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https://issues.apache.org/jira/browse/JENA-1841?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17052075#comment-17052075
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Andy Seaborne commented on JENA-1841:
-------------------------------------

First solution: It is guessing the URI from the class and also the lexical 
form. That works in the presented use case but is not a general solution: e.g. 
a custom datatype supposed to be in another ontology (e.g. QUDT).

Relying toString is unsafe.  Just because UUID happens to work, does not mean 
other other java classes will. May get "Object.toString".

We agree that automatic registration of an AdhocDatatype is incorrect.

I prefer an exception because a proper datatype can't be created - there is not 
enough information at the point in AbstractQueryBuilder (no URI available - the 
user didn't provide one).

You propose generating a URI and making the lexical form from toString.
It will not create the value again when parsing 0 - a setup-time registration 
that pairs the URI to the datatype implementation does.

Try your solution with the gist, removing the registration line. n1 is a 
string. The parse does not recover an UUID (it's a BaseDatatype placeholder 
TypedValue).

Background: SPARQL evaluation does not use java<->RDF mapping. Instead it 
implements XSD and F&O - needed to get the details right.

> Side Effect of Datatype <java:java.util.UUID> Use in Query
> ----------------------------------------------------------
>
>                 Key: JENA-1841
>                 URL: https://issues.apache.org/jira/browse/JENA-1841
>             Project: Apache Jena
>          Issue Type: Bug
>    Affects Versions: Jena 3.14.0
>            Reporter: Jan Martin Keil
>            Priority: Major
>
> I faced a bug caused by a side effect of using the datatype 
> <java:java.util.UUID> in a query.
> Short story is that you can not use this datatype in model parsing or queries 
> after you once used it in a query.
> I did not completely  break it down to a specific piece of code, but I wrote 
> some testcases that narrow down the issue. Please note that the order of 
> execution of the test methods effect the result. So please first try to 
> execute single test methods before executing the whole test class.
> {code:java}
> import java.io.ByteArrayInputStream;
> import java.util.UUID;
> import org.apache.jena.arq.querybuilder.SelectBuilder;
> import org.apache.jena.query.QueryExecution;
> import org.apache.jena.query.QueryExecutionFactory;
> import org.apache.jena.rdf.model.Model;
> import org.apache.jena.rdf.model.ModelFactory;
> import org.junit.jupiter.api.Test;
> public class UuidParsingintoModelOrQuery {
>       @Test
>       public void uuidParsingIntoSingleModel() throws Exception {
>               UUID uuid1 = 
> UUID.fromString("00000000-0000-0000-0000-000000000000");
>               UUID uuid2 = 
> UUID.fromString("00000000-0000-0000-0000-000000000001");
>               String modelStr = "_:a <http://example.org/p1> \"" + uuid1 + 
> "\"^^<java:java.util.UUID> .\n"
>                               + "_:a <http://example.org/p2> \"" + uuid1 + 
> "\"^^<java:java.util.UUID> .";
>               ModelFactory.createDefaultModel().read(new 
> ByteArrayInputStream(modelStr.getBytes()), "", "N-TRIPLE");
>               // repeat
>               modelStr = "_:a <http://example.org/p1> \"" + uuid2 + 
> "\"^^<java:java.util.UUID> .\n"
>                               + "_:a <http://example.org/p2> \"" + uuid2 + 
> "\"^^<java:java.util.UUID> .";
>               ModelFactory.createDefaultModel().read(new 
> ByteArrayInputStream(modelStr.getBytes()), "", "N-TRIPLE");
>       }
>       @Test
>       public void sameUuidParsingIntoSingleModel() throws Exception {
>               UUID uuid1 = 
> UUID.fromString("00000000-0000-0000-0000-000000000002");
>               UUID uuid2 = 
> UUID.fromString("00000000-0000-0000-0000-000000000003");
>               String modelStr = "_:a <http://example.org/p1> \"" + uuid1 + 
> "\"^^<java:java.util.UUID> .\n"
>                               + "_:a <http://example.org/p2> \"" + uuid2 + 
> "\"^^<java:java.util.UUID> .";
>               ModelFactory.createDefaultModel().read(new 
> ByteArrayInputStream(modelStr.getBytes()), "", "N-TRIPLE");
>               // repeat
>               ModelFactory.createDefaultModel().read(new 
> ByteArrayInputStream(modelStr.getBytes()), "", "N-TRIPLE");
>       }
>       @Test
>       public void sameUuidParsingIntoMultipleModel() throws Exception {
>               UUID uuid = 
> UUID.fromString("00000000-0000-0000-0000-000000000004");
>               String modelStr = "_:a <http://example.org/p1> \"" + uuid + 
> "\"^^<java:java.util.UUID> .";
>               ModelFactory.createDefaultModel().read(new 
> ByteArrayInputStream(modelStr.getBytes()), "", "N-TRIPLE");
>               ModelFactory.createDefaultModel().read(new 
> ByteArrayInputStream(modelStr.getBytes()), "", "N-TRIPLE");
>       }
>       @Test
>       public void uuidUseInQuery() throws Exception {
>               UUID uuid = 
> UUID.fromString("00000000-0000-0000-0000-000000000005");
>               SelectBuilder select = new SelectBuilder();
>               select.addWhere("?a", "<http://example.org/p>", "?uuid");
>               select.addFilter(select.getExprFactory().eq("?uuid", uuid));
>               QueryExecution q = QueryExecutionFactory.create(select.build());
>       }
>       @Test
>       public void uuidParsingIntoQuery() throws Exception {
>               UUID uuid = 
> UUID.fromString("00000000-0000-0000-0000-000000000006");
>               SelectBuilder select = new SelectBuilder();
>               select.addWhere("?a", "<http://example.org/p>", "?uuid");
>               select.addFilter(select.getExprFactory().eq("?uuid", uuid));
>               QueryExecution q = 
> QueryExecutionFactory.create(select.toString());
>       }
>       @Test
>       public void uuidUseInQueryAndParsingIntoModel() throws Exception {
>               UUID uuid = 
> UUID.fromString("00000000-0000-0000-0000-000000000007");
>               SelectBuilder select = new SelectBuilder();
>               select.addWhere("?a", "<http://example.org/p>", "?uuid");
>               select.addFilter(select.getExprFactory().eq("?uuid", uuid));
>               QueryExecution q = QueryExecutionFactory.create(select.build());
>               String modelStr = "_:a <http://example.org/p1> \"" + uuid + 
> "\"^^<java:java.util.UUID> .\n"
>                               + "_:a <http://example.org/p2> \"" + uuid + 
> "\"^^<java:java.util.UUID> .";
>               Model model = ModelFactory.createDefaultModel().read(new 
> ByteArrayInputStream(modelStr.getBytes()), "",
>                               "N-TRIPLE");
>       }
> }
> {code}



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