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https://issues.apache.org/jira/browse/JENA-1170?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15260435#comment-15260435
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ASF subversion and git services commented on JENA-1170:
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Commit 8d4cb56005332638a24e13fda571680a8ed23fa0 in jena's branch
refs/heads/master from [~andy.seaborne]
[ https://git-wip-us.apache.org/repos/asf?p=jena.git;h=8d4cb56 ]
JENA-1170 : Map<Var, ? extends Var> and allow var -> var substitution.
> QueryTransformLib cannot rename varibales
> -----------------------------------------
>
> Key: JENA-1170
> URL: https://issues.apache.org/jira/browse/JENA-1170
> Project: Apache Jena
> Issue Type: Improvement
> Components: ARQ
> Affects Versions: Jena 3.0.1
> Reporter: Claus Stadler
>
> Renaming variables of a query - a rather basic use case when transforming
> queries - does not work with the snippet below due to a raised exception:
> {code:java}
> Map<Var, Node> vmap = Collections.singletonMap(Var.alloc("a"),
> (Node)Var.alloc("x"));
> Query foo = QueryFactory.create("Select ?a { ?a ?b ?c }");
> Query bar = QueryTransformOps.transform(foo, vmap);
> {code}
> The reason is, that the way QueryTransformOps.transformVarExprList[1] is
> implemented, prevents this. Also, a much nicer (unfortunately private)
> implementation already exists at Transformer.ApplyTransformVisitor.process[2]
> I suggest to make [2] publicly accessible (e.g. as part of one of the
> TransformLibs or a VarExprUtils) and implement [1] based on that:
> {code:java}
> class QueryTransformOps {
> private static void transformVarExprList(VarExprList varExprList,
> ExprTransform exprTransform)
> {
> VarExprList tmp = VarExprListUtils.transform(varExprList,
> exprTransform);
> VarExprListUtils.replace(varExprList, tmp);
> }
> }
> class VarExprListUtils {
> public static void replace(VarExprList dst, VarExprList src) {
> if(dst != src) {
> dst.clear();
> copy(dst, src);
> }
> }
> public static void copy(VarExprList dst, VarExprList src) {
> for(Var v : src.getVars()) {
> Expr e = src.getExpr(v);
> if(e == null) {
> src.add(v);
> } else {
> src.add(v, e);
> }
> }
> }
> }
> {code}
> [1]
> https://github.com/apache/jena/blob/master/jena-arq/src/main/java/org/apache/jena/sparql/syntax/syntaxtransform/QueryTransformOps.java#L74
> [2]
> https://github.com/apache/jena/blob/master/jena-arq/src/main/java/org/apache/jena/sparql/algebra/Transformer.java#L243
> As a side note, it would be convenient, if the transform method also accepted
> a Map<Var, Var> - i.e. changing the method signature to accept a Map<Var, ?
> extends Node>
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