I need help in retrieving query results within when clause of drl file in drools.
Example rule file having query:
query getUsersForCard (Long ipCardNumber)
$listOfUsers : UsersList()
$listOfUserCards : User(cardNumber == ipCardNumber, $cardNum : cardNumber) from $listOfUsers.user_list
end
rule "matchUser"
when
getUsersForCard("4444333322221112L";)
then
System.out.println( "$$$card number in VisaMessage matched with card number in UsersList$$$" );
end
How to obtain $cardNum aftergetUsersForCard query call so that then clause gets printed? I don't want to retrieve $cardNum in Java code from Working Memory but rather should be able to do it within the drl file itself.
Help is much appreciated!
Going back to the original question: "Can query results be accessed from the LHS of a rule?", the answer is: "Yes, using unification (Sections 8.8.3.3.6 and 8.9)".
A query in Drools can have input and output parameters. Input parameters are those that have a value (are bound) when the query is invoked. Those parameters that don't have a value (unbound) are considered output parameters.
The first thing to do is to rewrite your query using unification:
query getUsersForCard (Long ipCardNumber, Long $cardNum)
$listOfUsers : UsersList()
$listOfUserCards : User(
cardNumber == ipCardNumber,
$cardNum := cardNumber
) from $listOfUsers.user_list
end
The important thing to notice is the := (unification) sign being used. This operator is basically saying: "If the variable has a value, then I'll act as an == operator. Otherwise I'll act as a variable binding.
When invoking your query from a rule, you need to make sure you don't provide any value for the second parameter in the query. Given that you are already using positional arguments, that's easy to do:
rule "matchUser"
when
getUsersForCard("4444333322221112L", $cardNum;)
then
System.out.println( "$$$card number in VisaMessage matched with card number in UsersList$$$: "+$cardNum );
end
When the query is invoked, $cardNum will not have a value and it will set by the query because of the unification mechanism.
Hope it helps,
You cannot retrieve query results within the when clause the way I think you think it can be done. But there is no need to do so, simply write the rule as
rule "match card number"
when
$listOfUsers: UsersList()
$user: User(cardNumber == "4444333322221112L") from $listOfUsers
then ... end
Assuming the text of the println indicates what you really want to do, you might use
rule "match card number"
when
VisaMessage( $cardNo: cardNumber )
$listOfUsers: UsersList()
$user: User(cardNumber == $cardNo) from $listOfUsers
then ... end
Related
I use two string formulas in my details section to determine which countries to suppress. Formula1 refers to the Company field, and I suppress certain values:
{Countries}
In Formula2 i call a function with a parameter like #Formula1:
function(#formula1)
But the problem is that the function still takes the suppressed countries into account. Is this normal behavior, or do I need something extra like whileprintingdata to narrow my results.
When i debug the function the first time the function is called the incoming string is country1 even though I specified it to suppress that one. How can I ensure only unsuppressed values are passed to the function?
You could write additional logic into Formula2 to perform the same check that Formula1 does. Something like:
IF ({Countries} = 10) THEN
function("Company A")
ELSE IF ({Countries} = 14) THEN
function("Company B")
// ELSE IF....
ok got it your edit makes it clear...
what you can do is use the same supress condition in your formula 2 and pass the value to function.
some thing like below:
if your supress condition is
if {Countries} in (10,11,12)
then true
else false
then use the same in function 2 as
if {Countries} <> (10,11,12)
then function(formula1)
else any message as you wish
here is the sample that i want to ask:
FOR EACH table-name.... NO LOCK BY (IF TRUE THEN sort-this ELSE sort-that + sort-that2).
END.
This would result in an error.
if it is just
FOR EACH .. NO LOCK BY (IF TRUE THEN sort-this ELSE sort-that).
END.
then there is no error. Progress would accept the code
What is need is if condition is true then sort by one field else sort by two or more fields
If you are in a modern enough version of Progress, then you could construct a dynamic query. This will be more efficient in terms of run time as well as getting you round your problem as having IF statements in your query predicate will make index selection hard.
QueryString = "for each table no-lock...".
if true then
QueryString = QueryString + " by sort-this".
else
QueryString = QueryString + " by sort-that by sort-other".
create query QueryHandle.
QueryHandle:add-buffer(buffer table:handle).
QueryHandle:query-prepare(QueryString).
QueryHandle:query-open.
do while QueryHandle:get-next():
/*some stuff*/
end.
QueryHandle:query-close.
delete object QueryHandle.
As per the previous reply, this is not supported.
Typically, you'd have to prepare the result into a temp-table first, using a logical field in the temp-table for the result of your IF THEN ELSE expression.
Unfortunately, this syntax is not supported. As per the documentation, BREAK/BY expects an expression following it but not a statement.
I have different rules defined in DRL text files and XLS spreadsheet files. My XLS rules are executed first I am not able to understand why. The example is to manage a form with different categories and answers. The answer has a score that is used to return the user some information.
My first DRL rule is to sum all scores from all questions in a category:
package Form;
import ...;
rule "Sum Category Score"
salience 500
when
$form : SubmittedForm();
$cat : CategoryWithScore(score == null) from $form.categories;
$categoryScore : Number() from
accumulate($q : Question() from $cat.getQuestions(),
init( int $total = 0 ),
action( $total += $q.getAnswer().getScore(); ),
reverse( $total -= $q.getAnswer().getScore(); ),
result( $total )
);
then
$cat.setScore($categoryScore);
end
And with a XLS file, I define the result of a category depending on the total score.
As we can see, the DRL file has salience 500 and the XLS file has salience 250. Then I expect that the DRL rule is executed first.
If I print the XLS in rule format, everything seems correct:
package ScoreClassification;
//generated from Decision Table
import ...;
no-loop true
salience 250
// rule values at B13, header at B8
rule "Form Score Classification_13"
when
$form : SubmittedForm(); $cat : CategoryWithScore($cat.getText() == 'Cat1', $cat.getScore() >= 0, $cat.getScore() < 40) from $form.getCategoriesWithScore();
then
$cat.setResult('Good');
end
// rule values at B14, header at B8
...
I have put some simple System.out.println in the methods getScore and setScore of the category, to see what is happening. And I can see that getScore is executed first! (and has null value) and later setScore that assign correctly the value.
Why salience is not respected?
Three things.
First, you must use modify to effect a change of a fact in working memory.
rule "Sum Category Score"
...
then
modify( $cat ){ setScore( $categoryScore ) }
end
Otherwise, rule evaluation will never see the changed value.
Added after OPs 1st comment
Second, if the modification is in an object held in a collection within a fact and extracted using from, things begin to get murky. I avoid this, and recommend you to do the same. Insert the CategoryWithScore facts, and your problem is solved. (You may have to ascertain that the selected CategoryWithScore facts belong to the same SubmittedForm, if there is more than one form in WM at the same time.)
Third, it is a common misconception that priority (or salience) has an effect on the ordere of left hand side evaluations, and can be used to delay the evaluation of a rule where, constraint expressions may run into NPEs. It is best practice to write constraints so that null values result in a short-circuited false.
If you think that this clutters rules: yes, you are right. But even pure Java code is more robust when class members are set to some default or out-of-band value (might be -1 in your case) rather than left at null.
My requirement is to match tags. In the example, this particular HourConstraint checks the TeacherHour assigned to Hour(23).
Specifically, it checks TeacherHour.attributes["tags"] for the values ["asst_ct","teacher_john_smith"] and detects atleast one match, two in this case (both "asst_ct" and "teacher_john_smith") .
TeacherHour:
id: 47
assigned_hour: Null
attributes:Map<List<String>>
"tags":["asst_ct","no_strenuous_duties","kinda_boring","teacher_john_smith"]
"another_attribute":[...]
HourConstraint:
hour: Hour(23)
attribute: "tags"
values_list: ["asst_ct","teacher_john_smith"]
Question: How do I detect the presence (true or false) of common elements between two lists?
Drools Expert has memberOf and contains, but they check a scalar vs a collection, never a collection vs a collection.
I see two potential ways:
introduce a function boolean isIntersecting(list,list) and tell Drools to use that for truth checking
Implement TeacherHour.attributes[] as a string instead of a list and HourConstraint.valueslist as a regular expression that can match that list
There are a few options. Most straight forward is to use the Collections class to do that for you:
rule X
when
$t: TeacherHour( )
HourConstraint( Collections.disjoint( $t.attributes["tags"], values_list ) == false )
...
If this is something you would use often in your rules, then I recommend wrapping that function in a pluggable operator, supported by Drools. Lets say you name the operator "intersect", you can then write your rules like this:
rule X
when
$t: TeacherHour( )
HourConstraint( values_list intersect $t.attributes["tags"] )
...
A third option, is to use "from", but that is less efficient in runtime as it causes iterations on the first list:
rule X
when
$t: TeacherHour( )
$tag : String() from $t.attributes["tags"]
exists( HourConstraint( values_list contains $tag ) )
...
I have an ArrayList in working memory that I am iterating with a 'from' statement in my when clause. However, the rule is iterating backwards through the array. Is there a way to control this behavior?
List Creation:
List<Map<String,String>> list = new ArrayList<Map<String,String>>();
Map<String,String> m1 = ...
Map<String,String> m2 = ...
list.add(m1);
list.add(m2);
ImportItem item = new ImportItem(list); //model object. Constructor arg returned by getInput()
StatelessKnowledgeSession session = knowledgeBase.newStatelessKnowledgeSession();
session.insert(item);
session.fireAllRules();
Drools rules:
rule "My Rule"
dialect "java"
when
item : ImportItem(ignore == false) //model object that holds the input
map : Map() from item.getInput() // == the ArrayList from above
then
System.out.println(map);
end
Produces
<output of m2>
<output of m1>
The iteration is not backwards, as you can see if you attach an audit log to your session. The execution of the rules is what follows, by default, a LIFO order (in case you are not using any other conflict resolution strategy).
My suggestion for you is don't try to encapsulate the objects in data structures. If you are reading lines of a file and you need to process these lines in order, just use a class to represent the line and insert the lines directly into the session. To guarantee execution order, you can use the line number as a parameter to salience.
For instance:
rule "Process lines in order"
// salience executes from higher number to lowest number, so using the
// negative value you will executem them from the first to the last
salience (- $lineNumber )
when
$line : Line( $lineNumber : lineNumber )
then
// do something with $line
end
Obviously the same trick can be used with the "from" approach you took, but the engine is much more efficient matching facts in the working memory than it is iterating over collections of objects.
Hope it helps.
Edson
You should always try to write the rules so that the order doesn't count. If however, you really really need to have rules firing in certain order, or in this case, get the facts from a list in a certain order. Make sure that whatever changes in the rule engine internals doesn't break up your rules when you update to a newer version of the engine.
You can't trust the "from" even if it did the iteration the other way around.
There is one problem with this solution. If you update the ImportItem and need to iterate through the input again, you need to retract the MyIterator that is related to it.
declare MyIterator
index:int
lastIndex:int
importItem:ImportItem
end
rule "Insert ImportItem iterator"
when
item : ImportItem()
not MyIterator( importItem == item )
then
MyIterator myIterator = new MyIterator();
myIterator.setImportItem( item );
myIterator.setIndex( 0 );
myIterator.setLastIndex( item.getInput().size() );
insert( myIterator );
end
rule "My Rule"
when
myIterator :MyIterator( index < lastIndex )
item : ImportItem( this == myIterator.importItem,
ignore == false )
map : Map() from item.getInput().get( myIterator.getIndex() )
then
System.out.println(map);
myIterator.setIndex( myIterator.getIndex() + 1 );
update( myIterator );
end