4:30 a.m.
Hello,
In my rules file I'd like to set something like this:
rule "mayThrowDice"
when
$user : User($gp : gameplay)
$gameplay(this == $gp)
then
exists List<Boost>() {
..... some business logic
}
end
But it looks like there is no generics support. How can I make sure there is
a List of type Boost inserted into the session?
Thank you,
Martin
4:37 a.m.
2011/10/17 Martin A <wmlsub(a)gmail.com>:
Hello,
In my rules file I'd like to set something like this:
rule "mayThrowDice"
when
$user : User($gp : gameplay)
$gameplay(this == $gp)
then
exists List<Boost>() {
..... some business logic
}
This looks weird: "exists" is a conditional element which can't be
used on the right hand side (after "then").
end
But it looks like there is no generics support
Correct.
. How can I make sure there is
a List of type Boost inserted into the session?
You would have to write some code that detects any element in the List
that is not instanceof Boost, or some accumulate that produces true if
all elements are instanceof Boost.
-W
Thank you,
Martin
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4:37 a.m.
Java's generics are implemented by erasure,
which implies that there no information available at runtime that a
instance of a List is of a certain generic type, for example Boost.
So I don't think this is possible.
Note that some things do work in erasure IIRC, like the generic type of
a defined field in a class is available at runtime:
public class Foo {
private List<Bar> list;
}
but that's not useful in this case :)
Op 17-10-11 11:30, Martin A schreef:
Hello,
In my rules file I'd like to set something like this:
rule "mayThrowDice"
when
$user : User($gp : gameplay)
$gameplay(this == $gp)
then
exists List<Boost>() {
..... some business logic
}
end
But it looks like there is no generics support. How can I make sure
there is a List of type Boost inserted into the session?
Thank you,
Martin
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--
With kind regards,
Geoffrey De Smet
5:41 a.m.
Thanks for the prompt response!
Best regards,
Martin
2011/10/17 Geoffrey De Smet <ge0ffrey.spam(a)gmail.com>
**
Java's generics are implemented by erasure,
which implies that there no information available at runtime that a
instance of a List is of a certain generic type, for example Boost.
So I don't think this is possible.
Note that some things do work in erasure IIRC, like the generic type of a
defined field in a class is available at runtime:
public class Foo {
private List<Bar> list;
}
but that's not useful in this case :)
Op 17-10-11 11:30, Martin A schreef:
Hello,
In my rules file I'd like to set something like this:
rule "mayThrowDice"
when
$user : User($gp : gameplay)
$gameplay(this == $gp)
then
exists List<Boost>() {
..... some business logic
}
end
But it looks like there is no generics support. How can I make sure there
is a List of type Boost inserted into the session?
Thank you,
Martin
_______________________________________________
rules-users mailing
listrules-users@lists.jboss.orghttps://lists.jboss.org/mailman/listinfo/rules-users
--
With kind regards,
Geoffrey De Smet
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9:18 a.m.
Geoffrey is correct. Java erasure makes it impossible to match objects
based on generic types. It is also a best practice anyway to not use general
purpose collections as your business entities in your business model. Best
to use a properly defined business entity and then the generics issue is not
really an issue.
Edson
2011/10/17 Geoffrey De Smet <ge0ffrey.spam(a)gmail.com>
**
Java's generics are implemented by erasure,
which implies that there no information available at runtime that a
instance of a List is of a certain generic type, for example Boost.
So I don't think this is possible.
Note that some things do work in erasure IIRC, like the generic type of a
defined field in a class is available at runtime:
public class Foo {
private List<Bar> list;
}
but that's not useful in this case :)
Op 17-10-11 11:30, Martin A schreef:
Hello,
In my rules file I'd like to set something like this:
rule "mayThrowDice"
when
$user : User($gp : gameplay)
$gameplay(this == $gp)
then
exists List<Boost>() {
..... some business logic
}
end
But it looks like there is no generics support. How can I make sure there
is a List of type Boost inserted into the session?
Thank you,
Martin
_______________________________________________
rules-users mailing
listrules-users@lists.jboss.orghttps://lists.jboss.org/mailman/listinfo/rules-users
--
With kind regards,
Geoffrey De Smet
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Edson Tirelli
JBoss Drools Core Development
JBoss by Red Hat @ www.jboss.com
3:55 p.m.
Hello Edson,
If the generic *<T>* is not allowed, and drools appears to be written to
operate over collections of objects, how do you insert a List of items like
this:
*List<ProjectDataSet.Task> tasks*? In my code I insert the tasks as facts
like this:
*commands.add(CommandFactory.newInsertElements(tasks));*
I use a decision table and have as one of the variables: (in the variable
row)
*List<ProjectDataSet.Task> tasks*.
The error I receive is this:
/org.drools.template.parser.DecisionTableParseException: The format for
global variables is incorrect. It should be: [Class name, Class otherName].
But it was: [List<ProjectDataSet.Task> tasks]
at
org.drools.decisiontable.parser.RuleSheetParserUtil.getVariableList(RuleSheetParserUtil.java:84)/
I desire the rules in the table to iterate through all the tasks in that
list and identify tasks that are due soon (a part of my condition column
*TASKACTSTART< today* … etc. The TASKACTSTART is a field named by Microsoft
in the ProjectDataSet.Task class.)
Have I misunderstood the power of drools? How do you address a collection
of a type like List<T> in a rule?
Thank you in advance for your help,
Adrigan
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4:25 p.m.
Type Generics are used to control type cast conversion errors at compile time. In
runtime, it's just a List, not a List<T>. What is unique is that all the
contents of the List are of the same type. To define the global use:
Global List tasks
In rules, you can evaluate this as:
Rule 'some-rule'
When
$pds : ProjectDataSet() from tasks
Or you can add your contraints to the ProjectDataSet fact as needed. Collection tasks
could conceivable return several different object classes, but the Query Criteria states
to only inspect those Objects that are an instance of ProjectDataSet.
This would be synonymous to the following java process:
List<ProjectDataSet> pds = new ArrayList<ProjectDataSet>()
for(Object o : tasks) {
if ( o instanceof ProjectDataSet )
pds.add( (ProjectDataSet) o );
}
return pds;
However, in your java code that loads the fact, you are not setting a global, you are
inserting all members of the tasks collection into drools working memory.
This means, that your rule would evaluate those facts as:
Import com.some.project.path.ProjectDataSet
Rule 'some-rule'
When
$pds : ProjectDataSet()
Then
// some action
End
So in this case, you do not have a global, and you do not need to be concerned with the
fact you are loading in a List, because the function call you are calling is a helper
function that essentially does this:
for (Collection c : tasks) {
commands.add(CommandFactory.newInsert( c );
}
So what is in working memory, is a whole lot of ProjectDataSet objects, but not the list
itself. In reality, the actual code implementation of the function is not likely to be
what I have shown, but this is how you can think of the command's implementation.
Regards,
Armand
-----Original Message-----
From: rules-users-bounces(a)lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On
Behalf Of Adrigan
Sent: Thursday, November 17, 2011 1:56 PM
To: rules-users(a)lists.jboss.org
Subject: Re: [rules-users] How to handle generics in Drools?
Hello Edson,
If the generic *<T>* is not allowed, and drools appears to be written to operate
over collections of objects, how do you insert a List of items like
this:
*List<ProjectDataSet.Task> tasks*? In my code I insert the tasks as facts like
this:
*commands.add(CommandFactory.newInsertElements(tasks));*
I use a decision table and have as one of the variables: (in the variable
row)
*List<ProjectDataSet.Task> tasks*.
The error I receive is this:
/org.drools.template.parser.DecisionTableParseException: The format for global variables
is incorrect. It should be: [Class name, Class otherName].
But it was: [List<ProjectDataSet.Task> tasks]
at
org.drools.decisiontable.parser.RuleSheetParserUtil.getVariableList(RuleSheetParserUtil.java:84)/
I desire the rules in the table to iterate through all the tasks in that list and
identify tasks that are due soon (a part of my condition column *TASKACTSTART< today* …
etc. The TASKACTSTART is a field named by Microsoft in the ProjectDataSet.Task class.)
Have I misunderstood the power of drools? How do you address a collection of a type like
List<T> in a rule?
Thank you in advance for your help,
Adrigan
--
View this message in context:
http://drools.46999.n3.nabble.com/rules-users-How-to-handle-generics-in-D...
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12:55 a.m.
If someone else is also permitted to contribute a few pointers:
- You just mit the generic type parameter in DRL and all the files
compiled into it, including decision tables.
- Storing the List tasks as a global variable could be helpful, but I
don't see any reason for it when your rules should determine something
about the individual list elements. Data stored in a global variable is not
triggering any rules.
- If your rules should discover certain Task objects, then these objects
should be inserted as facts.
HTH
-W
On 17 November 2011 22:55, Adrigan <lillian.andres(a)lmco.com> wrote:
Hello Edson,
If the generic *<T>* is not allowed, and drools appears to be
written to
operate over collections of objects, how do you insert a List of items like
this:
*List<ProjectDataSet.Task> tasks*? In my code I insert the tasks as facts
like this:
*commands.add(CommandFactory.newInsertElements(tasks));*
I use a decision table and have as one of the variables: (in the variable
row)
*List<ProjectDataSet.Task> tasks*.
The error I receive is this:
/org.drools.template.parser.DecisionTableParseException: The format for
global variables is incorrect. It should be: [Class name, Class otherName].
But it was: [List<ProjectDataSet.Task> tasks]
at
org.drools.decisiontable.parser.RuleSheetParserUtil.getVariableList(RuleSheetParserUtil.java:84)/
I desire the rules in the table to iterate through all the tasks in
that
list and identify tasks that are due soon (a part of my condition column
*TASKACTSTART< today* … etc. The TASKACTSTART is a field named by
Microsoft
in the ProjectDataSet.Task class.)
Have I misunderstood the power of drools? How do you address a
collection
of a type like List<T> in a rule?
Thank you in advance for your help,
Adrigan
--
View this message in context:
http://drools.46999.n3.nabble.com/rules-users-How-to-handle-generics-in-D...
Sent from the Drools: User forum mailing list archive at Nabble.com.
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7 comments
6 participants
participants (6)
-
Adrigan -
Edson Tirelli -
Geoffrey De Smet -
Martin A -
Welsh, Armand -
Wolfgang Laun