Is there any sample Scala code available for creating stored procedures in Neo4j-3.0.3 ?
I have been trying to create one simple Scala based stored procedure. Below is the Error message I get when I copy my scala-jar file to the neo4j-plugins directory and start the neo4j server :
=================
Caused by: org.neo4j.kernel.lifecycle.LifecycleException: Component 'org.neo4j.kernel.impl.proc.Procedures#1ac0223' was successfully initialized, but failed to start. Please see attached cause exception.
at org.neo4j.kernel.lifecycle.LifeSupport$LifecycleInstance.start(LifeSupport.java:444)
at org.neo4j.kernel.lifecycle.LifeSupport.start(LifeSupport.java:107)
at org.neo4j.kernel.impl.factory.GraphDatabaseFacadeFactory.newFacade(GraphDatabaseFacadeFactory.java:140)
... 10 more
Caused by: org.neo4j.kernel.api.exceptions.ProcedureException: Unable to find a usable public no-argument constructor in the class `neoscala`. Please add a valid, public constructor, recompile the class and try again.
=================
The scala class that I have used is :
package neoproc
import org.neo4j.graphdb.GraphDatabaseService
import org.neo4j.procedure.Procedure;
import javax.ws.rs.core.{Context, Response}
class neoscala(#Context db: GraphDatabaseService) {
#Procedure
def alice():String = {
String.valueOf(db.execute( "MATCH (n:User) return n" ));
}
}
Your Scala class declares a constructor with a GraphDatabaseService argument, and the exception tells you that it only wants a no-argument constructor.
It's documented in both
the user documentation:
Only static fields and #Context-annotated fields are allowed in Procedure classes.
the Javadoc:
The procedure method itself can contain arbitrary Java code - but in order to work with the underlying graph, it must have access to the graph API. This is done by declaring fields in the procedure class, and annotating them with the Context annotation. Fields declared this way are automatically injected with the requested resource. This is how procedures gain access to APIs to do work with.
All fields in the class containing the procedure declaration must either be static; or it must be public, non-final and annotated with Context.
Apparently it's not possible to create a class with a public field in Scala, so you'll have to create a parent Java class with the public field, and extend it with your Scala class:
// ProcedureAdapter.java
public abstract class ScalaProcedureAdapter {
#Context
public GraphDatabaseService db;
}
// neoscala.scala
class neoscala extends ScalaProcedureAdapter {
// ...
}
Here is the solution for this :
We will create Class in scala :
class FullTextIndex extends JavaHelper {
#Procedure("example.search")
#PerformsWrites
def search(#Name("label") label: String,
#Name("query") query: String): Stream[SearchHit] = {
//declare your method
}
val nodes: Stream[Node] = db.index.forNodes(index).query(query).stream
val newFunction: java.util.function.Function[Node, SearchHit] = (node: Node) => new SearchHit(node)
nodes.map {
newFunction
}
}
private def indexName(label: String): String = {
"label-" + label
}
}
Procedure in Neo4j always return result in Stream and it is a latest feature in Java8 so we will also used Java Class for return the final result and For defining the public variable.
We will create Java class for result :
public class JavaHelper {
#Context
public GraphDatabaseService db;
#Context
public Log log;
public static class SearchHit {
//your result code here
}
You can refer knoldus blog for Neo4j User Defined Procedure for creating and storing Neo4j Procedure with Scala. Here you will also find sample code with git hub repository.
Related
I have created a library in C# to be used in Q# programs. The library has two scripts, a C# class library called "Class1.cs" and a matching Q# script called "Util.qs", I share the code snippet of each here:
Class1.cs:
using System;
using Microsoft.Quantum.Simulation.Common;
using Microsoft.Quantum.Simulation.Core;
using Microsoft.Quantum.Simulation.Simulators;
namespace MyLibrary {
class Class1 : QuantumSimulator {
static void Method_1 (string str) { ... }
.
.
.
}
}
Util.qs:
namespace MyLibrary {
operation Op_1 (str : String) : Unit { body intrinsic; }
}
There is another Q# program in a different namespace that uses the namespace "MyLibrary" so after adding reference, in this Q# program I have:
namespace QSharp
{
open Microsoft.Quantum.Canon;
open Microsoft.Quantum.Intrinsic;
open MyLibrary;
operation TestMyLibrary() : Unit {
Op_1("some string");
}
}
When I execute "dotnet run" in the terminal I receive this message:
Unhandled Exception: System.AggregateException: One or more errors
occurred. (Cannot create an instance of MyLibrary.Op_1 because it is
an abstract class.) ---> System.MemberAccessException: Cannot create
an instance of MyLibrary.Op_1 because it is an abstract class.
How can I fix it?
Thanks.
UPDATE:
Following Mariia' answer and also checking Quantum.Kata.Utils, I changed my code as following:
So, I changed Class1 script to:
using System;
using Microsoft.Quantum.Simulation.Common;
using Microsoft.Quantum.Simulation.Core;
using Microsoft.Quantum.Simulation.Simulators;
namespace MyLibrary {
class Class1 : QuantumSimulator {
private string classString = "";
public Class1() { }
public class Op_1_Impl : Op_1{
string cl_1;
public Op_1_Impl (Class1 c) : base (c) {
cl_1 = c.classString;
}
public override Func<string, QVoid> Body => (__in) => {
return cl1;
};
}
}
Now the error messages are:
error CS0029: Cannot implicitly convert type 'string' to 'Microsoft.Quantum.Simulation.Core.QVoid'
error CS1662: Cannot convert lambda expression to intended delegate type because some of the return types
in the block are not implicitly convertible to the delegate return type
Having checked Quantum.Kata.Utils, I realised I need to create a field and a constructor for Class1 which is a base class and also I should override Func<string, QVoid> as the Op_1 parameter is string type. But I am not sure if each of these steps individually is done properly?
Second Update:
I have changed the previous c# code in first update to the following one:
using System;
using Microsoft.Quantum.Simulation.Common;
using Microsoft.Quantum.Simulation.Core;
using Microsoft.Quantum.Simulation.Simulators;
namespace MyLibrary {
class Class1 : QuantumSimulator {
public Class1() { }
public class Op_1_Impl : Op_1{
Class1 cl_1;
public Op_1_Impl (Class1 c) : base (c) {
cl_1 = c;
}
public override Func<string, QVoid> Body => (__in) => {
return QVoid.Instance;
};
}
}
Now the error message is the same as the very first one:
Unhandled Exception: System.AggregateException: One or more errors
occurred. (Cannot create an instance of MyLibrary.Op_1 because it is
an abstract class.) ---> System.MemberAccessException: Cannot create
an instance of MyLibrary.Op_1 because it is an abstract class.
And also in this new code shouldn't the constructor public Class1() { } have a parameter? if so what datatype?
In your code, there is nothing connecting the Q# operation Op_1 and the C# code that you intend to implement it in Method_1.
Q# operations are compiled into classes. To define a C# implementation for a Q# operation with the intrinsic body, you have to define a class that implements the abstract class into which your Q# operation gets compiled; so you would have something like public class Op_1_Impl : Op_1.
Getting all the piping right can be a bit tricky (it's a hack, after all!) I would recommend looking at the operation GetOracleCallsCount and its C# implementation to see the exact pieces that have to be in place for it to work.
For the updated question, the signature of your method says that it takes string as an input and returns nothing (QVoid), but the implementation tries to return a string cl_1, so you get a Cannot implicitly convert type 'string' to 'Microsoft.Quantum.Simulation.Core.QVoid'.
To provide a custom C# emulation for your Op_1 Q# operation, you'll need to replace your Class1.cs with something like this:
using System;
using Microsoft.Quantum.Simulation.Core;
namespace MyLibrary
{
public partial class Op_1
{
public class Native : Op_1
{
public Native(IOperationFactory m) : base(m) { }
public override Func<String, QVoid> Body => (str) =>
{
// put your implementation here.
Console.WriteLine(str);
return QVoid.Instance;
};
}
}
}
You can then run the Test1Library using the QuantumSimulator.
That being said, as Mariia said, this is kind of hacky, undocumented functionality that might change in the future, may I ask why you need this?
I am getting com.google.gwt.user.client.rpc.SerializationException exception for HashSet.
Initially I thought either HashSet of Long is not supported.
But https://developers.google.com/web-toolkit/doc/latest/RefJreEmulation contains both of these.
What would be the problem?
I am posting the Service method here:
public Set<Long> getNamesFromIDs(Set<Long> ids) {
return manager.getNamesFromIDs(ids);
}
Here, manager is the reference to the Manager class which is included from a library.
I am posting the manager method too:
public Set<Long> getNamesFromIDs(Set<Long> styleIds) {
List<Long> listIDs = new ArrayList<Long>(styleIds);
Map<Long, Discount> personMap = personDAO.getStyleIdToDiscountMap(listIDs, 0);
return personMap.keySet();
}
Detailed Exception Message:
com.google.gwt.user.client.rpc.SerializationException: Type 'java.util.HashMap$KeySet'
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.: instance = [30002, 30001]
The above classes from java.util are serialized by the custom field serializer.
Serialization for the KeySet is not supported by GWT. It does not implement a Serializable interface ( so it is not serializable in java world either)
I'm loading a .NET assembly dinamically via reflection and I'm getting all the classes that it contains (at the moment one). After this, I'm trying to cast the class to an interface that I'm 100% sure the class implements but I receive this exception: Unable to cast object of type System.RuntimeType to the type MyInterface
MyDLL.dll
public interface MyInterface
{
void MyMethod();
}
MyOtherDLL.dll
public class MyClass : MyInterface
{
public void MyMethod()
{
...
}
}
public class MyLoader
{
Assembly myAssembly = Assembly.LoadFile("MyDLL.dll");
IEnumerable<Type> types = extension.GetTypes().Where(x => x.IsClass);
foreach (Type type in types)
{
((MyInterface)type).MyMethod();
}
}
I have stripped out all the code that is not necessary. This is basically what I do. I saw in this question that Andi answered with a problem that seems the same mine but I cannot anyway fix it.
You are trying to cast a .NET framework object of type Type to an interface that you created. The Type object does not implement your interface, so it can't be cast. You should first create a specific instance of your object, such as through using an Activator like this:
// this goes inside your for loop
MyInterface myInterface = (MyInterface)Activator.CreateInstance(type, false);
myInterface.MyMethod();
The CreateInstance method has other overloades that may fit your needs.
Is there a way to call a method in a Grails service, from a Scala class that is running on the same JVM?
I have seen something similar done from Groovy/Griffon but cannot figure out how to accomplish that in Grails. (http://www.jroller.com/aalmiray/entry/griffon_groovy_scala_working_together)
Basically, one of my Grails controllers calls some Scala code, which should return some values asynchronously. So, I guess, the only way to return those values is by calling back a method in a Grails service.
I found a way of doing it, inspired by the link in the question above, and one of the FAQs in the Grails website.
On the Scala side:
Declare an object similar to the following:
package scalaCallback
object ScalaCallback{
var cback: {def callback(example: String)} = null
def setCallback(cb: {def callback(example: String)}){
cback = cb
}
def invokeCallback(example: String){
if(callback != null) cback.callback(example)
}
}
On the Grails side:
Create a class in src/groovy similar to the following:
package groovyCallback
import org.codehaus.groovy.grails.commons.ApplicationHolder
class GroovyCallback{
private GroovyCallback() {}
private static final INSTANCE = new GroovyCallback()
static getInstance(){ return INSTANCE }
void callback(String example){
ApplicationHolder.application.mainContext.yourService.yourMethod(example)
}
}
In your BootStrap.groovy init add the following:
scalaCallback.cback = groovyCallback.GroovyCallback.getInstance()
When you call invokeCallback("example") in Scala, it will call yourService.yourMethod("example")
Note: the jar file with your Scala class should be in the lib folder of you Grails application
Your Grails service is a Spring bean. #Autowire the service into your Scala class (it will need to be a bean/#Component) and call the method.
EDIT - added example:
For example (using Java, not Scala but the approach is exactly the same):
Java code calling service:
package grailstest;
#Component
public class ServiceInjectionTester {
#Autowired TestService testService;
public String testTheService() {
return testService.serviceMethod();
}
}
Service:
class TestService {
String serviceMethod() {
return "success"
}
}
In Config.groovy:
grails.spring.bean.packages = [ "grailstest" ]
You can also wire your Java/Scala bean into your Grails classes:
class TestController {
#Autowired
ServiceInjectionTester serviceInjectionTester
def index = {
render(text: serviceInjectionTester.testTheService())
}
}
References:
Grails Reference 8.4 - Using Services from Java
Spring: The Foundation for Grails
I have a class that extends AbstractGinModule
like:
public class ClientModule extends AbstractGinModule {
public ClientModule() { }
#Override
protected void configure() {
...
...
bind(...class).annotatedWith(...).to(...class).in(Singleton.class);
...
}
}
The idea that I have is to bind one class with another class based on a value stored in a property file.
like:
param contains the value coming from the property file
if(param.equals("instanceB"))
bind(a.class).to(b.class)
else
bind(a.class).to(c.class)
I have a class that access this property file and return a string with the value.
This class is called: InstanceParameters.java
I would like to get an instance of this class within my ClientModule.
But I don't find any way to do it.
I tried with:
- InstanceParameters param = new InstanceParameters ();
- GWT.create(InstanceParameters.class); (Error because this method should only be used on the client side)
Is there a way to access this InstanceParameters class within this clientModule?
Thank you for your help
You don't need to read the file before launching the application - just before creating the AbstractGinModule (via GWT.create). So, load the Dictionary in your onModuleLoad method and pass the parameters, either as a whole InstanceParameters class or as the extracted String, via a provider or any other means.