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http://issues.apache.org/jira/browse/JDO-246?page=comments#action_12364812 ]
Michael Bouschen commented on JDO-246:
--------------------------------------
I'm a little confused about the term intersection. Just for my understanding:
do you mean Cartesian product?
Here is my understanding of the semantics of your query including the resource
variable. Please note, this does not necessarily mean it needs to be
implemented that way :-):
The query first calculates the Cartesian product for Department, Employee and
Resource: Department x Employee x Resources. This results in a set of triples.
It then retains only those triples where the employee *and* the resource have a
relationship to the department in the first column of the triple. The Select
clause then defines values that are really returned by the query:
employee.name, employee.manager.lastname, resource.name. So the departments are
not included in the result.
Then the query result would be:
{"Employee1", "emp2Last", "Resource2"}
{"Employee3", null, "Resource2"}
{"Employee2", "emp2Last","Resource2"}
{"Employee2", "emp2Last","Resource3"}
{"Employee2", "emp2Last","Resource1"}
{"Employee1", "emp2Last","Resource1"}
{"Employee1", "emp2Last","Resource2"}
{"Employee2", "emp2Last","Resource1"}
{"Employee2", "emp2Last","Resource2"}
Rows 1 and 2 represent values for department dept1, rows 3-5 for dept2 and rows
6-9 for dept3.
About the difference between uisng && or ||:
I think with && only those tripels are retained where both the employee and the
resource have a relationship to the department of the triple. Using || the set
of retained tripels before the projection is bigger, because it also includes
tripels where only one of the two (employee, resource) is related to the
department.
Does this make sense?
> JPOX eliminates duplicates in the query result although DISTINCT is not
> specified.
> ----------------------------------------------------------------------------------
>
> Key: JDO-246
> URL: http://issues.apache.org/jira/browse/JDO-246
> Project: JDO
> Type: Bug
> Components: tck20
> Reporter: Michael Watzek
> Assignee: Erik Bengtson
>
> Test case NPEInResultExpr fails because the result of the query below is
> expected to contain duplicates. JPOX eliminates the duplicates.
> 14:22:55,046 (main) DEBUG [org.apache.jdo.tck] - Executing API query: SELECT
> employee.manager.lastname FROM org.apache.jdo.tck.pc.company.Department WHERE
> employees.contains(employee) VARIABLES Employee employee
> 14:22:55,078 (main) DEBUG [org.apache.jdo.tck] - Query result: [emp2Last,
> null]
> 14:22:55,078 (main) DEBUG [org.apache.jdo.tck] - Wrong query result:
> expected: [emp2Last, null, emp2Last, emp2Last, emp2Last]
> got: [emp2Last, null]
> 14:22:55,078 (main) INFO [org.apache.jdo.tck] - Exception during setUp or
> runtest:
> junit.framework.AssertionFailedError: Assertion A14.6.9-4 (NPEInResultExpr)
> failed:
> Wrong query result:
> expected: [emp2Last, null, emp2Last, emp2Last, emp2Last]
> got: [emp2Last, null]
> at junit.framework.Assert.fail(Assert.java:47)
> at org.apache.jdo.tck.JDO_Test.fail(JDO_Test.java:546)
> at org.apache.jdo.tck.query.QueryTest.queryFailed(QueryTest.java:500)
> at
> org.apache.jdo.tck.query.QueryTest.checkQueryResultWithoutOrder(QueryTest.java:485)
> at org.apache.jdo.tck.query.QueryTest.execute(QueryTest.java:1189)
> at org.apache.jdo.tck.query.QueryTest.execute(QueryTest.java:1029)
> at
> org.apache.jdo.tck.query.QueryTest.executeAPIQuery(QueryTest.java:966)
> at
> org.apache.jdo.tck.query.QueryTest.executeAPIQuery(QueryTest.java:946)
> at
> org.apache.jdo.tck.query.result.NPEInResultExpr.testPositive(NPEInResultExpr.java:106)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:324)
> at junit.framework.TestCase.runTest(TestCase.java:154)
> at org.apache.jdo.tck.JDO_Test.runBare(JDO_Test.java:204)
> at junit.framework.TestResult$1.protect(TestResult.java:106)
> at junit.framework.TestResult.runProtected(TestResult.java:124)
> at junit.framework.TestResult.run(TestResult.java:109)
> at junit.framework.TestCase.run(TestCase.java:118)
> at junit.framework.TestSuite.runTest(TestSuite.java:208)
> at junit.framework.TestSuite.run(TestSuite.java:203)
> at junit.framework.TestSuite.runTest(TestSuite.java:208)
> at junit.framework.TestSuite.run(TestSuite.java:203)
> at junit.textui.TestRunner.doRun(TestRunner.java:116)
> at junit.textui.TestRunner.doRun(TestRunner.java:109)
> at
> org.apache.jdo.tck.util.BatchTestRunner.start(BatchTestRunner.java:120)
> at org.apache.jdo.tck.util.BatchTestRunner.main(BatchTestRunner.java:95)
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