4:59 p.m.
I am currently using Drools Server to accept JSON-formatted insertion
messages from a PHP application. Within the DRL file, I am currently
declaring the insertion object (let's use Person, for example) using
"Declare", e.g.,
declare Person
name: String
address: AddressType
end
declare AddressType
...
end
My question is, how do you declare an array object (e.g., "Hobbies") that
can be nested within Person. I have scanned the Internet (once again!) for
longer than I care to admit and have found no examples for this simple
usage. I have unsuccessfully tried multiple variations in defining an
array, but have given up. My current intention is to avoid using externally
defined Java, if possible, and I would like to be able to define the
insertion object within the DRL to enable quick changes in the incoming JSON
format, if necessary (I know this might not be "best practice"!). Could
someone please provide me with a quick example.
Thanks! Fulton
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2:06 a.m.
Array types are not supported for the fields of types declared in DRL.
A java.util.ArrayList (no generic parameters) should work.
-W
On 26 April 2011 23:59, fulton <fulton.gee(a)lmco.com> wrote:
I am currently using Drools Server to accept JSON-formatted
insertion
messages from a PHP application. Within the DRL file, I am currently
declaring the insertion object (let's use Person, for example) using
"Declare", e.g.,
declare Person
name: String
address: AddressType
end
declare AddressType
...
end
My question is, how do you declare an array object (e.g., "Hobbies") that
can be nested within Person. I have scanned the Internet (once again!) for
longer than I care to admit and have found no examples for this simple
usage. I have unsuccessfully tried multiple variations in defining an
array, but have given up. My current intention is to avoid using
externally
defined Java, if possible, and I would like to be able to define the
insertion object within the DRL to enable quick changes in the incoming
JSON
format, if necessary (I know this might not be "best practice"!). Could
someone please provide me with a quick example.
Thanks! Fulton
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4:06 p.m.
Wolfgang,
Thanks again for the reply! However, after much testing, I'm still having
problems with Drools Server parsing the JSON array. My current test DRL is:
==============================
package com.foobar
declare Person
name: String
hobbies: java.util.ArrayList
end
rule "Person" dialect "mvel"
when
$p : Person();
then
$p.name = $p.name + " has hobby size of " + $p.hobbies.size();
end
===============================
and my current JSON msg sent to the Drools Server (via TCPMON) is:
===============================
{
'insert':
{
'out-identifier': '123',
'object':
{
'com.foobar.Person':
{
"name":"fulton",
"hobbies":
[123]
}
}
}
}
==============================
The above JSON will be inserted successfully, but the result shows that
$p.hobbies.size() returns "0". If I add another element to the JSON array
(e.g., [123,345]), I get the following Xstream exception:
==============================
com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter$DuplicateFieldException:
hobbies
---- Debugging information ----
duplicate-field : hobbies
class : org.drools.command.runtime.rule.InsertObjectCommand
required-type : com.foobar.Person
line number : -1
-------------------------------
at
com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter$SeenFields.add(AbstractReflectionConverter.java:322)
at
com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.doUnmarshal(AbstractReflectionConverter.java:234)
===============================
If I modify the JSON array to contain objects (e.g.,
[{"abc":"123"},{"cdf":"345"}]), which is what
I'm ultimately desiring, then
I get the following exception:
===============================
com.thoughtworks.xstream.converters.ConversionException: 123 : 123 : 123 :
123
---- Debugging information ----
message : 123 : 123
cause-exception :
com.thoughtworks.xstream.mapper.CannotResolveClassException
cause-message : 123 : 123
class : org.drools.command.runtime.rule.InsertObjectCommand
required-type : java.util.ArrayList
line number : -1
-------------------------------
at
com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:89)
at
com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:76)
===============================
Am I missing something in the DRL declaration? Do the array elements need
to be declared somehow (if so, how?)? Can Xstream unmarshal the JSON array
into an ArrayList?
I can move this thread to the Xstream forum (if there is one), if you'd
like, but if there's a simple answer here, then I'd greatly appreciate it!
Thanks again for your help!
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1:36 p.m.
(email subscribers) In reference to my question on how to declare an array
field within a class defined in the "declare" section of a DRL file (for use
within the Drools Server):
Well, it took me 2 days to figure it out, but here is the current answer. I
ended up just processing things in reverse with XStream to see what it was
expecting. That is, I created a Java tester to manually define my Person
and Hobby classes, and then instantiated a Person object and marshalled it
into JSON with XStream to see what it should look like. I then reversed the
process to unmarshall the JSON back into a Java object to verify that
XStream would parse it correctly. The trick was to specify the nested Hobby
objects correctly. There's no way I could have figured this out without
generating the JSON with XStream FIRST.
DRL:
==============================
package com.foobar
declare Hobby
name: String
desc: String
end
declare Person
name: String
hobbies: java.util.ArrayList
end
rule "Person" dialect "mvel"
when
$p : Person();
then
$p.name = $p.name + " has hobby size of " + $p.hobbies.size();
end
===============================
JSON to be generated from the PHP application:
===============================
{
'insert':
{
'out-identifier':'123',
'object':
{
'com.foobar.Person':
{
"name":"Joe",
"hobbies":
[
{
"com.foobar.Hobby":
[
{"name":"Golf","desc":"Sport #1"},
{"name":"Bowling","desc":"Sport #2"}
]
}
]
}
}
}
}
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fulton -
Wolfgang Laun