I believe this is just another instance of the "a-STRING-is-not-a-
SYMBOL" problem. ValueVector.add(String) adds a Value of type
RU.SYMBOL to the ValueVector, whereas your JavaBean property is
going to be of type RU.STRING. The symbol and the String *don't*
match, so the second query returns no results. You want to say
new ValueVector().add(new Value("Hawkins", RU.STRING))
I put it to a vote on the list about 18 months ago whether Jess ought
to relax this restriction, and very surprisingly, most people who
responded wanted to keep things the way they are; perhaps they
misunderstood the question. I may have to make an executive decision
on this one and change things anyway.
On Mar 7, 2007, at 5:17 PM, B. Tenbergen wrote:
Hello List,
I have a problem with a query that I have written. For an Automatic
Course Scheduling System, I have created a query that checks each
fact in the working memory (which is a shadow fact of a Java-Course-
object) for the instructor name. Unfortunately, something goes
wrong, but I don't know what. Another query that finds all courses
starting at the same time works, though.
Let me show you an example. I am running the following code in a
main-method in a random class:
First, I create an Rete-object, an array that stores my query-
results and a vector of courses.
try {
Rete r = new Rete();
QueryResult[] results = new QueryResult[2];
Vector<Course> courseVector = new Vector<Course>();
I fill the vector with plain old java Course-objects. The first
field in each course is an course-ID (int), the second is the start
time (int) and the last one is the Instructor (String). Nothing
else is in the class (besides the get-methods for the above fields).
courseVector.addElement(new Course(1, 800, "Hawkins"));
courseVector.addElement(new Course(2, 800, "Einstein"));
courseVector.addElement(new Course(3, 1000, "Hawkins"));
Then, I define the Course-class in Jess and add the Course-objects
as shadow-facts to the working memory.
r.defclass("Course", "AutomaticScheduler.engine.Course",
null);
for (int i = 0; i < courseVector.size(); i++) {
r.definstance("Course", courseVector.elementAt(i), false);
}
After that, I define the queries... one for the start-time-
collision-detection and one to show every course by the same
instructor.
r.eval("(defquery detect-starttime-collision (declare
(variables ?var)) (Course (time_start ?var) (CRN ?crn)))");
r.eval("(defquery find-instructor (declare (variables ?
var)) (Course (instructor ?var) (CRN ?crn)))");
I run the queries and store the results in the array.
results[0] = r.runQueryStar("detect-starttime-collision",
new ValueVector().add(800));
results[1] = r.runQueryStar("find-instructor", new
ValueVector().add("Hawkins"));
Last, but not least, for every position in the array, I print out
the position number and the outcome of the result. At the end, it
is necessary to catch some exceptions, of course.
for (int i = 0; i < results.length; i++) {
System.out.println("results[" + i + "]:");
while (results[i].next()) {
System.out.println(results[i].getString("crn") + "
" + results[i].getString("var"));
}
}
}
catch (JessException je) {
je.printStackTrace();
}
}
So far so good. When I execute the code, the following lines are
output to the console:
results[0]:
1 800
2 800
results[1]:
That's it! The two courses with "Hawkins" as the instructor do not
come up! Although the result[] at position 1 is NOT null, it seems
to be empty; i.e. no course with that instructor name can be found.
This is still the case, if I do not query for the start time and/or
when I FIRST query for the instructor, THEN for the start time.
Actually, I expected the following as the output:
results[0]:
1 800
2 800
results[1]:
1 "Hawkins"
3 "Hawkins"
What is wrong? I believe it has got something to do with the fact
that I am query-ing for a String instead of an int (because the two
queries are basically the same). I really appreciate any help I can
get because at this point I seem not to be able to see the forest
due to all the trees ;-)
Thank you very much in advance for your help!
Bastian
---------------------------------------------------------
Ernest Friedman-Hill
Advanced Software Research Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
PO Box 969, MS 9012 [EMAIL PROTECTED]
Livermore, CA 94550 http://www.jessrules.com
--------------------------------------------------------------------
To unsubscribe, send the words 'unsubscribe jess-users [EMAIL PROTECTED]'
in the BODY of a message to [EMAIL PROTECTED], NOT to the list
(use your own address!) List problems? Notify [EMAIL PROTECTED]
--------------------------------------------------------------------
