I would like to know if the following is possible in JDO.
I have a 1-N relationship between a Parent and a Child class. So my classes look like
#PersistenceCapable
public class Parent {
#Persistent
private String name;
#Elements(mappedBy = "parent", dependent = "true")
private List<Children> children;
}
#PersistenceCapable
public class Child {
#Persistent
private String name;
#Persistent
private Parent parent;
}
Cascading deletes work fine. I can delete a parent and all its children will be removed from the data store.
If I query the data store for a particular child and have that query delete it, then the child is removed from the table of Child objects but its Parent's list of children will contain a null entry.
I guess this is a fairly dumb question but is there a way to get JDO to update the parent's list on deletion of a child or do I have to do this myself?
Thanks for your replies.
I recommend db4o without the DataNucleus layer. It is just getting in the way of a better performing soluton. We've done testing and found that if you use db4o directly it performs much better and uses less resources.
Related
I am migrating from google datastore api to objectify(i have used datastore at compute engine and migrating to 6.0a1 objectify). In previous version i used this code to query users:
KeyFactory userKeyFactory = datastore.newKeyFactory()
.addAncestors(PathElement.of("UserList", "default"))
.setKind(USER_KIND);
//...save entity
Query<Entity> query = Query.newEntityQueryBuilder()
.setKind(USER_KIND)
.setFilter(PropertyFilter.hasAncestor(datastore.newKeyFactory().setKind("UserList").newKey("default")))
.build();
QueryResults<Entity> queryResults = datastore.run(query);
List<User> result = new ArrayList<>();
queryResults.forEachRemaining(entity -> result.add(transformUser(entity)));
return result;
Now i am trying to make same query with ancestor. However objectify don't work with PathElement. So following code:
ofy().load().type(User.class).ancestor(PathElement.of("UserList", "default")).list()
fails with
java.lang.IllegalArgumentException: No class 'com.google.cloud.datastore.PathElement' was registered
at com.googlecode.objectify.impl.Registrar.getMetadataSafe(Registrar.java:115)
at com.googlecode.objectify.impl.Keys.getMetadataSafe(Keys.java:56)
at com.googlecode.objectify.impl.Keys.getMetadataSafe(Keys.java:65)
at com.googlecode.objectify.impl.Keys.rawKeyOf(Keys.java:47)
at com.googlecode.objectify.impl.Keys.anythingToRawKey(Keys.java:117)
at com.googlecode.objectify.impl.QueryImpl.setAncestor(QueryImpl.java:203)
at com.googlecode.objectify.impl.SimpleQueryImpl.ancestor(SimpleQueryImpl.java:69)
at com.googlecode.objectify.impl.LoadTypeImpl.ancestor(LoadTypeImpl.java:23)
What is proper way to use PathElement with objectify? I see i can create com.googlecode.objectify.Key and pass it as ancestor but it require class, but i don't have UserList class (it is small application, all entities related to single group).
I tried to use this code:
ofy().load().type(User.class).ancestor(datastore.newKeyFactory().setKind("UserList").newKey("default")).list()
Now it fails that User don't have field with #Parent annotation. Here is stacktrace:
com.googlecode.objectify.LoadException: Error loading Key{projectId=projectId, namespace=, path=[PathElement{kind=UserList, id=null, name=default}, PathElement{kind=User, id=1, name=null}]}: Loaded Entity has parent but com.package.model.User has no #Parent
at com.googlecode.objectify.impl.EntityMetadata.load(EntityMetadata.java:84)
at com.googlecode.objectify.impl.LoadEngine.load(LoadEngine.java:187)
at com.googlecode.objectify.impl.LoadEngine$1.nowUncached(LoadEngine.java:145)
at com.googlecode.objectify.impl.LoadEngine$1.nowUncached(LoadEngine.java:131)
at com.googlecode.objectify.util.ResultCache.now(ResultCache.java:30)
at com.googlecode.objectify.impl.Round$1.nowUncached(Round.java:66)
at com.googlecode.objectify.util.ResultCache.now(ResultCache.java:30)
at com.googlecode.objectify.impl.HybridQueryResults.lambda$load$1(HybridQueryResults.java:87)
at com.google.common.collect.Iterators$5.transform(Iterators.java:757)
at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:48)
at com.google.common.collect.MultitransformedIterator.next(MultitransformedIterator.java:66)
at com.google.common.collect.Iterators$4.computeNext(Iterators.java:623)
at com.google.common.collect.AbstractIterator.tryToComputeNext(AbstractIterator.java:145)
at com.google.common.collect.AbstractIterator.hasNext(AbstractIterator.java:140)
at com.googlecode.objectify.impl.HybridQueryResults.hasNext(HybridQueryResults.java:92)
at com.googlecode.objectify.util.IteratorFirstResult.nowUncached(IteratorFirstResult.java:31)
at com.googlecode.objectify.util.ResultCache.now(ResultCache.java:30)
at com.googlecode.objectify.LoadResult.now(LoadResult.java:25)
at com.package.UserObjectifyRepository.getUserByEmail(UserObjectifyRepository.java:43)
...
Caused by: java.lang.IllegalStateException: Loaded Entity has parent but com.package.model.User has no #Parent
at com.googlecode.objectify.impl.KeyMetadata.setKey(KeyMetadata.java:142)
at com.googlecode.objectify.impl.KeyMetadata.setKey(KeyMetadata.java:122)
at com.googlecode.objectify.impl.KeyPopulator.load(KeyPopulator.java:24)
at com.googlecode.objectify.impl.translate.ClassPopulator.load(ClassPopulator.java:118)
at com.googlecode.objectify.impl.translate.ClassTranslator.loadSafe(ClassTranslator.java:109)
at com.googlecode.objectify.impl.translate.NullSafeTranslator.load(NullSafeTranslator.java:21)
at com.googlecode.objectify.impl.EntityMetadata.load(EntityMetadata.java:80)
.. 125 more
I suppose correct way to fix this is to have parent field in my User entity, something like this:
#Parent
private UserList userList;
But i haven't such entity "UserList", i need ancestor just to make query with strong consistency.
UPD: Error is gone if i adding this code:
import com.google.cloud.datastore.Key;
#Parent
private Key userList;
Is it proper way to make consistent query?
The #Parent annotation requires a key.
You just have to create a key, so it can understand that Parent/Child relationship.
Given that, in Objectify, an entity group is not defined by a class, but by an instance, and that you can create child entites with a parent Key that points to a nonexistant entity, how would you do that? (I'm looking for a simple example. The statements above are from Objectify documentation, and I'm confused.)
Just create a Key with an arbitrary id. A simple example:
class Foo {
#Parent Key<Par> parent;
#Id Long id;
// ...constructors, etc
}
// Create a parent key for which an entity may or may not exist, doesn't matter
Key<Par> parent = Key.create(Par.class, 123L);
Foo foo = new Foo(parent, someId);
ofy().save().entity(foo).now();
I'm writing a JFace dialog, and I'd like to use databing to a model object.
Looking at code I can see that there are times when I find a PojoProperties used to build the binding, while other time it is used a PojoObservables.
Looking at the Javadoc I can read:
PojoObservables: A factory for creating observable objects for POJOs (plain old java objects) that conform to idea of an object with getters and setters but does not provide property change events on change.
PojoProperties: A factory for creating properties for POJOs (plain old Java objects) that conform to idea of an object with getters and setters but does not provide property change events on change.
The same question applies to the difference that exists between BeansObservables and BeansProperties
The (obvious) difference sems to be that the observable allows to observe objects and the properties allows to observe properties, but since a Pojo has a getter and a setter for its data, what is the difference between them? And which of them should I choose for my dialog?
Here follows a code excerpt:
The POJO:
public class DataObject {
private String m_value;
public String getValue() {
return m_value;
}
public void setValue(String i_value) {
m_value = i_value;
}
}
The DIALOG (relevant part):
#Override
protected Control createDialogArea(Composite parent) {
Composite container = (Composite) super.createDialogArea(parent);
m_combo = new Combo(container, SWT.BORDER);
m_comboViewer = new ComboViewer(container, SWT.NONE);
}
The BINDING (relevant part):
// using PojoObservable
IObservableValue observeValue = PojoObservables.observeValue(m_dataObject, "value");
IObservableValue observeWidget = SWTObservables.observeSelection(m_combo);
// using PojoProperties
IObservableValue observeValue = PojoProperties.value("value").observe(m_dataObject);
IObservableValue observeWidget = ViewerProperties.singleSelection().observe(m_comboViewer);
I understand that one time I'm using a combo and another I'm using a ComboViewer, but I can get the combo from the viewer and bind the other way if I need...
Also, can I mix the two, for example use the observeValue with the ViewerProperties?
IObservableValue observeValue = PojoObservables.observeValue(m_dataObject, "value");
IObservableValue observeWidget = ViewerProperties.singleSelection().observe(m_comboViewer);
I am playing around a little with JFace viewers (especially ComboViewer) & databinding and discovered that if I use
SWTObservables.observeSelection(comboViewer.getCombo());
then databinding is not working correctly.
However, if I use
ViewersObservables.observeSingleSelection(comboViewer);
Then everything is working as expected.
Maybe this is a special for my case, so to get it a better overview I'll describe my set up in following paragraph.
I have modelObject with field named selectedEntity and entities and bind this ComboViewer to the modelObject.
I want to display all "entities" in model object, if I add any entity to the modelObject.entities collection then I want to this entity be added to combo automatically.
If user selects some item in combo I want to modelObject.selectedEntity be set automatically.
If I set modelObject.selectedEntity I want to combo selection be set automatically.
Source code can be found at: https://gist.github.com/3938502
Since Eclipse Mars, PojoObservables is deprecated in favor of PojoProperties and BeansObservables is deprecated in favor of BeanProperties so the answer to which one should be used has now become evident.
I need to bind request parameters to an instance of the following Java class (getters and setters omitted):
public class ShippingHouse {
private String name;
private String description;
private List<ShippingRule> shippingRules = new ArrayList<ShippingRule>();
}
public class ShippingRule {
private ShippingHouse shippingHouse;
private String name
}
Notice that there is a 1:N relationship between ShippingHouse and ShippingRule, but each ShippingRule also has a reference to the ShippingHouse thaat owns it.
If these were Grails command/domain classes, I would bind them with request parameters
name=foo&description=bar&shippingRules[0].name=sr0&shippingRules[1].name=sr1
But it doesn't seem like this will set the reference to the owning ShippingHouse within each ShippingRule. Is there a way I can bind this automatically, or must I write the code myself?
Don,
You will need to write code to do it yourself using BindUsing or some other approach. The binder doesn't (and shouldn't) assume anything about back references from a parent to a child. If these were GORM entities and the relationship was explicit, that is different, but in your case the binder should not assume that shippingHouse property in the ShippingRule class has anything to do with the shippingRules property in the ShippingHouse class.
Also note that lucke84 said that your "private" is implicit. Make sure you understand what that means if you are going to remove them. If you remove them the compiler is going to generate public getter and setter methods for those properties, which may or may not be what you want.
If you want to implement a 1:N relationship between the two classes, you should use the right grails approach. Something like this:
class ShippingHouse {
String name
String description
static hasMany = [shippingRules: ShippingRule]
}
class ShippingRule {
String name
static belongsTo = [shippingHouse: ShippingHouse]
}
Please note that semicolons are useless and the "private" declaration on class fields is implicit.
I am using POCO classes on an EF4 CTP5 project and I am having trouble deleting child properties. Here's my example (hopefully not too long).
Relevant Portions of the Tour Class
public partial class Tour
{
public Guid TourId { get; private set; }
protected virtual List<Agent> _agents { get; set; }
public void AddAgent(Agent agent)
{
_agents.Add(agent);
}
public void RemoveAgent(Guid agentId)
{
var a = Agents.Single(x => x.AgentId == agentId);
_agents.Remove(Agents.Single(x => x.AgentId == agentId));
}
}
Command Handler
public class DeleteAgentCommandHandler : ICommandHandler<DeleteAgentCommand>
{
private readonly IRepository<Core.Domain.Tour> _repository;
private readonly IUnitOfWork _unitOfWork;
public DeleteAgentCommandHandler(
IRepository<Core.Domain.Tour> repository,
IUnitOfWork unitOfWork
)
{
_repository = repository;
_unitOfWork = unitOfWork;
}
public void Receive(DeleteAgentCommand command)
{
var tour = _repository.GetById(command.TourId);
tour.RemoveAgent(command.AgentId);
// The following line just ends up calling
// DbContext.SaveChanges(); on the current context.
_unitOfWork.Commit();
}
}
Here's the error that I get when my UnitOfWork calls DbContext.SaveChanges()
The operation failed: The relationship could not be changed because one or more of the foreign-key properties is non-nullable. When a change is made to a relationship, the related foreign-key property is set to a null value. If the foreign-key does not support null values, a new relationship must be defined, the foreign-key property must be assigned another non-null value, or the unrelated object must be deleted.
This is happening because EF wont just automatically delete the an Agent entity from the database just because it has been removed from the Agents collection in my Tour class.
I need to explicitly call dbContext.Agents.DeleteObject(a);, but my problem is, I don't have access to the dbContext from within my POCO.
Is there any way to handle this scenario?
With your current architecture I am afraid you need to feed your DeleteAgentCommandHandler with a second repository (IRepository<Core.Domain.Agent>, I guess) and then call something like Delete(command.AgentId) on that second repository.
Or you could extend your IUnitOfWork to be a factory of repositories, so the interface would get an additional method like T CreateRepository<T>() which allows you to pull any instance of your generic repository from the unit of work. (Then you only need to inject IUnitOfWork into the DeleteAgentCommandHandler, and not the repositories anymore.)
Or stay away from generic repositories in your business/UI layer. If Agent is completely dependent on Tour it doesn't need to have a repository at all. A non-generic ITourRepository could have methods to handle the case of removing an agent from a tour in the database layer appropriately.
This does seem like something that should work. I've found this post which suggests this feature is being investigated for future versions:
http://social.msdn.microsoft.com/Forums/en-US/adonetefx/thread/58a31f34-9d2c-498d-aff3-fc96988a3ddc/
I've also found another post (somewhere - unfortunately I lost it) which suggested adding the parent entity's key to the child entity in your DbContext OnModelCreating method like this:
modelBuilder.Entity<Agent>()
.HasKey(AgentId)
.HasKey(TourId);
Currently this throws an exception at runtime using code-first, although I have got this working when using an EDMX file by hacking the XAML to include the parent key in the store data model as well as the conceptual data model. I think this difference in behaviour is because in the case of the EDMX file, EF trusts that the store metadata it holds is accurate, whereas code-first checks the database to see whether it's model matches.
Another way which may work although I haven't yet tried it yet, is to include the parent key as a compound key in the child table so that code-first is happy. Obviously changing the database or hacking the XAML are both less than ideal and workarounds at best.