I'm having some trouble using nHibernate, automapping and a class structure using multiple chains of abstract classes
It's something akin to this
public abstract class AbstractClassA {}
public abstract class AbstractClassB : AbstractClassA {}
public class ClassA : AbstractClassB {}
When I attempt to build these mappings, I receive the following error
"FluentNHibernate.Cfg.FluentConfigurationException was unhandled
Message: An invalid or incomplete configuration was used while creating a SessionFactory. Check PotentialReasons collection, and InnerException for more detail.
Database was not configured through Database method."
However, if I remove the abstract keyword from AbstractClassB, everything works fine. The problem only occurs when I have more than one abstract class in the class hierarchy.
I've manually configured the automapping to include both AbstractClassA and AbstractClassB using the following binding class
public class BindItemBases : IManualBinding
{
public void Bind(FluentNHibernate.Automapping.AutoPersistenceModel model)
{
model.IncludeBase<AbstractClassA>();
model.IncludeBase<AbstractClassB>();
}
}
I've had to do a bit of hackery to get around this, but there must be a better way to get this working. Surely nHibernate supports something like this, I just haven't figured out how to configure it right.
Cheers,
James
Why do you include abstract classes in your AutoMappings, are they presented in the database too? Could you provide the inner exception Fluent throws?
model.IncludeBase<AbstractClassA>();
model.IncludeBase<AbstractClassB>();
With this in place you are trying to map AbstractClassB to the database, which is supposedly not what you want.
Related
So, I created a DataContext (Linq-Sql) in VS from an existing database. It has a table called Users, thus I have a User object. In particular, I want to focus on the UserID and Username properties.
Now, I have an interface:
interface IUser
{
int Id { get; }
string Username { get; }
}
I want to create a partial User class and implement IUser. The reason for this is so that I can treat any User as an IUser in many places and not be concerned about the precise User class:
public partial class User : IUser
{
public int Id
{
get { return UserID; }
}
}
I don't implement the Username get property because I know that the entity object already implements it.
When I have a query like dc.Users.SingleOrDefault(p => p.Id == 5); I know that it's an error because it'll translate that call to an SQL statement and it's going to try to find the Id column, which doesn't exist - UserID exists. So I understand this mapping issue.
When I query dc.Users.SingleOrDefault(p => p.Username == "admin"), it also throws an error, BUT Username IS indeed an existing column in the database, so my impression is that no custom/additional mapping needs to take place. What am I missing?
Can someone point me to a good source on how to combat Linq vs. partial classes implement a custom interface?
Update Question:
Before I try it, does anyone know if "rigging" the datacontext.designer.cs file with our custom interfaces (to implement to the classes themselves instead of in a separate partial class file) will work? Is there a consequence of doing this?
I've come across this before using Generics and LINQ, and the way I solved it was to change p.Id == 5 to p.Id.Equals(5) and LINQ was able to map the query.
In regards to rigging autogenerated code, I have done this in my projects, the only annoyance is having to type all the interfaces again if you regenerate your DBML file. I looked in to dynamically adding interfaces to classes and found this SO post, but I haven't tried it out yet:
What is the nicest way to dynamically implement an interface in C#?
Either way, re-typing is a much better trade off for us right now as we've been able to remove a lot of duplication in our implementation code with this method.
Unfortunately I'm not experienced enough with LINQ or .NET to explain why Equals() works when == does not :)
I refer to it as the "delivery boy". I've seen several variants of it but the issue is that a class has dependency for the sole purpose of passing it on to collaborators and never using the dependency itself.
(I'm using PHP because it's what I'm most familiar with but this is language agnostic)
class Dependency{}
class B {
public function setDependency(Dependency $dependency) {
//...
}
}
class A {
private $b;
private $dependency;
public function __construct(Dependency $dependency, B $b) {
$this->dependency = $dependency;
$this->b = $b;
}
public function foo() {
$this->b->setDependency($this->dependency);
}
}
Probably the most common variant I see in the wild is abusing inheritance for this purpose, having a property in the parent class which exists so that the child classes have access to the dependency even if the parent class never actually uses the dependency itself.
class Dependency{}
class A {
protected $dependency;
public function __construct(Dependency $dependency) {
$this->dependency = $dependency;
}
}
class B extends A {
public function foo() {
$this->dependency->bar();
}
}
I see this in code far more than I'd like and it doesn't make me very happy! I just wondered if there was a name for this so that I can link people to reading materials on why it's a bad idea. As it stands, I don't know what to search for!
I'm not aware of any name, but I kind of like Delivery boy... though I suppose some might consider the name borderline offensive.
Typically this problem is solved with either Dependency Injection or a Service Locator, although way too many people use Singleton for this (inappropriately).
I'm not familiar enough with PHP to know if PHP offers a real DI solution (as opposed to poor man's DI), but I think a service locator would be acceptable if there isn't (even though service locator is often a code smell in itself).
The problem related to inheritance in the second snippet looks like to me "Broken Hierarchy". This smell occurs when the base class and its derived class do not share an IS-A relationship. It is very common to find code that uses inheritance just for convenience (for reuse) and not because it makes sense to have a hierarchy where the participating classes are are related (by IS-A relationship).
(I borrowed the smell terminology (i.e. Broken Hierarchy) from the book "Refactoring for software design smells")
In my Google Web Toolkit project, I got the following error:
com.google.gwt.user.client.rpc.SerializationException: Type ‘your.class.Type’ was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.
What are the possible causes of this error?
GWT keeps track of a set of types which can be serialized and sent to the client. your.class.Type apparently was not on this list. Lists like this are stored in .gwt.rpc files. These lists are generated, so editing these lists is probably useless. How these lists are generated is a bit unclear, but you can try the following things:
Make sure your.class.Type implements java.io.Serializable
Make sure your.class.Type has a public no-args constructor
Make sure the members of your.class.Type do the same
Check if your program does not contain collections of a non-serializable type, e.g. ArrayList<Object>. If such a collection contains your.class.Type and is serialized, this error will occur.
Make your.class.Type implement IsSerializable. This marker interface was specifically meant for classes that should be sent to the client. This didn't work for me, but my class also implemented Serializable, so maybe both interfaces don't work well together.
Another option is to create a dummy class with your.class.Type as a member, and add a method to your RPC interface that gets and returns the dummy. This forces the GWT compiler to add the dummy class and its members to the serialization whitelist.
I'll also add that if you want to use a nested class, use a static member class.
I.e.,
public class Pojo {
public static class Insider {
}
}
Nonstatic member classes get the SerializationException in GWT 2.4
I had the same issue in a RemoteService like this
public List<X> getX(...);
where X is an interface. The only implementation did conform to the rules, i.e. implements Serializable or IsSerializable, has a default constructor, and all its (non-transient and non-final) fields follow those rules as well.
But I kept getting that SerializationException until I changed the result type from List to X[], so
public X[] getX(...);
worked. Interestingly, the only argument being a List, Y being an interface, was no problem at all...
I have run into this problem, and if you per chance are using JPA or Hibernate, this can be a result of trying to return the query object and not creating a new object and copying your relavant fields into that new object. Check the following out, which I saw in a google group.
#SuppressWarnings("unchecked")
public static List<Article> getForUser(User user)
{
List<Article> articles = null;
PersistenceManager pm = PMF.get().getPersistenceManager();
try
{
Query query = pm.newQuery(Article.class);
query.setFilter("email == emailParam");
query.setOrdering("timeStamp desc");
query.declareParameters("String emailParam");
List<Article> results = (List<Article>) query.execute(user.getEmail
());
articles = new ArrayList<Article>();
for (Article a : results)
{
a.getEmail();
articles.add(a);
}
}
finally
{
pm.close();
}
return articles;
}
this helped me out a lot, hopefully it points others in the right direction.
Looks like this question is very similar to what IsSerializable or not in GWT?, see more links to related documentation there.
When your class has JDO annotations, then this fixed it for me (in addition to the points in bspoel's answer) : https://stackoverflow.com/a/4826778/1099376
I'm fairly new to Ninject, but I have successfully managed to use it for DI using a custom provider.
The binding is initialised as follows
kernel = new StandardKernel();
kernel.Bind<IPatientRecordLocator>().ToProvider<PatientRecordLocatorProvider>();
and in the custom provider I call Activator.CreateInstance like so
protected override IPatientRecordLocator CreateInstance(IContext context)
{
var name = ConfigurationManager.AppSettings["PatientRecordLocator"];
var typeName = name.Split(',')[0];
var assemblyName = name.Split(',')[1];
return Activator.CreateInstance(assemblyName, typeName).Unwrap() as IPatientRecordLocator;
}
(yes, I am aware that there is no error handling, etc. in the code above :) )
and all this works like a charm.
Now, the problem I'm facing is when I introduce a new class that I wish to inject into instances of IPatientRecordLocator. The problem occurs when I add a constructor like the following to e.g. one of these classes
[Inject]
public MockPatientRecordLocator (IContactAdapter contactAdapter)
{
...
}
Then, for Activator.CreateInstance to work I also have to add a parameterless constructor to class MockPatientRecordLocator, i.e.
public MockPatientRecordLocator()
{
}
So, my question is: how can I make Ninject inject an instance of a class that implements IContactAdapter into e.g. MockPatientRecordLocator? I've tried method injection, but to no avail.
I forgot to explain that what I'm trying to achieve is a kind of chained injection where an instance of class PatientRecordSummary gets injected with an instance of MockPatientRecordLocator (using constructor injection) and said instance of MockPatientRecordLocator should get injected with an instance of IContactAdapter (again using constructor injection (if possible)). The first part of the chain works, the second doesn't.
Not bad for a first question!
You want to use the Bind(Type) overload to allow registration of stuff that you dont have statically available in the context of your Load() code - do the stuff you're doing in your provider (i.e., resolving the Type) up-front. This will allow Ninject to do the object instantiation (without any requirement for a default .ctor)
IIRC two or 3 of my most recent answers also touch on this discovery/loading stuff, and have examples that should be relevant to your case.
(And you wont need to resort to [Inject] attributes when you've gotten to remove things)
Is it a violation of the Persistance igorance to inject a repository interface into a Entity object Like this. By not using a interface I clearly see a problem but when using a interface is there really a problem? Is the code below a good or bad pattern and why?
public class Contact
{
private readonly IAddressRepository _addressRepository;
public Contact(IAddressRepository addressRepository)
{
_addressRepository = addressRepository;
}
private IEnumerable<Address> _addressBook;
public IEnumerable<Address> AddressBook
{
get
{
if(_addressBook == null)
{
_addressBook = _addressRepository.GetAddresses(this.Id);
}
return _addressBook;
}
}
}
It's not exactly a good idea, but it may be ok for some limited scenarios. I'm a little confused by your model, as I have a hard time believing that Address is your aggregate root, and therefore it wouldn't be ordinary to have a full-blown address repository. Based on your example, you probably are actually using a table data gateway or dao rather than a respository.
I prefer to use a data mapper to solve this problem (an ORM or similar solution). Basically, I would take advantage of my ORM to treat address-book as a lazy loaded property of the aggregate root, "Contact". This has the advantage that your changes can be saved as long as the entity is bound to a session.
If I weren't using an ORM, I'd still prefer that the concrete Contact repository implementation set the property of the AddressBook backing store (list, or whatever). I might have the repository set that enumeration to a proxy object that does know about the other data store, and loads it on demand.
You can inject the load function from outside. The new Lazy<T> type in .NET 4.0 comes in handy for that:
public Contact(Lazy<IEnumerable<Address>> addressBook)
{
_addressBook = addressBook;
}
private Lazy<IEnumerable<Address>> _addressBook;
public IEnumerable<Address> AddressBook
{
get { return this._addressBook.Value; }
}
Also note that IEnumerable<T>s might be intrinsically lazy anyhow when you get them from a query provider. But for any other type you can use the Lazy<T>.
Normally when you follow DDD you always operate with the whole aggregate. The repository always returns you a fully loaded aggregate root.
It doesn't make much sense (in DDD at least) to write code as in your example. A Contact aggregate will always contain all the addresses (if it needs them for its behavior, which I doubt to be honest).
So typically ContactRepository supposes to construct you the whole Contact aggregate where Address is an entity or, most likely, a value object inside this aggregate.
Because Address is an entity/value object that belongs to (and therefore managed by) Contact aggregate it will not have its own repository as you are not suppose to manage entities that belong to an aggregate outside this aggregate.
Resume: always load the whole Contact and call its behavior method to do something with its state.
Since its been 2 years since I asked the question and the question somewhat misunderstood I will try to answer it myself.
Rephrased question:
"Should Business entity classes be fully persistance ignorant?"
I think entity classes should be fully persistance ignorant, because you will instanciate them many places in your code base so it will quickly become messy to always have to inject the Repository class into the entity constructor, neither does it look very clean. This becomes even more evident if you are in need of injecting several repositories. Therefore I always use a separate handler/service class to do the persistance jobs for the entities. These classes are instanciated far less frequently and you usually have more control over where and when this happens. Entity classes are kept as lightweight as possible.
I now always have 1 Repository pr aggregate root and if I have need for some extra business logic when entities are fetched from repositories I usually create 1 ServiceClass for the aggregate root.
By taking a tweaked example of the code in the question as it was a bad example I would do it like this now:
Instead of:
public class Contact
{
private readonly IContactRepository _contactRepository;
public Contact(IContactRepository contactRepository)
{
_contactRepository = contactRepository;
}
public void Save()
{
_contactRepository.Save(this);
}
}
I do it like this:
public class Contact
{
}
public class ContactService
{
private readonly IContactRepository _contactRepository;
public ContactService(IContactRepository contactRepository)
{
_contactRepository = contactRepository;
}
public void Save(Contact contact)
{
_contactRepository.Save(contact);
}
}