Re: [Py4j-users] How do I cast Java objects between types on the Python side?

[Barthelemy D. <bar...@in...>]

Hi Chris,

glad you could fix it! I was replying with exactly this solution when
I saw you had sent a follow up.

Barthélémy

On Sat, Sep 7, 2013 at 1:53 AM, Chris Akins <chr...@gm...> wrote:
> Hi, all.
> Issue's resolved. I had to create the array of HGHandles that the
> constructor was expecting by hand, so
> Java:
> x=new HGValueLink("asdf", h1, h2)
>
> became Python:
> a=new_array(HGHandle, 2);
> a[0]=h1;
> a[1]=h2;
> x=gateway.jvm.org.hypergraphdb.hGValueLink("asdf",a)
>
> Thanks for your hard work.
>
> -Chris
>
>
> On Sat, Sep 7, 2013 at 12:16 AM, Chris Akins <chr...@gm...> wrote:
>>
>> Hi all.
>>
>> I'm trying to implement this code in Python: (from
>> http://www.hypergraphdb.org/learn?page=IntroStoreData&project=hypergraphdb
>> at the bottom, modified so I don't have to implement a class on the Java
>> side)
>>
>> bookHandle = graph.add("asdf")
>> priceHandle = graph.add(9.95)
>> link = new gateway.jvm.org.hypergraphdb.HGValueLink("price", bookHandle,
>> priceHandle)
>>
>>
>>
>>
>>
>> The problem is that in the Python code, the call to graph.add() from the
>> Python side is yielding an object of type
>> WeakHandle that implements HGLiveHandle, and HGValueLink only accepts
>> HGHandle[] in its arguments. The end result is
>>
>>
>>
>> that the java side throws an exception saying that a HGValueLink
>> constructor doesn't exist that takes
>> [String, handle.WeakHandle, handle.WeakHandle].
>>
>> (Relevant javadocs at
>> http://www.kobrix.com/javadocs/hgcore/org/hypergraphdb/HGValueLink.html,
>>
>>
>>
>> http://www.kobrix.com/javadocs/hgcore/org/hypergraphdb/HyperGraph.html,
>>
>> http://www.kobrix.com/javadocs/hgcore/org/hypergraphdb/handle/HGLiveHandle.html
>> )
>>
>>
>>
>> In the linked example the two handles are declared as HGHandle when
>> they're instantiated, so there's no problem when the method call does
>> typechecking.
>>
>>
>>
>> It seems to me, then, that the easiest way to rectify this is to use some
>> facility of the Gateway to re-cast the object returned from graph.add() as
>> HGHandle, and then just pass that the the HGValueLink constructor as it
>> wants.
>>
>>
>>
>> Can I do that from the gateway as it exists, or do I have to add a method
>> to my server code to cast it? Am I missing an easier and more obvious
>> solution in my Java inexperience?
>>
>>
>>
>> Thanks,
>> Chris
>>
>
>
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