I'm trying to figure out how to support multi-valued properties with the Tinkerpop Frames API. I have an interface like this:
interface Node {
#Property("synonyms")
public Iterable<String> getSynonyms();
#Property("synonyms")
public void addSynonym(String synonyms);
}
The addSynonym call doesn't throw any exceptions but the getSynonyms alyways returns null. I also tried switching Iterable to Collection with no change.
Does Frames support multi-valued properties?
#Property in Frames does not support collection semantics as Tinkerpop 2.x does not allow this. It simply gets or sets the property on the underlying element.
The method prefixes supported for #Property are get, is, can, set and remove
https://github.com/tinkerpop/frames/wiki/Core-Annotations
You could write your own method handler that supports this:
https://github.com/tinkerpop/frames/wiki/Method-Handlers
Related
In JsonDeserialize annotation documentation the contentAs field is supposed to define the "Concrete type to deserialize content".
I tried to use this in combination, with either a Converter (via contentConverter field of the same annotation) or a JsonDeserializer (via contentUsing field of the same annotation), by extending either StdConverter or StdDeserializer, respectively, in an attempt to create an agnostic custom deserializer.
I cannot find a way to access the JsonDeserialize#contentAs information inside any of these two classes.
I am aware that the classes I extend from have a type parameter, I just put an Object class there. Documentation states
contentAs Concrete type to deserialize content (elements of a Collection/array, values of Maps) values as, instead of type otherwise declared. Must be a subtype of declared type; otherwise an exception may be thrown by deserializer.
Apparently I am applying the #JsonDeserializer annotation on a Collection of some persistable Class. I want to deserialize each such object, solely by knowing its id. Well, if I could only get that very type I defined in the #JsonDeserializer#contentAs field...
Can anyone tell me if this is possible anyhow?
I managed to implement the agnostic deserializer withou the use of #JsonDeserializer#contentAs after all.
After reading the javadocs of com.fasterxml.jackson.databind.JsonDeserializer I concluded that my custom deserializer should implement the com.fasterxml.jackson.databind.deser.ContextualDeserializer interface.
Inside the implementation of ContextualDeserializer#createContextual(DeserializationContext ctxt, BeanProperty property)
I could finally get access to the class type of the content of the collection, which I applied the #JsonDeserialize annotation on,
by calling:
ctxt.getContextualType().getRawClass()
NOTE that the same call inside the implementation of com.fasterxml.jackson.databind.JsonDeserializer#deserialize(com.fasterxml.jackson.core.JsonParser, com.fasterxml.jackson.databind.DeserializationContext) returned null, hence the need of the aforementioned interface.
All I had to do then is store the returned class in a member field (of type Class< ? >) of the custom deserializer and use it in the execution of JsonDeserializer#deserialize()
The only thing that remains to check is whether an instance of this custom deserializer is shared between threads. I only did some minor checks; I used the same implementation for two different collections of different types. I observed that ContextualDeserializer#createContextual(DeserializationContext ctxt, BeanProperty property) was called once (among multiple deserialization invokations), for each distinct type that was going to be deserialized. After checking during debugging, it seems that the same deserializer object is used for the same type. In my case, since what I store in the member field is this type itself, I don't mind if the same deserializer is used for the same java type to be deserialized because they should contain the same value. So we 're clear on this aspect as well.
EDIT: It appears all I have to do is update the com.fasterxml.jackson.databind.deser.std.StdDeserializer#_valueClass value to the now known class. Since it is final and since the ContextualDeserializer#createContextual(DeserializationContext ctxt, BeanProperty property) returns a JsonSerializer object, which is actually used,
instead of returning "this" serializer I can create a new one, passing the discovered class in the constructor, which actually sets the StdDeserializer#_valueClass to the class I actually want, and I'm all set!
Finally, NOTE that I didn't have to use the #JsonDeserializer#contentAs annotationfield as I get the value from the ctxt.getContextualType().getRawClass() statement inside ContextualDeserializer#createContextual(DeserializationContext ctxt, BeanProperty property) implementation
I am designing a process that should be run daily at work, and I've written a class to do the work. It looks something like this:
class LeadReport {
public $posts = array();
public $fields = array();
protected _getPost() {
// get posts of a certain type
// set them to the property $this->posts
}
protected _getFields() {
// use $this->posts to get fields
// set $this->fields
}
protected _writeCsv() {
// use the properties to write a csv
}
protected _sendMail() {
// attach a csv and send it
}
public function main() {
$this->out('Lead Report');
$this->out("Getting Yesterday's Posts...");
$this->_getPosts();
$this->out("Done.");
$this->out("Next, Parsing the Fields...");
$this->_getFields();
$this->out("Done.");
$this->out("Next, Writing the CSVs...");
$this->_writeCsv();
$this->out("Done.");
$this->out("Finally, Sending Mail");
$this->_sendMail();
$this->out('Bye!');
}
}
After showing this code to one of my colleagues, he commented that the _get() methods should have return values, and that the _write() and _sendMail() methods should use those values as parameters.
So, two questions:
1) Which is "correct" in this case (properties or return values)?
2) Is there a general rule or principle that governs when to use properties over when to use return values in object oriented programming?
I think maybe the source of your question comes from the fact that you are not entirely convinced that using properties is better than having public fields. For example here, common practice says that should not have posts and fields as public. You should use the getField method or a Field protected property to regulate access to those fields. Having a protected getField and a public fields doesn't really make sense.
In this case your colleague may be pointing at two things. The fact that you need to use Properties and not public fields and also the fact that it is probably better to pass the post into the method and not have the method access a property if you can. That way you don't have to set a property before calling the method. Think of it as a way of documenting what the method needs for it to operate. In this way another developer doesn't need to know which properties need to be set for the method to work. Everything the method needs should be passed in.
Regarding why we need properties in the first place? why shouldn't you use public fields. Isn't it more convenient? It sure is. The reason we use properties and not public fields is that just like most other concepts in OOP, you want your object to hide its details from the outside world and just project well defined interfaces of its state. Why? Ultimately to hide implementation details and keep internal change to ripple out(Encapsulation). Also, accessing properties has the added benefit of debugging. You can simply set a breakpoint in a property to see when a variable is changed or simply do a check if the variable is of certain value. Instead of littering your code with said check all over the place. There are many more goodies that come with this, returning readonly values, access control, etc.
To sum up, fields are though of as internal state. Properties(actual get/set methods) are though of as methods that interact with internal state. Having an outside object interact with interfaces is smiley face. Having outside class interact with internal state directly is frowny face.
I am searching around for a solution to my problem but all I get is the reasons this does happen as opposed to preventing if from happening.
I have a class, WorkflowActivityInstance which has a collection of WorkflowActivityInstanceTransitions which represents the transitioning of the state of the workflow. The transitions are mapped in a Transitions property fine.
Therefore: WorkflowActivityInstance <-- WorkflowActivityInstanceTransition
I would like a view on the object which would give the WorkflowActivityInstance state including its current state, which would simply be the latest WorkflowActivityInstanceTransition without having the user-coder to perform their own sorting and selection on the Transitions property.
Originally, I had:
public virtual IWorkflowActivityInstanceTransition CurrentState
{
get { return Transitions.OrderBy(q => q.TransitionTimeStamp).LastOrDefault(); }
}
But I just get:
NHibernate.InvalidProxyTypeException:
NHibernate.InvalidProxyTypeException: The following types may not be
used as proxies:
FB.SimpleWorkflow.NHibernate.Model.WorkflowActivityInstance: method
CurrentState should be 'public/protected virtual' or 'protected
internal virtual'.
I tried to be cheeky and convert this to a method:
public IWorkflowActivityInstanceTransition GetCurrentState()
{
return Transitions.OrderBy(q => q.TransitionTimeStamp).LastOrDefault();
}
But I get a very similar:
NHibernate.InvalidProxyTypeException:
NHibernate.InvalidProxyTypeException: The following types may not be
used as proxies:
FB.SimpleWorkflow.NHibernate.Model.WorkflowActivityInstance: method
GetCurrentState should be 'public/protected virtual' or 'protected
internal virtual'.
I would like to keep the very simple behaviour of CurrentState in my model class, and prevent NHibernate from over-reaching itself and trying to map/proxy this property. It feels that this should just be an attribute on the property I don't want to map ...
How can I achieve this?
NHibernate needs to override all public, protected and internal methods, otherwise proxies can't work (it would be possible for your code to access a not yet initialized proxy).
I can't see a reason why your property wouldn't work, but the error is very clear for your method, you miss the virtual keyword.
You must to use virtual keyword. This is how it work of Nhibernate. And also this page will help you.
Github nhibernate/nhibernate-core
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
Resolving a class that has multiple constructors with NInject doesn't seem to work.
public class Class1 : IClass
{
public Class1(int param) {...}
public Class1(int param2, string param3) { .. }
}
the following doesn’t seem to work:
IClass1 instance =
IocContainer.Get<IClass>(With.Parameters.ConstructorArgument(“param”, 1));
The hook in the module is simple, and worked before I added the extra constructor:
Bind().To();
The reason that it doesn't work is that manually supplied .ctor arguments are not considered in the .ctor selection process. The .ctors are scored according to how many parameters they have of which there is a binding on the parameter type. During activation, the manually supplied .ctor arguments are applied. Since you don't have bindings on int or string, they are not scored. You can force a scoring by adding the [Inject] attribute to the .ctor you wish to use.
The problem you're having is that Ninject selects .ctors based on the number of bound parameters available to it. That means that Ninject fundamentally doesn't understand overloading.
You can work around this problem by using the .ToConstructor() function in your bindings and combining it with the .Named() function. That lets you create multiple bindings for the same class to different constructors with different names. It's a little kludgy, but it works.
I maintain my own software development blog so this ended up being a post on it. If you want some example code and a little more explanation you should check it out.
http://www.nephandus.com/2013/05/10/overloading-ninject/