Re: JDOQL query problems (JPOX issues?)

Sat, 28 Oct 2006 09:50:48 -0700 

Hi Erik,

I fully agree with Craig's description of what the queries should return.

Michael,

I was reading Craig comments and noted that "str" is an unbound variable and not
a parameter, and now I think the query is invalid since there is no value for
str.
Yes, str is a varaible and not a parameter. But why is it unbound? There is a contains clause binding the variable to field stringCol which is a collection of strings: 
 q.setFilter("this.stringCol.contains(str)");
The third query binds the variable b to the collection of B instances called bCol: 
 q.setFilter("this.bCol.contains(b)");

Here are the three queries in single string JDOQL:
SELECT str FROM A WHERE this.stringCol.contains(str) VARIABLES String str GROUP BY str SELECT str, count(this) FROM A WHERE this.stringCol.contains(str) VARIABLES String str GROUP BY str SELECT b count(this) FROM A WHERE this.bCol.contains(b) VARIABLES B b GROUP BY b
Here is the SQL query for the second JDOQL query. Suppose class A is mapped to table TABLE_A and the string collection to table STRING_TABLE. This table has a foreign key to table A and a VARCHAR column called text. SELECT s.text, COUNT(a.id) FROM TABLE_A a, STRING_TABLE s WHERE s.a_id = a.id GROUP BY s.text I'm currently using this SQL query as a workaround and create a Query instance with the "javax.jdo.query.SQL" language parameter. It returns the expected result! 

Regards Michael

Unbound variables are not null values.

Quoting Craig L Russell <[EMAIL PROTECTED]>:


Hi Michael,

 From the spec,
<spec>
The candidate tuples
are the cartesian product of the candidate class and all variables
used in the result. The re-
sult tuples are the tuples of the candidate class and all variables
used in the result that sat-
isfy the filter. The result is the collection of result expressions
projected from the result
tuples.
</spec>

On Oct 27, 2006, at 2:12 PM, Michael Bouschen wrote:


Hi,

I'm having problems running JDOQL queries that group by a variable.
I think the queries below are valid, but I would like to double
check this. If you agree that the queries are valid JDOQL, I will
check the TCK to add these queries to existing TCK tests or add new
test cases. I tried the queries with JPOX version 1.1.3 and with
the nightly build from Oct 27 (no difference). I will send a test
case to reproduce the problem to Erik and Andy, since I cannot
attach archives here.

The class model is simple: pc class A has a field stringCol which
is a collection of strings and another field bCol which is a
collection of instances of class B.

The following query groups the class A instances by the strings in
their string collection:
 Query q = pm.newQuery(A.class);
 q.declareVariables("java.lang.String str");
 q.setFilter("this.stringCol.contains(str)");
 q.setGrouping("str");
 q.setResult("str");

The cartesian product of the candidate class and all variables is a
the cartesian product of all A instances and all strings contained in
any stringCol. The result tuples consist of tuples of (A, String)
where the elements of stringCol are projected and associated with the
instances of A whence they came. The result comes from grouping and
projecting the String from the result tuple. So,

This query should collect all of the unique strings in all instances
of A stringCol. The result is a List<String>. I don't know offhand
how the implementation can do this trick (returning a List<Object> in
which each element is a String is easy).


This results in an exception:
 JDOUserException: Unable to find the field "str" in the candidate
class. It is possible that this field is a field in a subclass, but
it is illegal to reference fields directly when they are in a
subclass.

I get a different exception when adding an aggregate to the result
clause
 q.setResult("str, count(this)");
 JDOUserException: Unconstrained variable referenced: str

This query should collect all of the unique strings in all instances
of A stringCol, count them, and return the string and count of
occurrences. The result is a List<Object[ ]> Each element consists of
an Object[ ] containing a String in element 0 and a Long in element 1.

The behavior is different when iterating a collection of pc instances:
  Query q = pm.newQuery(A.class);
  q.declareVariables("model.B b");
  q.setFilter("this.bCol.contains(b)");
  q.setGrouping("b");
  q.setResult("count(this), b");
This results in:
 JDOUserException: The result clause has a field expression
"UnboundVariable "UNBOUND_B.ID"" that doesnt appear in the
grouping. Any result specification has to be present in the
grouping when grouping is specified.

This query should collect all of the unique B instances in all
instances of A bCol, count them, and return the B and count of
occurrences. The result is a List<Object[ ]> Each element consists of
an Object[ ] containing a B in element 0 and a Long in element 1.

Craig

Any help is appreciated. Thanks!

Regards Michael

--
Michael Bouschen                [EMAIL PROTECTED] Engineering GmbH
mailto:[EMAIL PROTECTED]        http://www.tech.spree.de/
Tel.:++49/30/235 520-33         Buelowstr. 66
Fax.:++49/30/2175 2012          D-10783 Berlin


Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!








--
Michael Bouschen                [EMAIL PROTECTED] Engineering GmbH
mailto:[EMAIL PROTECTED]        http://www.tech.spree.de/
Tel.:++49/30/235 520-33         Buelowstr. 66                   
Fax.:++49/30/2175 2012          D-10783 Berlin

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