call to a collection? Like to call BuildWheel() for each of my wheels from within my BuildCar()?**

    public static IQueryable&lt;Car&gt; BuildCar(this IQueryable&lt;Car&gt; query) {
         return query.Include(x =&gt; x.Wheels).BuildWheel()
                     .Include(x =&gt; x.Doors)
                     .Include(x =&gt; x.Engine).BuildEngine()
                     .Include(x =&gt; x.Bumper)
                     .Include(x =&gt; x.Windows);
    }
    
    public static IQueryable&lt;Engine&gt; BuildEngine(this IQueryable&lt;Engine&gt; query) {
         return query.Include(x =&gt; x.Pistons)
                     .Include(x =&gt; x.Cylendars);
    }

    //Or to handle a collection e.g.
     public static IQueryable&lt;Wheel&gt; BuildWheel(this IQueryable&lt;Wheel&gt; query) {
         return query.Include(x =&gt; x.Rim)
                     .Include(x =&gt; x.Tire);
    }


Here is another very similar thread in case it is helpful to anyone else in this situation, but it still doesn&#39;t handle being able to make nexted calls to the extension methods.

https://stackoverflow.com/questions/3356541/entity-framework-linq-query-include-multiple-children-entities


Entity Framework - Is there a way to automatically eager-load child entities without Include()?

I&#39;m trying to ignore the &quot;Automatic&quot; migration using Entity Framework 6.0 rc1. My problem is that I don&#39;t want this feature right now and every time that my application runs I can see all entity logs trying to create all tables.


Anticipate thanks.

How can I disable migration in Entity Framework 6.0

What is the difference between a DTO and an Entity? In details these are my questions:

 1. What fields should the DTOs have? For example my entity classes are:


        @Entity
        public class MyFirstEntity implements Serializable {

            @Id @GeneratedValue
            private Long id;

            private String stringData;

            @OneToOne
            private MySecondEntity mySecondEntity;

            @OneToMany
            private List&lt;MySecondEntity&gt; mySecondEntitesList;

        }

        @Entity
        public class MySecondEntity implements Serializable {

            @Id @GeneratedValue
            private Long id;

            private Integer integerData;

            @ManyToOne
            private MyFirstEntity myFirstEntity;

        }

There is a one-sided connection (One-to-one) and a two-sided connection (Many-to-one), a simple String and Integer data and of course the ids. What to put from them in the `MyFirstDTO` and `MySecondDTO` classes? 

  2. If there is an inheritance between the entities, then how should I represent it in the DTOs? For example:

        @Entity
        public class MyFirstEntity extends MySecondEntity {
            ....
        }

        @Entity
        public class MyFirstDTO extends MySecondDTO {
            ....
        }

  3. How should I use them? For example, I find out this: I&#39;m working on a web project. The user of the webpage wants to register. He/She fills the forms, and sends it to the server. On the server side I create first a DTO, because its fields have the validations. From the DTO I create an Entity and persist it to the database. When there is a request for an entity, I convert the requested entity to DTO, and give it to the user on the client side. Is it a good imagination, or not?

Difference between Entity and DTO

Symfony2 collection of Entities - how to add/remove association with existing entities?

I want to check if entity is in a Collection member (`@OneToMany` or `@ManyToMany`) of another entity:

    if (entity2.getEntities1().contains(entity1)) { }



Should I write equals() and hashCode() methods in JPA entities?

Can someone explain these 3 concepts and the differences between them with respect to an MVC framework along with an example. To me these appear almost equivalent, and it seems they are used interchangeably in some articles and not in others. 

Differentiating between domain, model, and entity with respect to MVC

I&#39;m seriously confused about the concept of the &#39;Model&#39; in MVC.  Most frameworks that exist today put the Model between the Controller and the database, and the Model almost acts like a database abstraction layer.  The concept of &#39;Fat Model Skinny Controller&#39; is lost as the Controller starts doing more and more logic.

In DDD, there is also the concept of a Domain Entity, which has a unique identity to it.  As I understand it, a user is a good example of an Entity (unique userid, for instance).  The Entity has a life-cycle -- it&#39;s values can change throughout the course of the action -- and then it&#39;s saved or discarded.

The Entity I describe above is what I thought Model was supposed to be in MVC?  How off-base am I?

To clutter things more, you throw in other patterns, such as the Repository pattern (maybe putting a Service in there).  It&#39;s pretty clear how the Repository would interact with an Entity -- how does it with a Model?

Controllers can have multiple Models, which makes it seem like a Model is less a &quot;database table&quot; than it is a unique Entity.

**UPDATE:** [In this post][1] the Model is described as something with knowledge, and it can be singular or a collection of objects.  So it&#39;s sound more like an Entity and a Model are more or less the same.  The Model is an all encompassing term, where an Entity is more specific.  A Value Object would be a Model as well.  At least in terms of MVC.  Maybe???

So, in very rough terms, which is better?

No &quot;Model&quot; really ...

    class MyController {
        public function index() {
            $repo = new PostRepository();
            $posts = $repo-&gt;findAllByDateRange(&#39;within 30 days&#39;);
            foreach($posts as $post) {
                echo $post-&gt;Author;
            }
        }
    }

Or this, which has a Model as the DAO?

    class MyController {
        public function index() {
            $model = new PostModel();
            // maybe this returns a PostRepository?
            $posts = $model-&gt;findAllByDateRange(&#39;within 30 days&#39;);
            while($posts-&gt;getNext()) {
                echo $posts-&gt;Post-&gt;Author;
            }
        }
    }

Both those examples didn&#39;t even do what I was describing above.  I&#39;m clearly lost.  Any input?


  [1]: http://www.codinghorror.com/blog/2008/05/understanding-model-view-controller.html

DDD and MVC: Difference between &#39;Model&#39; and &#39;Entity&#39;

The database is created successfully (as are the tables) but is not seeded. I have spent several hours and read tons of articles but have not been able to get it. Any suggestions?

On a side note, is it possible to call the initializer without having a reference to my DatabaseContext in the client?

I have included all the relevant code I could think of. If anything else would be helpful, please let me know.

Things I&#39;ve Tried:

1. I deleted my connection string (since it defaults to sqlexpress anyways, just the name changed)
2. I changed DropCreateDatabaseIfModelChanges to DropCreateDatabaseAlways, still the same.

Edit: The really weird thing is it worked once, but I have no idea how or why it broke again. I am assuming connection strings, but who knows.

DatabaseInitializer.cs

    public class DatabaseInitializer : DropCreateDatabaseIfModelChanges&lt;DatabaseContext&gt;
    {
      protected override void Seed(DatabaseContext context)
      {
        // Seeding data here
        context.SaveChanges();
      }
    }

DatabaseContext.cs

    public class DatabaseContext : DbContext
    {
      protected override void OnModelCreating(DbModelBuilder mb)
      {
        // Random mapping code
      }

      public DbSet&lt;Entity1&gt; Entities1 { get; set; }
      public DbSet&lt;Entity2&gt; Entities2 { get; set; }

    }
    
Global.asax.cs - Application_Start()

    protected void Application_Start()
    {
      Database.SetInitializer&lt;DatabaseContext&gt;(new DatabaseInitializer());
      AreaRegistration.RegisterAllAreas();
      RegisterGlobalFilters(GlobalFilters.Filters);
      RegisterRoutes(RouteTable.Routes);
    }

Client web.config

    &lt;connectionStrings&gt;
      &lt;add name=&quot;DatabaseContext&quot; connectionString=&quot;data source=.\SQLEXPRESS;Database=Database;Integrated Security=SSPI;&quot; providerName=&quot;System.Data.SqlClient&quot; /&gt;
    &lt;/connectionStrings&gt;

#SOLUTION#

For the sake of documentation, I am sharing my solution here. Navigating all the comments would be a pain anyways. In the end I had DatabaseInitializer and DatabaseContext in separate classes. I don&#39;t really understand while these tiny changes fixed it, but here it is.

DatabaseInitializer.cs

    public class DatabaseInitializer : CreateDatabaseIfNotExists&lt;DatabaseContext&gt;
    {
      protected override void Seed(DatabaseContext context)
      {
        // Seed code here
      }
    }

DatabaseContext.cs

    public class DatabaseContext : DbContext
    {
      public DatabaseContext() : base(&quot;MyDatabase&quot;) { }

      protected override void OnModelCreating(DbModelBuilder mb)
      {
        // Code here
      }
      
      public DbSet&lt;Entity&gt; Entities { get; set; }
      // Other DbSets
    }

Global.asax.cs - Application_Start()

    protected void Application_Start()
    {
      Database.SetInitializer(new DatabaseInitializer());
      AreaRegistration.RegisterAllAreas();
      RegisterGlobalFilters(GlobalFilters.Filters);
      RegisterRoutes(RouteTable.Routes);
    }

    

All Entity Solutions on Gang of Coders

Total of 23 Entity Solutions