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 Tech@Spree Engineering GmbH
> mailto:mbo.tech@spree.de 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:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!
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